Prepared for:

U.S. Forest Service

Mount Hood National Forest

FINAL REPORT

Oregon Route 224 Corridor Study:

Phase 1 – Existing Conditions Assessment

Prepared by:

Federal Highway Administration

Western Federal Lands Highway Division

October 2021
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Table of Contents

Executive Summary................................................................................................................. 1

Introduction.............................................................................................................................. 2

Background.......................................................................................................................................2

Corridor Study Area..........................................................................................................................2

Existing Conditions Reports and Recovery Efforts.......................................................................4

Riverside Fire BAER Report .........................................................................................................4

Fire Recovery Work Completed Since September 2020 ..............................................................4

Baseline Conditions Summary: OR 224 Corridor Context................................................... 5

Safety and Traffic Assessment........................................................................................................5

Traffic Data....................................................................................................................................5

Road Users and Corridor Uses .....................................................................................................6

Existing Guardrail and Roadside Condition ..................................................................................7

Interactive Highway Safety Design Model (IHDSM) Description...................................................8

Traffic and Safety Assessment Recommendations ....................................................................11

Unstable Slope Gap Analysis and On-Site Ratings Assessment...............................................18

Corridor Geology.........................................................................................................................18

Site Conditions............................................................................................................................20

Analysis Method..........................................................................................................................20

Analysis Results..........................................................................................................................21

Unstable Slope Assessment Recommendations ........................................................................22

Hydrology Gap Analysis ................................................................................................................23

Available Data and Suitability......................................................................................................23

Corridor Needs and Data Gaps...................................................................................................25

Hydrology Assessment Recommendations ................................................................................27

Future Study Efforts ....................................................................................................................27

Summary of Technical Recommendations and Areas of Further Study ...................................28

Phase 2 - OR 224 Corridor Master Plan Scoping ................................................................ 30

Proposed Work Summary ..............................................................................................................30

High-Level Phase 2 Master Plan Scope ........................................................................................30

Option for Planning and Environmental Linkages (PEL) ............................................................32

Phase 2 Corridor Master Plan Cost Estimate...............................................................................32

Appendix A - Safety and Traffic Assessment Technical Memorandum........................33

Appendix B - Unstable Slope Gap Analysis and On-Site Ratings Assessment Technical 

 Memorandum....................................................................................88

Appendix C - Hydrology Gap Analysis Technical Memorandum................................113
1

Executive Summary

In 2020, the Mount Hood National Forest experienced unprecedented catastrophic wildfire events that 

damaged recreational sites and transportation assets along the Clackamas River corridor. A 19-mile 

segment of OR 224, the primary route connecting travelers from the Portland metro area to the forest, 

has been closed to the public since the Riverside Fire due to hazardous conditions and ongoing 

rehabilitation work. Post-fire assessments and emergency repairs have been completed over the past 

year to determine the scale of damage, anticipate high-risk areas in the changed landscape, and 

stabilize the roadway.

To leverage the ongoing recovery efforts happening in the Mount Hood National Forest, the U.S. Forest 

Service (USFS) requested technical planning assistance from the Federal Highway Administration 

(FHWA) Office of Federal Lands Highway Western Federal Lands Highway Division (WFLHD) to 

complete an Existing Conditions Assessment of the OR 224 corridor to better understand the extent of 

post-wildfire conditions as they relate to future use and transportation system resiliency within the 

National Forest. The Phase 1 Existing Conditions Assessment is the first of a two-phase Corridor Study 

for OR 224 and its purpose is to evaluate and document current baseline conditions along the closed 

portion of the corridor with a focus on safety, traffic operations, unstable slopes, and hydrology 

features. 

The findings from the Phase 1 Existing Conditions Assessment include technical recommendations, 

data gaps, and areas of further study for a Phase 2 OR 224 Corridor Master Plan. A high-level Phase 2 

Corridor Master Plan scope and project budget was also developed to assist the USFS and ODOT in 

seeking additional funding resources for comprehensive planning, as they become available. While this 

Phase 1 baseline assessment offers valuable insights into current conditions, a Corridor Master Plan is 

needed to develop a long-term, coordinated vision and related goals for the impacted area, further 

investigate high risk areas along the corridor, develop initial site designs for priority transportation 

improvements, and identify a comprehensive suite of capital projects and policy recommendations that 

support the many uses of the Mount Hood National Forest while enhancing transportation access.
2

Introduction

Background

In 2020, the Mount Hood National Forest experienced unprecedented catastrophic wildfire events that 

damaged recreational sites, roadways, office and storage buildings, and other critical infrastructure 

along the Clackamas River corridor. A 19-mile segment of OR 224, the primary route connecting 

travelers from the Portland metro area to the forest, has been closed to the public since the Riverside 

Fire due to hazardous conditions and ongoing rehabilitation work. The U.S. Forest Service (USFS) has 

requested assistance from the Federal Highway Administration (FHWA) Office of Federal Lands 

Highway Western Federal Lands Division (WFL) to complete an Existing Conditions Assessment of the 

OR 224 corridor to better understand the extent of post-wildfire conditions as they relate to future use 

and transportation system resiliency within the National Forest.

This report is the first of a two phase Corridor Study for the wildfire-impacted OR 224 in the Mount 

Hood National Forest. The purpose of the Phase 1 – Existing Conditions Assessment is to evaluate and 

document current baseline conditions along the closed portion of OR 224, with a focus on safety, traffic 

operations, unstable slopes, and hydrology features. Information gathered during the post-wildfire 

baselining effort will be used to inform future study efforts that identify project-specific transportation

improvements. WFL will document these additional areas of in-depth analysis to be completed in a 

Phase 2 – Corridor Master Plan as part of this Phase 1 effort. 

Corridor Study Area

This corridor study is focused on the closed section of OR 224, located between Promontory Park and 

Ripplebrook (Mile Post (MP) 31.2 through MP 49.97). Figure 1 depicts the study area location within the 

Mount Hood National Forest. 

Figure 1: OR 224 Phase 1 Study Area Corridor
3

The area surrounding OR 224 is characterized by a multitude of uses, including timber management, 

hydroelectric power transmission, regional drinking water treatment, technical career training, and 

outdoor recreation. The Clackamas River and OR 224 roadway, which runs parallel to the river, have 

both received national recognition for providing an exceptional visitor experience. These recognitions 

include:

• West Cascades Oregon National Scenic Byway

• Clackamas National Wild and Scenic River and State Scenic Waterway 

• Cascading Rivers Scenic Bikeway

Many of the exceptional qualities that characterized the corridor were impacted by the 2020 wildfires

and have altered visitation to the forest and surrounding gateway communities. While the Riverside Fire 

began in the Mount Hood National Forest, it spread northwest along the Clackamas Basin towards the 

city of Estacada and burned within a half mile of the downtown. Various river-dependent outfitters and 

boating groups are based in Estacada and were not able to access popular launch areas along the 

Clackamas River due to dangerous conditions. The closures that are currently in place have limited 

recreational travel to Estacada, resulting in significant impacts to the local economy.

In addition to recreation uses, the OR 224 corridor provides access to utility providers serving the 

Portland metro area. Portland General Electric (PGE) owns and operates the Clackamas River 

Hydroelectric Project, which is a series of four powerhouses, dams, reservoirs, and related facilities, 

including managed recreational sites. Nearly all of the Clackamas River Hydroelectric Project is located 

within the Mount Hood National Forest and the complex generates approximately 139 megawatts of 

power. While the Riverside Fire did not directly damage any of the hydroelectric generating facilities, 

other recreation sites and connecting transportation systems were closed due to fire impacts. 

While personal property damage was minimal in the aftermath of the 2020 Riverside fire, other dangers 

arise in the aftermath. Many nearby communities rely on the Mount Hood National Forest for municipal 

water supplies. The Clackamas River is managed by various entities with agreements with the USFS, 

including the North Clackamas Water Commission and South Fork Water Board. Various water 

systems experienced interruption of service and access to water treatment plants, resulting in boil water 

notices. 

The Riverside Fire burned through timber stands in the Mount Hood National Forest that were covered 

by federal logging contracts. In the Clackamas River Ranger District, two timber sale advertisements 

were cancelled because the hauling routes either needed to be mitigated or reassessed due to fire 

damages. While it is unclear how much post-fire logging will occur as the forest recovers, this issue 

highlights the importance of the regional transportation network in timber production.
4

Existing Conditions Reports and Recovery Efforts

Riverside Fire BAER Report

In October 2020, a Burned Area Emergency 

Response (BAER) team, including scientists, 

engineers, and recreation specialists, surveyed 

the Riverside Fire impacted area. The BAER team 

identified imminent post-wildfire threats to human 

life and safety, property, and critical natural or 

cultural resources and made emergency 

stabilization recommendations.

Fire Recovery Work Completed Since 

September 2020

Over the past year, the USFS and ODOT have 

been assessing damage and repair costs for 

impacted infrastructure, performing environmental 

analysis, remedying unsafe conditions and 

hazmat, and implementing emergency repair 

projects. Many Clackamas River Ranger District 

employees’ work has been redirected to support 

fire recovery. 

According to the Mount Hood National Forest 

Clackamas River Ranger District, the following 

recovery work has been completed:

• Assessment of fire damage to soil, water 

resources, wildlife, and estimated tree mortality

• Environmental analysis required for danger tree abatement project on forest roads

• Containment of hazmat materials 

• Removal & clean-up of burned vault toilets

• Debris slide catchment

• Hazard tree removal around Ripplebrook

• Installation of road and recreation site warning signs

• Installation and maintenance of closure gates for public safety

• New Remote Automated Weather Station (RAWS) to monitor storms, fire, slides, & emergency 

weather

• Ordered seedlings from Forest Service nursery for reforestation. Seeds were collected in the 

past from Mount Hood and areas with similar genetic makeup.

• Felled and cleared danger trees along FR 4220 and around Olallie Lake Resort to allow safe 

reopening of Olallie Lake in July.

• Noxious week surveys and treatment (~80 acres)

• Worked with PGE to clear hazards to power transmission lines

• Using local contractor, converted fire debris slash piles into biochar for future restoration 

projects 

• Cleared Memaloose Rd to allow installation of communications equipment for local emergency 

services

• Cleared 18 miles of trails of downed trees and limbs

Figure 2: Comparison of pre- and post-fire imagery in the 

Clackamas River Ranger District (Source: USFS Riverside Fire 

Story Map)
5

Baseline Conditions Summary: OR 224 Corridor Context

A critical first step in developing a comprehensive corridor study is to gather, organize, and analyze 

available sources of data about the current transportation system. The wildfire-impacted OR 224 

corridor must be inventoried before decisions can be made on how to address specific problems within 

the constraints of future funding availability. This baselining effort allows the USFS and ODOT to 

understand the many needs that must be addressed in order to improve safety and access for all users. 

The following sections present initial findings and data gaps related to safety, traffic operations, 

unstable slopes, and hydrology. This transportation-specific assessment is complementary to and 

supports the findings of the Riverside BAER report.

Safety and Traffic Assessment

An analysis of safety and operational concerns was conducted by the WFLHD Highway Safety Team

as part of the Phase 1 Corridor Study effort, focused mostly on baseline pre-wildfire conditions with 

additional consideration given to future forest uses and users. Recommendations, where possible, are 

based on available information, but may require additional resources or further study. Items reviewed 

and/or used for analysis as part of the safety and traffic assessment included:

• The ODOT TransGIS portal, which provides information on traffic data, lane widths, shoulder 

widths, mileposts (MP), signs, roadside barrier, and posted speed limits

• The ODOT Crash Data System, which provides location-specific crash history

• The ODOT guardrail damage inventory

• The Interactive Highway Safety Design Model (IHSDM), which is described below

• Aerial Imagery through a Bing Maps GIS layer

• Quadrangle maps through the United States Geologic Service (USGS)

• The Clackamas County Flood Insurance Study (FIS), which helped confirm the general grade of 

the river and the road (which generally follows the river throughout the corridor); the quad maps 

were the primary source of topographic data

• OpenRoads Designer, from which an approximated alignment was created to provide data for 

use by IHSDM

• The plan set for the OR DOT 224(1) Clackamas Highway Pavement Restoration Project (MP 

31.73-MP 33.00 and MP 44.94-45.82)

• The ODOT Digital Video Log

This safety and traffic assessment has been mostly focused on baseline, pre-disaster conditions with 

some additional consideration given to future forest uses, users, and other considerations. 

Recommendations, where possible, are based on available information, but may sometimes require 

additional information or further study. A comprehensive assessment is included as Appendix A –

Safety and Traffic Assessment Final Memorandum.

Traffic Data

The following average annual daily traffic (AADT) volumes, for both the current year and a potential 

design year (current year + 20 years) were retrieved from the ODOT TransGIS portal:

• MP 31.2-MP 39.1

o Current year: 560 vehicles per day

o Design year: 760 vehicles per day

• MP 39.1-MP 42.2

o Current year: 550 vehicles per day

o Design year: 760 vehicles per day

• MP 42.2-MP 48.3
6

o Current year: 480 vehicles per day

o Design year: 480 vehicles per day

• MP 48.3-MP 49.97

o Current year: 300 vehicles per day

o Design year: 320 vehicles per day

The percentage of the AADT that is truck traffic is 36.9% for all above segments, according to 

TransGIS. There is significant potential for seasonal traffic volumes to be significantly higher than the 

AADT volumes listed above. A potential goal for a future study would be to confirm traffic volumes 

within the corridor (including at some of the more prominent intersections and driveways). This 

confirmation may help planning or design efforts if there are ever future projects to add or upgrade 

parking, campground, or other forest features that would draw visitation and, potentially, congestion or 

user conflicts along with it. Posted speed limits are 55 MPH.

Road Users and Corridor Uses

OR 224 is an important link of the West Cascades Scenic Byway and the Cascading Rivers Scenic 

Bikeway. There are currently no counts available for bicycle traffic, but the USFS did note at the June 

2021 site visit that on a drive-through it is possible to see six to ten cyclists using the road. Bicycle 

traffic may also grow in the future if the corridor’s reputation as an enjoyable place to ride continues to 

grow. It is possible to gather bicycle counts once the corridor is reopened to the public; however, 

without previous baseline or pre-disaster bicycle counts, it will be more difficult to project bicycle traffic 

growth.

Pedestrians are an additional road user group to consider as part of future corridor uses. Currently, 

there are no marked or signed pedestrian crossings within the study limits. However, the USFS noted 

that it is common for pedestrians to cross the road to access areas on the opposite side from where 

they park. Campgrounds, boating access areas, and other defined recreational features are the areas 

where these pedestrian crossings are most likely to occur, but with vehicles parking at a large number 

of places throughout the corridor, the potential for pedestrian crossings is increased. Additionally, there 

is concern that with the loss of vegetation that may have previously served as a barrier to access, 

pedestrian crossings may become even more hazardous in the future as access points have increased 

and are even less defined or obvious to drivers.

The USFS identified some of the primary ways in which those who access this area of Mount Hood 

National Forest use this corridor:

• Scenic driving, including motorcycle or bicycle traffic

• Camping, including on and off designated campgrounds

• Hiking, picnicking, mushroom picking, target shooting, and other ‘on foot’ activities

• River activities, including boating and kayaking

• Winter sports and activities, including snowshoeing and cross country skiing

• Commercial activities, including maintenance of the hydroelectric facilities, other utilities, or 

logging activities (including through traffic)

The above list is not all-inclusive, and the complete list of needs for each of those uses is outside of the 

scope of a safety and traffic assessment. However, these needs must be considered when intersecting 

with corridor safety needs, parking needs, and other traffic needs. Currently, there are a large number 

of vehicles parking at undesirable locations throughout the entire corridor, creating safety and 

environmental concerns. Parking in undesirable areas is expected to be exacerbated following the loss 

of vegetation. Visitors who park in these undesirable areas may also be participating in other activities, 

such as target shooting or camping, in undesirable or unsafe areas. Another consideration is the 

different goals of the road users. Some of those visiting the corridor for scenic driving or other 
7

recreational activities may at times be driving at lower speeds. Those using the corridor for commercial 

activities may be incentivized to travel at higher speeds. These speed differentials, while difficult to 

model when caused by recreation, can increase the risk of crashes.

Existing Guardrail and Roadside Condition

Extensive guardrail damage was observed throughout the corridor. An accounting of the following will 

be needed:

1. Guardrail damaged by during the disaster or during disaster-recovery that will be replaced inkind once the post-disaster logging activities are complete.

2. Guardrail (specifically guardrail that does not meet current crash testing criteria) that was not 

damaged and will not be replaced in kind.

3. Locations where there is no existing guardrail but, with post-disaster conditions, may be 

warranted as part of a potential future project.

An inventory of all existing guardrail in the corridor (from ODOT TransGIS, see above link) is included

in Appendix A. Given the high risk of slides or fallen trees throughout the corridor, it is assumed that 

continued monitoring of the roadside is needed as more guardrail may become damaged until the area 

stabilizes. The area may not fully restabilize until the downslopes become revegetated.

The starting point for evaluating where new guardrail may be needed is an evaluation of the clear zone 

throughout the corridor. According to Section 3.1 of the AASHTO Roadside Design Guide, the clear 

zone is the unobstructed, traversable area provided beyond the edge of the traveled way for the 

recovery of errant vehicles. The shoulder, any turnouts, and any roadside area free of obstructions with 

a slope ratio that is 1 vertical to 4 horizontal (1V:4H) or flatter are considered to be part of the clear 

zone. 

• Slopes 1V:4H are considered to be traversable and recoverable, meaning that an errant vehicle 

that reaches this type of slope can generally stop their vehicle or slow them enough to return to 

the roadway (if the slope is wide enough and free of obstructions).

• Slopes steeper than 1V:4H but flatter than 1V:3H are considered to be traversable but nonrecoverable. Errant vehicles that encounter slopes in this range cannot likely navigate back to 

the roadway or come to a complete stop, but can likely be expected to reach the bottom of the 

slope without rolling over. Slopes in this range are if there are no obstructions on the slope or at 

the toe of the slope, and if there are slopes 1V:4H or flatter at the toe, then the clear zone 

resumes at the toe of the slope where vehicles have the opportunity to safely come to a stop.

• Slopes steeper than 1V:3H are considered to be non-traversable and non-recoverable, meaning 

that vehicles that encounter slopes in this range cannot recover to the roadway and cannot 

safely steer to the bottom. Slopes in this range present a rollover risk that increases 

proportionately to slope steepness (especially for slopes steeper than 1V:2H). No field 

measurements were taken on the June 16, 2021 site visit, but based on observations and the 

contour lines from the USGS quad maps, it seems that most slopes in the corridor fall into this 

range. With the loss of vegetation, many roadside slopes appeared to be undergoing soil 

erosion, causing the slopes to steepen in areas where the soil has migrated down-slope.

The AASHTO Guidelines for the Geometric Design for Low Volume Roads may apply to this corridor 

when determining the recommended clear zone width since the average daily traffic is less than 2000 

vehicles per day, according to the ODOT Trans GIS site. However, until there is confirmation of 

seasonal highs in traffic volumes, it may be more appropriate to refer to Table 3-1 of the AASHTO 

Roadside Design Guide for recommended clear zone widths:

• Foreslopes (downhill):

o 1V:6H or flatter – 12 to 14 feet
8

o 1V:5H to 1V:4H – 14 to 18 feet

• Backslopes (uphill):

o 1V:3H – 8 to 10 feet

o 1V:5H to 1V:4H – 10 to 12 feet

o 1V:6H or flatter – 10 to 12 feet

Interactive Highway Safety Design Model (IHDSM) Description

The IHDSM is a suite of software analysis tools for evaluating safety and operational effects of 

geometric design in the highway project development process. The IHSDM contains six modules that 

can be used to evaluate nominal and substantive safety performance. For this study, the Crash 

Prediction, Policy Review, Design Consistency, and Traffic Analysis Modules were used to evaluate the 

OR 224 corridor. 

With no available survey, a variety of sources were used to acquire or approximate the data needed to 

run IHSDM. A horizontal alignment was approximated in OpenRoads Designer with the use of aerial 

imagery. A vertical alignment was approximated with the use of USGS quad maps, and a drive-through 

of the corridor on the June 2021 site visit confirmed no significant grades or grade changes that would 

have a major effect on IHSDM output. Data for lane widths, shoulder widths, and guardrail locations 

were taken from the ODOT TransGIS site. Cross slope data was approximated to be 2% for a typical 

tangent section. For curve sections, the cross slopes were approximated to the appropriate 

superelevation for each radius as listed in the AASHTO Policy on Geometric Design of Highways and 

Streets (8% maximum table, Table 3-10). Inputs for the roadside data were based on the USGS quad 

maps, Google Streetview imagery, and aerial imagery. Traffic and crash data were as listed previously 

in this memorandum.

Key assumptions and additional context on the use of IHSDM and these four modules for this analysis 

are further described in Appendix A – Safety and Traffic Assessment Final Memorandum.

IHSDM Output Data Analysis

The IHDSM software divides the roadway into segments based on changes in roadway geometry, such 

as lane width, shoulder width, cross slope, or roadside hazard rating, as well as changes in traffic data 

or behavior. 206 segments were identified within this corridor. To ease the analysis of the output data, 

the segments were combined into 12 distinct groups based on similar features such as tangent 

sections, reverse curves, or similar roadside conditions. A description of the 12 groups is included in 

Table 1 below (see Appendix A for more information).

Table 1: IHDSM Roadway Segment Groups

Group 

Number

Start 

MP*

End 

MP* Description

1 31.2 32.6 Long, high radius curves; adjacent to significant recreational facility

2 32.6 34.5 Series of lower radius, shorter curves

3 34.5 35.6 Fairly straight section

4 35.6 37.8 Series of curves, including a change in horizontal alignment of approx. 180°

5 37.8 39.2 Fairly straight section

6 39.2 41.0 Series of curves, mix of medium and high radius

7 41.0 42.3 Fairly straight section

8 42.3 44.2 Series of curves, higher radius as compared to Group 8
9

9 44.2 46.4 Series of curves, including changes in horizontal alignment of approx. 90°

10 46.4 47.5 Fairly straight section

11 47.5 49.0 Winding section with curves of varying lengths, some lower radius

12 49.0 49.97 End of corridor, more driveways, lower speed limit

*Mileposts listed are approximate

The Design Consistency and Traffic Analysis Modules were used to help examine expected speeds 

throughout the corridor. IHSDM runs a speed model through the geometry, taking into account 

horizontal curves and vertical grades in order to determine the effects that geometry has on speed (e.g. 

faster on steeper downgrades, slower on steeper upgrades). The results are sensitive to the Desired 

Speed input, which is estimated here in absence of formal speed data. For a design speed such as 55 

mph, proposed for use on this project, an estimate of 65 mph was used since the corridor is 

characterized by long tangent sections with minimal significant grade changes. Anecdotally, as noted 

by the USFS at the June 2021 site visit, risky driving (and, at times, impaired driving) is commonplace 

enough during the high visitation season to be a significant concern. The speed model helps the project 

team with locating higher discrepancies between expected speed and design speed of individual 

geometric elements such as horizontal and vertical curves. This can help fine-tune countermeasures 

such as warning signage to better align with motorist’s expectations. 

Data gained through the Crash Prediction Module, the Policy Review Module, and the Design 

Consistency Module were used to compare groups (due to approximated data, the Driver/Vehicle 

Module failed to run and data from the Driver/Vehicle Module was not included in the results analysis). 

The comparison was completed with the following data:

1. Expected Crashes data adjusted by group length (crashes/group/mile). This data relies on an 

Empirical-Bayes analysis using historical crash data. This data is noted as ‘Expected Crashes’ 

for the remainder of the report.

2. Predicted Crashes data adjusted by group length (crashes/group/mile). This is the default model 

for crash prediction within IHSDM and relies on roadway geometry, roadside features and other 

program inputs. This data is noted as ‘Predicted Crashes’ for the remainder of the report. The 

predicted crash data is especially important for this analysis due to the age of the historical 

crash data.

3. Total expected crashes per group.

4. Total predicted crashes per group.

5. Design Consistency Module flagged data within each group (i.e. segment with an element not 

designed according to the AASTHO Green Book counted as one flag).

6. Policy Review Module flagged data within each group (i.e. each severe speed differential or 

deficient stopping sight distance within each segment counted as one flag).

These six items for each group were compared to their position with respect to the 90th percentile 

number and the 75th percentile number for each data set. For example, a group with predicted crashes 

based on Empirical-Bayes data in the 90th percentile as compared to all other groups received 1 point. 

A group with predicted crashes based on Empirical-Bayes data between the 75th percentile and the 

90th percentile as compared to all other groups received 0.5 points. Groups with Empirical-Bayes 

crashes data below the 75th percentile received 0 points. Scores were totaled for the 12 groups and 

then ranked. Several groups were identified for further analysis. The IHSDM analysis and results allows 

for data-driven safety analysis to identify the sections of the project that would benefit the most from 

specific safety features, discussed in the Existing Data Analysis section.

Existing Data Analysis
10

The 12 groups are identified and described within Appendix A. These groups were scored based on 

criteria numbers 1-6 identified in the above IHSDM Output Data Analysis section. The ranked by risk 

groups are shown in Table 2 below (see Appendix A for more information on the data and scoring):

Table 2: OR 224 Groups Ranked by Risk

Rank Group Start MP End MP

1 4 35.6 37.8

2 11 47.5 49.0

3 2 32.6 34.5

4 9 44.2 46.4

5 8 42.3 44.2

6 10 46.4 47.5

7 1 31.2 32.6

8 3 34.5 35.6

8 5 37.8 39.2

8 6 39.2 41.0

8 7 41.0 42.3

The Crash Prediction Module results for the corridor are in part summarized in Table 3 and Table 4:

Table 3: Comparing Crash Prediction Module Expected and Predicted (Existing Conditions - 20-Year Design Life)

Crash Prediction 

Module Method

Total 

Crashes

Fatal & Injury 

Crashes

Percent 

Fatal & 

Injury

Property Damage 

Only Crashes

Percent 

Property 

Damage Only

Predicted 108.24 34.74 32.10% 73.50 67.90%

Expected 137.12 70.84 51.67% 66.27 48.33%

% Difference 21.06% 50.95% 10.90%

Table 3 shows the breakdown of expected crashes by those resulting in Fatal and Injury (FI) and those 

resulting in Property Damage Only (PDO). As shown, between 32% and 52% of all crashes result in a 

fatality or an injury, indicating the risk of roadway departures in this corridor. A roadway departure crash 

occurs when there is a crash that involves a vehicle crossing centerline, an edge line, or a lane line.

The expected crash data, which relies on historical crash data, shows an elevated percentage of fatal 

and injury crashes. This is a strong indication that the risk of severe crashes in the corridor is higher 

than what could be anticipated when reviewing the roadway and roadside strictly by its geometry and 

features. Driver behavior may be one explanation. Expected and predicted crash data cover a 20-year 

design life and account for the projected increase in traffic volume (exposure) over time.
11

Table 4: Expected Crash Type Distribution (Existing Conditions – 20-Year Design Life)

Crash Type

Fatal and Injury Property Damage 

Only Total

Crashes Crashes 

(%) Crashes Crashes (%) Crashes Crashes (%)

Collision with Animal 2.69 2.00% 12.19 8.90% 16.59 12.10%

Collision with Bicycle 0.28 0.20% 0.07 0.00% 0.27 0.20%

Other Single-vehicle Collision 0.5 0.40% 1.92 1.40% 2.88 2.10%

Overturned 2.62 1.90% 0.99 0.70% 3.43 2.50%

Collision with Pedestrian 0.5 0.40% 0.07 0.00% 0.41 0.30%

Run Off Road 38.61 28.20% 33.47 24.40% 71.44 52.10%

Total Single Vehicle Crashes 45.20 33.00% 48.71 35.50% 95.02 69.30%

Right-Angle Collision 7.16 5.20% 4.77 3.50% 11.65 8.50%

Head-on Collision 2.41 1.80% 0.2 0.10% 2.19 1.60%

Other Multi-vehicle Collision 1.84 1.30% 1.99 1.40% 3.70 2.70%

Rear-end Collision 11.69 8.50% 8.09 5.90% 19.47 14.20%

Sideswipe 2.69 2.00% 2.52 1.80% 5.07 3.70%

Total Multiple Vehicle Crashes 25.79 18.80% 17.56 12.80% 42.09 30.70%

Total Expected Crashes 70.98 51.80% 66.27 48.30% 137.12 100.00%

Table 4 shows the expected crash type distribution. Single-vehicle crashes are highlighted in green. 

Multi-vehicle crashes are highlighted in yellow. Corridor totals are highlighted in orange. As shown, the 

largest number of crashes were single vehicle roadway departures. These three tables, in addition to all 

other IHDSM output especially those specific to the more at-risk groups, help to identify effective and 

cost-efficient crash reduction features that can be applied to the OR 224 corridor. 

Traffic and Safety Assessment Recommendations

Bicycle Facilities

Widening the roadway to accommodate 4- to 5-foot shoulders throughout the entire corridor would 

require a significant amount of earthwork, disturbance to environmentally-sensitive areas, potential 

bridge widening, and cost. While widening may be the ideal solution to accommodate cyclists, the 

below discussion is based on the roadway template remaining the same in the future.

There is readily available online marketing and information for the West Cascades Scenic Bikeway, but 

signs and pavement markings for cyclists are limited south of Estacada. At a minimum, select 

placement of W11-1 Bicycle with supplementary W16-1P Share the Road plaques will help reinforce 

the presence of bicycles on the road or shoulder. 
12

An additional option would be the use 

of dynamic warning signs (with either 

flashing LEDs or beacons) that 

become activated when bicycles are 

located within certain areas. These 

signs work by registering bicycle traffic 

counts and activating the flashing 

devices for a certain amount of time 

until cyclists have cleared an area. 

They are useful for areas where the 

shoulder is minimal and cyclists are 

within the roadway, and are especially 

useful for when cyclists can be 

expected within the roadway and there 

is limited sight distance. Potential 

locations along OR 224 for these types 

of devices would be in advance of 

select bridges (depending on shoulder width), areas where the road face extends adjacent to the inside 

of curves and limits sight distance, areas where there may be significant roadside parking and cyclists 

are pushed into traveling in the road, or to cover general areas where bicycle traffic volumes are 

anticipated to be high. These types of devices (with flashing beacons rather than LED lighting) are used 

elsewhere in Oregon, such as along OR 26, Cascade Lakes National Scenic Bikeway, and OR 242 

near McKenzie Pass (shown in Figure 3).

Parking, Pedestrians, and Adjustments to Vegetation Screen Loss

Any improvements installed within the corridor related to parking (either additions or discouragements), 

pedestrian facilities, and accommodating the loss of vegetation screens along the roadway will likely 

need to be complementary in order to provide the highest benefit. While parking is available along the 

road throughout the corridor, the areas with the highest concentration of parking will be those that 

feature an attraction and draw in overnight visitors. Vegetation screen loss causes the highest concern 

in the areas where there are campgrounds, spot camping, or environmentally-sensitive features that 

could be damaged by vehicles parking off-pavement. The areas with the highest number of parked 

vehicles will correlate directly with the highest number of pedestrians and, depending on the attraction, 

may correlate with the highest number of pedestrian crossings.

Figure 3: Dynamic Warning Sign for Bicycles (OR 242, MP 78.6, ODOT 

Digital Video Log)
13

Other federal land management agencies are 

struggling with roadside parking in undesirable 

areas. A presentation provided to Yellowstone 

National Park, detailing the known methods of 

discouraging parking in undesirable areas, is 

included in Appendix A. These methods have 

all had mixed results, though no formal study 

has ever been completed on any areas in 

which these methods have been implemented. 

Based on the different uses of the OR 224 

corridor, there will not likely be a ‘one size fits 

all’ solution. One example of an area where 

solutions to restrict parking and/or access may 

be needed is near MP 41.0, shown in Figure 

4. Visitors either park on one side of the road 

to cross to the opposite (east) side or drive 

their vehicles into traversable areas on the 

east side that are not defined as access 

driveways. In addition to the earth disturbance, 

these visitors use the hillside on the east side 

for target shooting. There is a parking area on the west side which has space for picnicking or access 

to the river. The target shooting is in range of this parking area as well as the road. While target 

shooting is a draw to the forest, this is not the most appropriate area for it and methods of further 

discouraging use in this particular area are of interest.

One method of parking discouragement discussed at the June 2021 site visit is guardrail installation. 

Guardrail is only recommended in areas where the crash as a result of a roadside departure is more 

severe than a crash caused by a vehicle striking the guardrail itself. Specific to areas of campgrounds 

or spot camping, a consideration for guardrail installation would be the clear zone width and location of 

the campers. Further discussion of guardrail and roadside design, including the clear zone, is included 

in the next section. Next steps include a review of the roadside slopes, a delineation of areas where 

parking should be discouraged, the location of the campgrounds compared to the clear zone width, and 

an analysis of the roadside condition.

Pedestrian facilities should be coordinated with both the future usage of campgrounds and the future 

context of any existing or proposed recreational facilities. Pedestrian crossings should be provided in 

any areas where parking is provided and there is some type of attraction on the opposite side of the 

road. Methods of funneling pedestrians to a defined crossing will be site-specific. The type of crossing 

will depend on both the number of anticipated pedestrian crossings and the stopping sight distance 

along the highway. Features that could be included in a pedestrian crossing may include crosswalk 

markings, advanced warning signage, in-street signage, or rectangular rapid flashing beacons. 

The next steps include a review of roadside attractions, a review of any existing and any planned or 

proposed recreational facilities, and an estimation of potential pedestrian crossings based on those 

attractions or facilities. High visibility crosswalk markings have a 48% crash reduction factor for 

potential crashes involving pedestrians (which have a high probability of resulting in a fatality); Figure 5

depicts a high visibility crosswalk example at Yellowstone National Park.. Advanced Stop/Yield for 

Pedestrians signs and markings have a crash reduction factor of 25%. Rapid flashing beacons installed 

at crossings have a crash reduction factor of 47% for crashes involving pedestrians. There is benefit to 

using more than one of these treatments at a location; for example, high visibility markings used with 

advanced signs and markings will reduce the probability of crashes involving pedestrians by more than 

48%. Crash reduction factors cited in this report are based on data or reports identified in the Crash 

Figure 4: Area of Concern for Parking and Access 

(OR 224, MP 41.0)
14

Modification Factor Clearinghouse or the AASHTO Highway Safety Manual. A crash reduction factor is 

applicable when an installed feature can reduce the risk (either in probability or in severity) of future 

crashes. Lighting and raised crosswalks may also be options.

Figure 5: High Visibility Crosswalk Markings with In-Street Signage (Yellowstone National Park; installation along OR 224 

likely not in stop-controlled areas)

Guardrail and Roadside Design

The final inventory of guardrail replaced as a result of the disaster will help guide any further efforts on 

guardrail; the preliminary accounting of anticipated guardrail replacements will have to be compared to 

the actual replacements following the logging and utility work. Once it is determined how much of the 

existing guardrail has been replaced, the next step is to determine how much of the remaining guardrail 

must be replaced to meet current crash testing criteria. Additionally, a review of the existing bridge rail 

throughout the corridor is needed.

The final step relating to guardrail is to determine how much additional guardrail is needed, based on 

new conditions following the fire. New guardrail installation will likely have to be balanced between 

relative roadside departure risk and cost. To determine where new guardrail may be warranted, a full 

evaluation of the clear zone in locations where there is no existing guardrail is recommended. A special 

focus on the areas where there has been significant vegetation loss may be needed. Once the clear 

zone and roadside slopes and actual clear zone widths are documented (compared to recommended), 

guardrail warrants can be developed. However, it is likely that there will be budgetary restrictions on 

new guardrail installation. Rather than simply developing a list of locations where new guardrail is 
15

warranted, it is recommended to develop a priority list for where guardrail and other roadside design 

treatments are most beneficial.

 

Figure 6: Apparently Undamaged Guardrail and Bridge Rail (OR 224, MP 31.2 and MP 49.97)

In other WFLHD-designed roadway projects where there are similar budgetary restrictions on guardrail 

installation or other considerations (i.e. environmental or wildlife impacts, aesthetics, etc.), WFLHD 

Safety has used a benefit/cost procedure to determine where guardrail could provide the highest value. 

Two programs available for completing this type of analysis are the AASHTO ROADSIDE procedure 

(outlined in previous additions of the Roadside Design Guide and used by the Alaska DOT&PF) and the 

Roadside Safety Analysis Program (RSAP). WFLHD Safety has used the ROADSIDE procedure 

previously. The benefits identified in these procedures are the reduction in crashes or the reduction in 

crash severities over the 20-year design life; the costs to which the benefits are compared are the initial 

construction costs of installation and the maintenance costs of repairs over the 20-year design life. 

Through the FHWA Highway Safety Improvement Program (HSIP), each state has placed a tangible, 

economic cost to different crash types; some of these costs include medical costs, property damage, 

emergency services, productivity losses, congestion impacts, insurance costs, and other legal claims. 

The opportunity to reduce these economic costs, or human impact costs, is considered to be a benefit. 

The actual costs used in these types of analysis are construction and maintenance costs, including 

potentially embankment material, guardrail, guardrail terminal sections, or vegetation clearing. 

Additionally, this analysis can identify other options that may be more cost effective than guardrail, such 

as providing full or partial clear zone treatments (i.e. find the optimized foreslope combinations and 

widths). 

Other Safety Countermeasures

The IHSDM results can help guide the placement of safety countermeasures including signage, rumble 

strips, and delineators. From the site visit on June 2021, it appeared that much of the signage 

throughout the corridor was in the appropriate location. Centerline rumble strips were present 

throughout much of the corridor, though were somewhat worn down. Delineators may have been 

common in the areas where there is existing guardrail (though it was difficult to determine due to the 

damage to the guardrail), but appeared to be less common in areas where there is no existing 

guardrail.

The next step, once a decision on previously discussed recommendations has been made, would be to 

use the IHSDM results to determine if any additional safety countermeasures are recommended. 

Examples would include:
16

• Additional curve warning signage. Depending on the type of signage, a crash reduction factor of 

25-40% is applicable for signed curves, showing a high value in areas where there is a 

significant crash history or where IHSDM has shown elevated risk.

• Additional delineators (especially in areas where guardrail has been shown not to be costeffective or where there are not sufficient funds to install guardrail). A crash reduction factor of 

11% is applicable for delineators placed on horizontal curves; there is additional benefit, though

not yet quantified, for delineators placed on tangent sections with steep drop-offs.

• High friction surface treatment (especially in areas where the curve radius or superelevation is 

deficient compared to the recommended values in the AASHTO Green Book). A crash reduction 

factor of 24% is applicable through the length of curves where high friction surface treatment is 

installed, and this treatment may have a higher benefit/cost ratio than superelevation correction 

or curve flattening. The benefit is even higher with respect to reducing crashes in wet weather.

• Wider edge lines (discussed in the bicycle section, but the highway safety benefits are present 

regardless of impacts on bicycle traffic). Wider edge lines have a crash reduction factor of 18%.

• Long-term: review crashworthiness of bridge rail throughout the corridor.

Historic crash data was reviewed and used to the extent necessary to run IHSDM, but a more thorough 

look at individual crashes and trends is needed. For the purpose of this study, the data was gathered 

and included in Appendix A (no personally identifiable information included). It is recommended that 

any future study or project complete the review of the latest crash data. A summary by severity of the 

crashes along OR 224 between 2010 and 2019 is as follows:

• 7 crashes in which the most severe outcome was a fatality (K)

• 8 crashes in which the most severe outcome was a serious injury (A)

• 37 crashes in which the most severe outcome was a moderate injury (B)

• 27 crashes in which the most severe outcome was a minor injury (C)

• 16 crashes in which the most severe outcome was property damage only (PDO)

According to the ODOT 2019 State Highway Crash Rate Tables, the crash rate for non-freeway type 

roads is 1.40 crashes per million vehicle miles traveled. Assuming 560 vehicles per day in the corridor 

over 18.8 miles, the crash rate in this corridor may be as high as 2.47 crashes per day. Given that 

traffic decreases over the length of the corridor, this may be on the low end of the crash rate.

A final consideration is emergency management. At the June 2021 project kickoff, a desire was 

indicated to investigate dynamic signage to convey messaging to the public. This messaging could 

include road closures due to slides, wildfires, or other events. It could also indicate evacuation route 

information or other critical information. The type and placement of this signage will have to be 

coordinated with both the USFS and ODOT. It will have to be determined which agency would control 

the messaging, and how they will do so. A source of power would also have to be identified.

Strategies for Improving Data Collection, Analysis and Implementation of Safety Features

FLH Safety is currently conducting a geographic information systems (GIS) and systemic safety 

research project in order to provide FLH partner agencies with better tools to supplement a lack of 

traffic and safety data as well as efficiently analyze road networks for safety improvements. The pilot 

GIS tool is available for use and can be customized for the overall studies in the entire corridor (i.e. 

from Estacada to Detroit). For example, the locations of historical and current high-use and/or 

undesirable parking areas and pedestrian activity can be captured within the GIS application. These 

efforts, along with other Forest Service efforts, could be combined to help build a robust set of data 

while the next funding phase is identified and programmed. Contact WFLHD Safety and Planning for 

more information. 
17

Other funding programs should be investigated further to identify which could be utilized to implement 

future improvements. These could include the ODOT-administered Highway Safety Improvement 

Program, the High-Risk Rural Roads Program and the All Roads Transportation Safety Program. These 

programs could help leverage FLAP, FLTP and other funding sources that ODOT and the Forest 

Service typically utilize in order to provide additional safety funding. 

Performing the analysis and further study as discussed in this Phase 1 report puts ODOT and the 

Forest Service well on the way to completing a Local Road Safety Plan, a FHWA initiative to bring 

transportation users home safely. The agencies and stakeholders in this corridor should consider 

partnering together to create a plan and strengthen ties among engineering, enforcement, education 

and emergency services countermeasures to reduce fatal and serious injury crashes. 
18

Unstable Slope Gap Analysis and On-Site Ratings Assessment

The WFLHD Geotechnical Services Team completed a review of unstable slopes along the OR 224 

corridor in order to identify data gaps and determine where there may be potentially vulnerable 

transportation assets and areas along the corridor that require more detailed unstable slope ratings 

during a Phase 2 Corridor Master Plan. A comprehensive assessment is included as Appendix B –

Unstable Slope Gap Analysis and On-Site Ratings Assessment Final Memorandum.

Corridor Geology

The OR 224 corridor study area lies entirely within the Western Cascades Physiographic Province, 

which is characterized by older volcanic rocks, generally steep slopes, and large pre-historic (ancient) 

landslide deposits (Peck, et al., 1964; see Figure 7). There are four bedrock units that underlie the 

corridor, and all are approximately horizontally bedded. The oldest and lowest in position are 

sedimentary and volcaniclastic rocks of the Little Butte Volcanic Series (approximately 23 to 33.9 

million years ago (Ma)) located in the upper reaches of the Clackamas River, from Three Lynx Creek at 

MP 45.87 to the end of the corridor at the intersection of FSR 57. This unit is primarily composed of 

volcanic and volcaniclastic deposits, including volcanic tuffs, mudflows, and lava flows of basalt and 

andesite. Smith (1994) indicates that the unit consists of “clay-bearing volcaniclastic formations overlain 

by unaltered lava flows of andesite and basalt, a combination that contributed to large-scale landsliding 

during the late Pleistocene”, approximately 10 thousand years ago (Ka). The entire valley bottom 

contains large scale earthflow-type landslides that produce generally subdued topography as compared 

to the lower portion of the corridor.

Overlying the Little Butte Volcanic Series are the Grand Ronde and Wanapum members of the 

Columbia River Basalt Group (approximately 15 to 17 Ma). These lava flows form steep cliffs along the 

Clackamas River from the beginning of the corridor at the Mount Hood National Forest Boundary up to 

Three Lynx Creek. The basalt lava flows are generally resistant to erosion and form steep cliffs. 

However, there is a weak sedimentary interbed called the Vantage Member between the two lava 

flows. The Vantage Member is composed of ashy, volcanic sandstone and siltstone deposits and is a 

barrier to groundwater flow, resulting in increased pore-water pressure at the slope face where the unit 

is exposed. The resulting pore water pressure in some cases has created slope instability where large 

landslides occur. The Vantage Member typically forms a steep bench of loose, unconsolidated talus 

where the upper basalt flows have been removed by undercutting.

Immediately above the Columbia River basalts are interfingered (layered) deposits of the 

Rhododendron and Sardine Formations (approximately 10 to 17 Ma), which are composed of 

volcaniclastic deposits of mudflows, conglomerates, and ash tuffs, as well as basalt and andesite lava 

flows, respectively. These geologic units cap the ridges within the corridor, including Wanderer’s Peak, 

Soosap Peak, Fish Creek Mountain, and East Mountain. The material in the Rhododendron formation is 

easily eroded and is also prone to landsliding, which occasionally initiates as debris flows in the steep 

tributaries of the aforementioned peaks into the Clackamas River.

Overlying the Rhododendron and Sardine Formations are younger basaltic and andesitic volcanic lava 

flows of the High Cascades (approximately 1.2 to 3.9 Ma). These geologic units are primarily found in 

the headwaters of tributaries of the Clackamas River East of the corridor, and generally cap the ridge 

tops, including Mount Mitchell and Oak Grove Butte.

Also within the corridor is a wide plateau known as “La Dee Flat”, north of the Clackamas River at 

Promontory Park. La Dee Flat has a low slope angle that generally precludes the development of 

landslides.
19

Figure 7: Geologic Map of the area of the Highway 224 corridor impacted by the Riverside Fire (modified from Peck, et al., 1964)
20

Site Conditions

Lower Corridor – Forest Boundary to Three Lynx Creek

Loss of vegetation from the fire has destabilized talus slopes on benches as well as on alluvial fan 

deposits along the base of the Columbia River basalts in the lower portion of the corridor. Increases in 

rockfall have occurred and should be anticipated to continue along the corridor from the Forest 

boundary to Three Lynx Creek. Additionally, debris flow potential exists where easily erodible deposits 

of Rhododendron formation overlie steep valley walls of Columbia River basalt. Modelling results 

provided by the U.S. Geological Survey (USGS) (Staley and Kean, 2020) indicate that streams crossing 

the highway in this section of the corridor are generally at moderate to high hazard for debris flows.

Upper Corridor – Three Lynx Creek to FSR 57

Increases in soil moisture related to a decrease of evapotranspiration from a loss of vegetation has the 

potential to reinitiate and/or accelerate earthflows in the upper portion of the corridor from Three Lynx 

Creek to FSR 57, although this is anticipated to be minor over the course of the next five to ten years 

as vegetative cover increases. This has the potential to lead to increased deformation and subsidence 

of the paved surface of the roadway. Additionally, increased surface runoff on the earthflows could lead 

to significant erosion and sedimentation, which would negatively impact transportation infrastructure 

(roads, ditches, culverts). Streams draining this area are generally at a low hazard for debris flows 

(USGS, 2020).

Analysis Method

This analysis was conducted as a desktop exercise that relied exclusively on existing data to identify 

two classes of unstable slopes:

1. Unstable slopes with ratings and/or assessments

2. Unstable slopes, or potentially unstable slopes without ratings and/or assessments

The intent was to identify vulnerable transportation assets and identify areas along the corridor that 

require more detailed unstable slope ratings or condition assessments during the Phase 2 Corridor 

Master Plan. The analysis relied primarily on two existing data sources:

1. Oregon Department of Transportation’s (ODOT) Unstable Slope Rating System (USRS) 

database

2. USGS’s Emergency Assessment of Post-Fire Debris-Flow Hazards debris flow modelling

ODOT’s USRS analyzes slopes adjacent to state highways for potential impacts that a failure could 

cause. Such failures include landslides, rockfall, and fill settlement or failures. Historically, ODOT has 

evaluated rock fall hazards, but has expanded the program to include other (soil) types of unstable 

slopes (landslides and debris flows). Under the revised program, ODOT is able to include economic 

factors in its analysis as well as hazard and engineering considerations so that sensible repair priorities 

can be more easily obtained.

The USGS conducts post-fire debris-flow hazard assessments for select fires in the Western United 

States, utilizing geospatial data related to basin morphology, burn severity, soil properties, and rainfall 

characteristics to estimate the probability and volume of debris flows that may occur in response to a 

design storm event.

This analysis attempts to identify locations of debris flow prone unstable slopes or areas where debris 

flows could occur and are lacking unstable slope rating or site condition assessment data. These areas 

are clearly delineated where no unstable slope rating data exist and USGS modelling identified 

channels at moderate to high hazard for debris flow initiation. For this effort, we focused on stream 
21

channels that exhibited channel morphology (geology, grade, length, depth of incision, coalescing fan 

deposits, levies, anastomosing channels, etc.) and observed past debris flow events that supported 

potential for future debris flow events. If channels met those criteria, based on geo-practitioner 

judgment, a recommendation to rate the unstable slopes was made. If the channel met the above 

criteria, but did not include observation of past debris flow events, a recommendation to perform a site 

condition assessment was made.

This analysis assumes that potentially unstable slopes that have not been assessed and rated by 

ODOT will be assessed and rated utilizing the Unstable Slope Management Program for Federal Land 

Management Agencies (USMP, FLH 2019) in Phase 2. In order to combine data from the two systems, 

and be useful in a geotechnical asset management framework, a crosswalk between the rating systems 

must be established so that ranking of sites can be accomplished utilizing ratings from either system. 

The crosswalk would assist in an “apples to apples” comparison of ratings so that sites can be ranked 

and prioritized for potential risk reduction measures. Therefore, a sample of unstable slopes in the 

corridor, rated utilizing the USRS, should be rerated with FLH’s USMP prior to the rating of new 

unstable slopes utilizing the USMP. Rerating of ODOT USRS rated unstable slopes should include a 

range of different unstable slope types (landslide, rockfall, debris flow, etc.) from a low to high risk, and 

should focus on slopes that include a STIP score, which is the score used for project identification and 

prioritization for ODOT. This additional level of effort is strongly recommended for the Phase 2 Corridor 

Master Plan.

Analysis Results

ODOT’s USRS consists of 45 pre-fire unstable slope ratings conducted between 2007 and 2009, as 

well as 42 post-fire assessments (non-ratings) completed in 2020, which included 13 new unstable 

slope assessments that did not have a rating associated with them. The post-fire assessments 

reassessed 30 (67%) of the pre-fire unstable slopes, for a total of 58 ODOT pre and post-fire ratings 

and/or assessments of unstable slopes within the study corridor. Pre-fire unstable slope ratings 

included 30 rockfall sites, 14 road fill failures, and five landslides. The new slope assessments focused 

primarily on rockfall (see Attachment 2 - Unstable Slopes Existing Condition and Data Gaps Maps, and 

Attachment 3 - Table of Unstable Slopes with USRS Ratings).

The USGS modeled debris flow hazard for 84 streams that intersect the highway within the study 

corridor, which ranged from low to high (see Attachment 2 - Unstable Slopes Existing Condition and 

Data Gaps Maps in Appendix B). Generally, streams in the lower corridor were modelled as moderate 

to high hazard, while streams in the upper corridor were modelled as low to moderate hazard. This is 

interpreted as being controlled by the presence of differing geology and the associated basin 

morphology between the upper and lower corridor.

Lower Corridor – Forest Boundary to Three Lynx Creek

ODOT identified and rated 41 unstable slopes in the lower corridor. Communication with ODOT 

identified four unstable slopes that were not assessed in the post-fire effort but would benefit from 

completing a more detailed rating. The USGS modeled 73 stream segments for debris flows hazard in 

the lower corridor, and 37 (51%) were rated at high hazard, 34 (47%) moderate hazard, and 2 (3%) low 

hazard. Analysis of unrated, debris flow prone channels identified two unstable slopes that should also 

be rated, and eight sites where condition assessments should be performed.

Upper Corridor – Three Lynx Creek to FSR 57 

ODOT identified and rated ten unstable slopes in the upper corridor. Communication with ODOT 

identified four unstable slopes that were not assessed in the post-fire effort but would benefit from 

completing a more detailed rating. There is a lack of slope ratings in the upper section of the corridor, 

which may indicate that there is minimal geologic hazard present in this area due to the generally 
22

subdued topography. The USGS modelled 13 stream segments for debris flows hazard in the upper 

corridor and had generally low to moderate hazard. Analysis of unrated, debris flow prone channels 

identified one unstable slope that should also be rated.

Unstable Slope Assessment Recommendations

Following the desktop analysis of existing data, the WFLHD Geotechnical Services Team identified 

three recommendations to address unstable slope risk along the OR 224 study area:

• Conduct a crosswalk of USRS rated unstable slopes by rerating both types of unstable slope 

with the USMP in order to compare ratings between the two systems so that sites can be 

ranked and prioritized for potential risk reduction measures. 

• Utilize the USMP; (FLH, 2019) to rate identified unstable slopes where data gaps exist. This 

includes eight sites recommended by ODOT, three high hazard debris flow channels where past 

debris flow events have been observed, and the approximately five miles of the upper corridor 

from Three Lynx Creek to FSR 57 (see Attachment 4 - Table of Unstable Slopes Requiring 

USMP Ratings or Site Condition Assessments in Appendix B). 

• Additionally, perform site condition assessments on eight high hazard debris flow prone 

channels where past debris flow events have not been observed. These data could be used to 

inform future study efforts that identify project-specific improvements to make OR 224 a more 

resilient transportation corridor.
23

Hydrology Gap Analysis

This section provides a hydrologic and hydraulic corridor assessment of the OR 224 study area. The 

assessment identifies available data, evaluates the suitability of the data, and identifies data or 

information gaps to be addressed in future study efforts. A desktop review of available post-fire reports, 

as-built information, maintenance/inspection data, basin maps, and U.S. Geological Survey (USGS) 

post fire debris flow hazard mapping was conducted by the WFLHD Hydraulics Team to identify 

drainage structures, flood and debris flow prone areas, transportation infrastructure, and facilities which 

may be impacted by post fire flows through and downstream of the corridor. A comprehensive analysis

is included as Appendix C – Hydraulics Data Gap Analysis Final Memorandum.

Available Data and Suitability

The USFS Rapid Assessment Team evaluated the fire and completed a report, dated October 2020, 

which provided basal area mortality maps, summarized conditions, and provided action 

recommendations. A Burned Area Emergency Response (BAER) team began work on assessing the 

post-fire effects in September 2020. The team developed reports that include comprehensive 

information which will support the OR 224 corridor assessment.

Burned Area Reflectance Classification (BARC), aerial reconnaissance data, and on-the-ground 

surveys were conducted to develop a Soil Burn Severity (SBS) map which was used to estimate the 

soils post-fire hydrologic responses and resulting flows for the Clackamas River subwatersheds. Risk of 

upland erosion, sedimentation delivery rates, and increased flood flows were then estimated for 27 

subwatersheds using the Water Erosion Prediction Project (WEPP) Post-Fire Erosion Predictor (PEP). 

This was compared to pre-fire 5-year recurrence interval flood conditions to identify levels of risks at 

road/stream crossings. The BAER report provides analysis results of crossing points along OR 224 

listed in Table 5. Significant increase in flow are predicted for a majority of the analyzed crossings.

Table 5: 2020 BAER Report Crossing Points

Crossing Points Pre-fire

Q5 (cfs)

Post-fire

Q5 (cfs)

%

Increase

Times

Increase

Pre-fire

Q50 (cfs) Acres

Moore Creek 380 390 3% 1.0X 530 459

Unnamed Tributary 110 240 118% 2.1X 340 171

Murphy Creek 180 250 39% 1.3X 270 257

Unnamed Creek 99 190 92% 1.9X 170 133

Three Lynx Bridge 340 590 74% 1.7X 1,300 1,675

Deer Creek 140 270 93% 1.9X 320 200

Dinner Creek 430 680 58% 1.5X 1,200 921

Roaring River 7,400 8,300 12% 1.1X 15,000 27,229

The burn area mortality, soil burn severity, subwatershed, and subwatershed peak stream flow analysis 

point maps developed by the BAER team have been included in Appendix C.

The USGS conducted a post-fire debris-flow hazard assessments using the post-fire data and 

developed mapping. They utilized geospatial data related to basin morphology, burn severity, soil 

properties, and rainfall characteristics to estimate the probability, volume, and combined hazard rating 

of debris flows at both the drainage-basin scale and in a spatially distributed manner along the drainage 

network within each basin. The debris flow hazard mapping can be found on the following USGS 
24

website which includes downloadable shapefiles and geodatabase information: 

(https://landslides.usgs.gov/hazards/postfire_debrisflow/detail.php?objectid=309)

The USGS model identifies 84 streams that intersect the highway within the study corridor. This 

includes those crossing points listed in Table 5. Due to differences in geology and basin morphology, 

the 73 streams modelled in the lower corridor between the forest boundary and Three Lynx Creek rated 

as moderate to high hazard. The 13 streams modelled in the upper corridor from Three Lynx Creek to 

Forest Road 57 rated as low to moderate hazard.

Within the lower corridor there were 37 stream intersects that rated as high hazard. Although a handful 

of these where points modeled for flow in Table 5, additional flow modeling for the remaining crossings 

were not performed or unavailable.

The Oregon Department of Transportation (ODOT) was able to provide data on crossing structures for 

a portion of the lower corridor from the forest boundary to Mile Point (MP) 36 just south of Moore Creek. 

Beyond this point ODOT did not have inspection data for crossing structures, but only had culverts 

listed on plans. Since ODOT restricts outside access to their GIS database, the data provided was in 

spreadsheet format with information limited to specified queries. Additional asbuilt, inspection, and 

maintenance data for culverts along the corridor are available from the USFS. Per discussions with 

USFS staff, this data would need to be obtained from isolated databases and possibly from multiple 

sources. Current post-fire inspection information for crossing structures was not available. 

ODOT provided asbuilt plans and inspection reports, in electronic pdf format, for all bridges within the 

corridor which are listed in Table 6. The table does include three large culverts (Bull Creek, NF 

Clackamas, and Dry Creek) that fall within the recording requirements of the National Bridge Inventory 

System (NBIS).

Table 6: Bridges along the OR 224 Corridor with Asbuilt Plans and Inspection Reports

Bridge No. Mile Post Description Scour Critical

Rating

18178 41.48 Roaring River Bridge

18619 47.70 Bull Creek Culvert

05269 49.96 Clackamas River (Oak Fork Ripple Brook Br) 3

05272A 30.04 North Fork Clackamas River (Steel Plate Culvert)

08988 38.77 Clackamas River (Carter Br)

08989 39.15 Clackamas River (Armstrong Br) 3

08990 45.83 Clackamas River (Cripple Creek Br) 3

08991 44.88 Clackamas River (Three Lynx/Whitewater Br) 3

08992 49.12 Dry Creek Culvert

Review of the inspection reports revealed that four (4) of the bridges within the corridor have a NBIS

scour critical rating of 3. This means that these structures’ foundations have the potential to be 

undermined by stream scour or erosion. The expected post-fire changes in flow conditions, debris 

loads, and sediment loads have the potential to increase scour and erosion resulting in a higher risk for 

the bridges becoming unstable.

ODOT performed inspections of the bridges along the corridor in August of 2019. Another inspection is 

scheduled for this year. Inspection photos are available within the ODOT GIS database and can be 

provided upon request but would need to address large file transfer requirements.
25

In addition to the analysis and recommendations included in the USFS BAER team reports, ODOT 

requested that the Federal Emergency Management Agency’s Erosion Threat Assessment/Reduction 

Team (ETART) produced a separate report to assess State, local, and private lands outside of the 

forest. This report re-affirms much of the recommendations made by the BAER team, but also adds 

recommendations for property and facilities affected downstream of the forest boundary.

Corridor Needs and Data Gaps

After review of available data and related report recommendations, the following hydrologic and 

hydraulic related needs and data gaps have been identified for the OR 224 corridor.

Roadway Drainage and Culverts

ODOT is currently removing debris, removing danger trees, and storm proofing (cleaning ditches, 

culverts, repairing drainage) along the corridor to address immediate hazard concerns. However, 

hazardous conditions will continue to develop over the next 5 years as the loss of vegetation will allow 

normal storms to more easily cause erosion and debris flows on the steep roadside slopes resulting in 

further plugging of ditches and culverts, and/or washouts of drainage facilities or stream crossings. The 

BAER and ETARTS reports recommend a number of drainage and culvert related actions to address or 

help reduce impacts from these expected hazards during the period in which vegetation recovers.

A prioritized mitigation action plan should be prepared that identifies the most susceptible drainage 

crossings impacted by increased flow and debris. Pre-fire and post-fire flow modeling has been 

performed on only a small number of crossings (see Table 1) within the corridor. Flow modeling of 

additional crossings would assist in identifying culverts that may now be undersized or less able to 

accommodate plugging. Modeling may involve pre-fire and post-fire flow analysis or just post-fire 

regression flow analysis. Crossings located at high and/or moderate debris flow potential sites should 

also be evaluated to determine the resulting risk and hazard that debris flows may have at each site.

Creating a complete inventory of drainage structures within the corridor (including condition 

assessments, documented maintenance issues, fish barrier issues, and geographic reference data) will 

be needed to produce a comprehensive mitigation plan and conduct flow analysis. This effort will also 

help identify structures needing to be replaced (specifically within the next 5-years), identify sites that 

may be more prone to debris/plugging, and assist crews in locating structures in the field. Conducting 

site specific field evaluations may also be needed to begin identifying and prioritizing mitigation actions. 

Mitigation actions may include, but are not limited to, the following:

• Culvert replacements or modifications to increase capacity (replacements should be sized on 

predicted increase in flows or fish passage requirements).

• Installation of additional culverts at high risk locations.

• Placement of upstream structures to deflect or catch debris away from the roadway.

• Installation of slotted riser pipes, debris racks, and culvert end sections where feasible to reduce 

sediment and debris plugging.

• Roadway embankment armoring in areas at risk for overtopping.

• Drainageway improvements at crossings to reduce or eliminate streamflow diversion potential.

Bridges

Post fire flow analysis indicates that increases in flow along the lower Clackamas River may not have a 

significant impact on bridges along the OR 224 corridor. Over the next 5 years, significant amounts of 

eroded fine sediment will be deposited in draws, stream and river channels, and floodplains. This 

increased loading can result in aggradation and channel migration at bridges. Large woody debris will 

also accompany the initial flush of fine sediments and ash that is delivered to bridges along the corridor 

during high-intensity rain events over the next 5-years. This will greatly increase potential for debris 
26

jams to form around bridge abutments leading to significant increases in the potential for scour to 

undermine piers and abutments. Debris flow potential from Fish Creek and smaller drainages adjacent 

to the bridges may also impact the flow patterns at bridge crossings which can lead to increases in 

erosion and scour.

It will be important to perform a post-fire evaluation of the four bridges rated as scour critical. Evaluation 

of the remaining bridges may also be warranted. The level of risk posed by increased debris jams, 

changes to flow patterns, aggradation, and channel migration should be re-evaluated. The evaluations 

will require collecting pre-fire and post-fire photos, measuring channel conditions, identifying existing 

scour counter measures, and documenting scour conditions near abutments and piers. This information 

will not only be useful in evaluating the risk but will allow inspectors to identify changing conditions 

more readily after significant storm events.

Identification and prioritization of additional site-specific monitoring efforts and preventative measures 

should consider the following:

• Increasing bridge inspection intervals.

• Additional emergency storm monitoring and response plans.

• Post-storm scour, damage, and debris inspection and assessment.

• Installing additional scour countermeasures.

• Monitoring movement of large woody debris and debris removal plans.

• Installation of real-time water surface elevation and/or scour monitoring devices to alleviate staff 

limitations.

• Signing and temporary emergency closure plans.

Facilities and Properties

The WFLHD review teams identified a high risk to Get-N-Go Promontory Marina and North Fork 

Reservoir Dam from woody debris build up. Increasing inspection frequency will be needed to identify 

debris removal. Staging, storage, and disposal areas will need to be identified and coordinated. 

The primary access to the Portland General Electric (PGE) Oak Grove Powerhouse is also vulnerable 

to debris flow from Three Lynx Creek. Mitigation actions that could be considered for this location could 

include placement of upstream debris racks, additions culverts, or armoring of the roadway. 

Additionally, an emergency response and access plan should be developed in coordination with PGE.

Water Supply

The Riverside Fire burned a large part of the municipal watershed of the City of Estacada and has the 

potential to impact other downstream municipal water supplies that have intakes on the Clackamas 

River including City of Lake Oswego, Clackamas River Water, Clackamas Water District, North 

Clackamas County Water Commission, and South Fork Water Board municipalities.

During and after high-intensity storms, turbidity, dissolved organic carbon, nitrate, and some metals 

may likely increase by large magnitudes downstream of the burned area. Increases of such magnitude 

can pose problems for water-supply reservoirs and drinking-water treatment plants that can last many 

years and affect chemical treatment requirements, sludge volumes, and operating costs. 

Starting coordination with the affected municipalities to assess capacity of facilities to address post-fire 

water quality will assist in identifying if additional water quality monitoring within Clackamas River is 

needed to help managers. This could provide data to better estimate affects to operations and allow 

them to minimize effects through temporary diversions or changes to water intakes.
27

Watershed

The ETARTS team recommends installation of one or more near real-time (NRT) precipitation gages in 

or near the burn area. A NRT gage provides invaluable information about the localized intensity and 

amount of precipitation as it happens. Based on these data, the National Weather Service (NWS) can 

issue alerts to emergency managers, road crews, and other partners to warn of increased potential for 

flooding and debris flows that could threaten lives or damage homes, roads, and other infrastructure. 

Further developing gaging station data with rainfall data relations can assist with future evaluations of 

post-fire flood magnitude and hydrologic response in ungaged.

The specific locations for possible NRT gages and funding sources will need to be evaluated and 

coordinated between agencies.

Hydrology Assessment Recommendations

The following summarizes recommended actions that will assist in completing data or information gaps 

for future study efforts in identifying project-specific improvements:

• Develop a comprehensive drainage crossing inventory that includes post-fire condition 

inspections, emergency maintenance history, fish barrier information, and georeferenced 

location mapping.

• Conduct detailed post-fire hydrologic and hydraulic analysis on identified elevated risk 

crossings.

• Conduct site specific field evaluations of crossings affected by significant increased flow and 

within high risk debris flow areas.

• At bridge crossings, collect pre-fire and post-fire photos, measure channel conditions, identify 

existing scour counter measures, and documenting scour conditions at abutments and piers.

• Perform post-fire site evaluations for increased scour and erosion risks at bridges within the 

corridor (most importantly bridges rated as scour critical)

• Identify the number of locations potential NRT gages would need to be installed to provide 

useful emergency response data.

• Assist municipalities in assessing water supply facility capacities to address post-fire water 

quality and any needs for additional water quality monitoring.

Future Study Efforts

Creating an effective and efficient mechanism to implement, monitor, evaluate, and report on recovery 

activities, emergency responses, updates, and progress will require establishing staff roles, 

responsibilities, funding sources, and contact information across agencies.

Corridor drainage structure data should be organized in a format that can be readily accessed and 

shared by multi-agency staff involved in the implementation. Data must also be geographically 

referenced, easily visualized, relevant, and up to date. Control of the data and necessary data sharing 

activities will need to be clearly defined.

Once all hydrologic and hydraulic drainage data has been collected and relevant analysis has been 

performed, preventative mitigation measures will need to be identified and prioritized at all high-risk 

roadway drainage crossings and bridges.

Throughout the vegetation recovery period, storm patrols will need to be conducted to monitor road 

drainage ditches, culverts, debris control structures, and bridges during and after significant rainfall 

events to ensure that structures remain safe and functioning at maximum capacity. A storm patrol plan 

and notification system will need to be developed and should be coordinated with other agencies 

accessing the corridor, including USFS, Clackamas County, Portland General Electric and ODOT.
28

Agencies will also need to be establish an emergency maintenance plan. They should be prepared to 

provide significant maintenance efforts after storm events to remove sediment and debris from ditches 

and entrances to culverts. Addition removal of debris flow material from the roadway and repair of the 

roadway may also be needed. The emergency maintenance plan should address key components such 

as before, during, and post-storm activities, priorities, and responsibilities. The plan should identify 

staging, storage, disposal areas for heavy equipment, materials, and removed debris.

Summary of Technical Recommendations and Areas of Further Study

The following sections summarize the technical recommendations and areas of further study to improve 

the wildfire-impacted, closed section of the OR 224 corridor.

Traffic and Safety Phase 1 Recommendations

Bicycle Facilities

• When visitation has normalized, conduct traffic counts to better understand seasonal traffic data 

(including bicycles), especially to understand the post-disaster differences in use throughout the 

corridor from the pre-disaster conditions. Many of the recommendations will be dependent on

this data. The Forest should also coordinate with ODOT and WFLHD to identify traffic count 

needs to the south of the ODOT-maintained highway.

• Determine appropriate locations for additions of W11-1 Bicycle with supplementary W16-1P 

Share the Road plaques.

• Determine feasibility of dynamic warning signs (with either flashing LEDs or beacons) that 

become activated when bicycles are located within certain areas.

• Determine feasibility of wider edge lane markings (requires coordination with ODOT).

• Long-term: determine if shoulder widening is feasible or desired to provide 4- to 5-foot shoulders 

throughout the entire corridor.

Parking, Pedestrians, and Vegetation Screen Loss

• Determine locations where parking is undesirable and determine (from Appendix C, or from any 

other found sources) potential treatments to help discourage parking in those areas.

• Determine, in coordination with any potential planned recreational facility additions or upgrades 

and with consideration of any attractions or overnight visitation areas, where pedestrian 

crossings are most likely. Based on the availability of parking or the popularity of the attractions 

or overnight visitation areas, estimate the number of daily pedestrian crossings. 

• Based on B above, determine the appropriate treatments at planned pedestrian crossings. 

Options include crosswalk markings, advance signage and markings, and rapid flashing 

beacons. If there is to be a major crossing, lighting may also be considered, but it is probable 

that such a major crossing does not exist in this corridor. Raised crosswalks are another option, 

though the impacts on maintenance and traffic must be considered.

Guardrail and Roadside Design

• Review the final inventory of replaced guardrail. 

• Determine the amount of remaining existing guardrail (including terminal sections) that must be 

upgraded in order to meeting current crash testing criteria.

• Determine the actual clear zone throughout the corridor.

• Determine a priority list of placement of new guardrail. A benefit to cost procedure, discussed 

previously in this report, is likely necessary in order to determine the locations of highest value 

of new guardrail placement.
29

• Where guardrail may be warranted but cannot be installed due to lack of funding or other 

considerations, review other safety countermeasures (below) for alternatives.

Other Safety Countermeasures

• Once a determination has been made on recommendations for bicycles, parking, pedestrians, 

vegetation screen loss accommodations, guardrail, and roadside design, consider any 

remaining safety countermeasures that may be needed either to account for other risks or to 

account for any recommendations that could not be implemented due to cost or other 

considerations.

o This includes but is not limited to curve warning signage, delineators, and high friction 

surface treatment.

• Complete review of historic crash data (see Appendix A).

• Determine feasibility of installation of dynamic signage for emergency management. The type, 

location, and control will have to be coordinated between USFS and ODOT.

Strategies for Improving Data Collection, Analysis, and Implementation of Safety Features

FLH Safety is currently conducting a GIS and systemic safety research project in order to provide 

FLH partner agencies with better tools to supplement a lack of traffic and safety data as well as 

efficiently analyze road networks for safety improvements. The pilot GIS tool is available for use 

and can be customized for the overall studies in the entire corridor (i.e. from Estacada to Detroit). 

For example, the locations of historical and current high-use and/or undesirable parking areas and 

pedestrian activity can be captured within the GIS application. These efforts, along with other Forest 

efforts, could be combined to help build a robust set of data while the next funding phase is 

identified and programmed. Contact WFLHD Safety and Planning for more information. 

Other funding programs should be investigated further to identify which could be utilized to 

implement future improvements. These could include the ODOT-administered Highway Safety 

Improvement Program, the High-Risk Rural Roads program and the All Roads Transportation 

Safety program. These programs could help leverage FLAP, FLTP and other funding sources that 

ODOT and the Forest typically utilize in order to provide additional safety funding. 

Performing the analysis and further study as discussed in this memorandum puts ODOT and the 

Forest well on the way to completing a Local Road Safety Plan, a FHWA initiative to bring 

transportation users home safely. The agencies and stakeholders in this corridor should consider 

partnering together to create a plan and strengthen ties among engineering, enforcement, 

education and emergency services countermeasures to reduce fatal and serious injury crashes. 

Unstable Slope Phase 1 Recommendations

• Conduct a crosswalk of USRS rated unstable slopes by rerating both types of unstable slope 

with the USMP in order to compare ratings between the two systems so that sites can be 

ranked and prioritized for potential risk reduction measures. 

• Utilize the USMP; (FLH, 2019) to rate identified unstable slopes where data gaps exist. This 

includes eight sites recommended by ODOT, three high hazard debris flow channels where past 

debris flow events have been observed, and the approximately five miles of the upper corridor 

from Three Lynx Creek to FSR 57 (see Attachment 4 - Table of Unstable Slopes Requiring 

USMP Ratings or Site Condition Assessments in Appendix B). 

• Additionally, perform site condition assessments on eight high hazard debris flow prone 

channels where past debris flow events have not been observed. These data could be used to 

inform future study efforts that identify project-specific improvements to make OR 224 a more 

resilient transportation corridor.
30

Hydrology Phase 1 Recommendations

• Create an effective and efficient mechanism to implement, monitor, evaluate, and report on 

recovery activities, emergency responses, updates, and progress, which will require 

establishing staff roles, responsibilities, funding sources, and contact information across 

agencies.

• Organize corridor drainage structure data in a format that can be readily access and shared by 

multi-agency staff involved in implementation. Data must also be geographically referenced, 

easily visualized, relevant, and up to date. Control of the data and necessary data sharing 

activities will need to be clearly defined.

• Once all hydrologic and hydraulic drainage data has been collected and relevant analysis has 

been performed, preventative mitigation measures will need to be identified and prioritized at all 

high-risk roadway drainage crossings and bridges.

• Throughout the vegetation recovery period, storm patrols will need to be conducted to monitor 

road drainage ditches, culverts, debris control structures, and bridges during and after 

significant rainfall events to ensure that structures remain safe and functioning at maximum 

capacity. A storm patrol plan and notification system will need to be developed and should be 

coordinated with other agencies accessing the corridor, including USFS, Clackamas County, 

Portland General Electric and ODOT.

• Agencies will also need to be establish an emergency maintenance plan. They should be 

prepared to provide significant maintenance efforts after storm events to remove sediment and 

debris from ditches and entrances to culverts. Addition removal of debris flow material from the 

roadway and repair of the roadway may also be needed. The emergency maintenance plan 

should address key components such as before, during, and post-storm activities, priorities, and 

responsibilities. The plan should identify staging, storage, disposal areas for heavy equipment, 

materials, and removed debris.
30

Phase 2 - OR 224 Corridor Master Plan Scoping

The Phase 1 Existing Conditions Assessment offers a baseline understanding of the wildfire-impacted 

OR 224 corridor as it exists today. The report is intended to expand upon other post-fire assessments 

that have been completed, including the 2020 BAER report. While these baseline assessments offer 

valuable insights into current conditions, a comprehensive forward-thinking corridor master plan is 

needed to determine the future vision of the corridor, clearly articulate the complexity of transportation 

needs, and begin identifying alternatives and specific projects that will help achieve the corridor vision.

Proposed Work Summary 

The proposed Phase 2 – OR 224 Corridor Master Plan will develop a comprehensive planning 

document that examines the current and future conditions and needs of the wildfire-impacted corridor. 

A master planning process will be especially useful in this particular context, as the future needs of the 

OR 224 corridor have not yet been defined and there are other related planning efforts in progress 

(e.g., viewshed planning, facility management, and recreational planning) that can be leveraged. The 

2020 Riverside Fire completely changed the landscape within the Mount Hood National Forest 

Clackamas River Ranger District, impacting over 138,000 acres of land and various recreational sites. 

The challenges of recovering from wildfires are evident, particularly when disaster relief resources are 

limited, and these challenges are compounded without a clear roadmap of prioritized improvements.

The closed-portion of OR 224 from Promontory Park and Ripplebrook (MP 31.2 to MP 49.9) served a 

multitude of uses prior to the 2020 Riverside Fire, including timber management, hydroelectric power 

transmission, regional drinking water treatment, technical career training, and outdoor recreation. This 

planning effort will help develop a long-term, coordinated vision and related goals for the impacted 

area, further investigate high risk areas along the corridor, develop initial site designs for transportation 

improvements, and identify a comprehensive suite of capital projects and policy recommendations that 

support the many uses of the Mount Hood National Forest while enhancing transportation access.

High-Level Phase 2 Master Plan Scope

To assist the USFS and ODOT in pursuing additional funding resources to improve transportation 

access for OR 224, a high-level scoping framework and project budget have been developed.

Task 1 – Project Coordination, Communication and Management Plan and Kick-Off Meeting

The foundation of any successful project lies in a strong project roadmap. A productive kick-off meeting 

and thoughtful project work plan are essential in establishing that roadmap, which will outline the key 

project goals, procedures including a public involvement strategy, and a comprehensive work schedule 

and action tracker to maintain momentum throughout project delivery. Key activities for Task 1 may 

include:

• Compiling data and reports not collected in the Phase 1 Corridor Study Existing Conditions 

Assessment

• Developing a Public Involvement Strategy to guide the Corridor Master Plan process

o This will serve as a framework for obtaining stakeholder input on project issues and 

options to inform the project decision process. 

o The strategy document shall:

▪ Identify stakeholders

▪ Describe approaches and techniques to involve stakeholders

▪ Identify methods to gather and address stakeholder input

▪ Describe methods for evaluating effectiveness of outreach efforts

▪ Document the implementation of the Public Involvement Strategy

• Develop detailed project schedule
31

• Develop Project Coordination, Communication and Management Plan (this will describe final 

scope, schedule and budget for the Corridor Master Plan and serve as the project roadmap)

Task 2 – Community Visioning, Goal Setting and Public Engagement Strategy

Community visioning and goal setting offer residents, businesses, local institutions, and other 

stakeholders an opportunity to express their ideas about the future of their community and identify 

benchmarks to work towards. To effectively engage local stakeholders, a comprehensive and strategic 

public engagement approach must be developed. Key activities for Task 2 may include:

• Create a public-facing project website, which will be updated occasionally throughout the 

Corridor Master Plan with draft deliverables and information on opportunities to provide 

feedback.

• Establish a Project Advisory Committee (PAC) and host PAC meetings on a regular schedule.

• Develop a project contact list of interested parties.

• Develop news releases and project newsletters.

• Public meetings during the Corridor Master Plan – plan, coordinate, and attend approximately 3 

public meetings. General topics for each meeting include:

o 1st Public Open House – Identify Corridor Vision, Goals and Transportation Needs

o 2nd Public Open House – Present Solutions and Recommendations for Stakeholder 

Consideration

o 3rd Public Open House – Draft Corridor Master Plan

Task 3 – Finalize Existing Conditions Assessment, Define Desired Future Conditions, and 

Investigate Corridor Management Strategies

Various existing conditions data and assessments have been compiled for the closed OR 224 route, 

including data required to begin disaster recovery that was captured in the 2020 BAER Report and 

additional corridor-specific analyses included in this Phase 1 Existing Conditions Report. There are still 

data gaps that remain, documented in prior sections of this report, and should be included in any future 

planning analyses. To wrap-up the OR 224 Existing Conditions Assessments and define desired future 

conditions, the following Task 3 activities should include:

• Review and complete the areas of further analysis for traffic operations, safety, unstable slope 

ratings, and hydrology as identified in this Phase 1 report.

• Review and clarify existing right-of-way, maintenance, and operations agreements for the 

corridor.

Task 4 – Needs Identification and Alternatives Development

Using the stakeholder and public input received in Task 2 and the existing and desired future conditions 

gathered in Task 3, the USFS and ODOT can begin to identify specific corridor transportation needs 

along OR 224 and identify a range of system alternatives for consideration. Needs identification shall 

be based on both qualitative (input received during the 1st Public Open House) and quantitative data 

(analysis findings included in the Phase 1 report, plus additional assessments completed as part of 

Task 3) demonstrating deficiencies and lack of suitable conditions from a transportation user 

perspective. 

Specific transportation improvement alternatives for OR 224 will be explored during this Task and may 

include, but are not limited to, parking configurations, wayfinding signage upgrades, pedestrian and 

wildlife crossing improvements, safety and operational improvements, context-sensitive design 

enhancements, bicycle facilities, etc. The final list of alternatives to be considered should include a 

range of options, from simple to complex, implementable by both the FS and ODOT, in coordination 

with other local entities. 
32

Task 5 – Final Corridor Master Plan Report

The OR 224 Corridor Master Plan Final Report will compile the data, analysis, findings and 

recommendations of the previous tasks into a comprehensive roadmap that will assist the USFS and 

ODOT in prioritizing future transportation improvements. The report will provide contextual background 

and summarize the process followed from stakeholder outreach, data collection, existing and future 

conditions documentation, needs identification, and alternatives development. The final OR 224 

Corridor Master Plan will include recommendations for implementing specific transportation solutions in 

response to the needs that were identified and the future vision that has been set forth by members of 

the local community. The final report will include an implementation plan that outlines the sequencing 

and phasing of capital and operational improvements and should address:

• Planning-level project cost estimates

• Prioritization of projects and initiatives

• Confirm funded and unfunded status

• Phasing of improvements

• Narrative text to clarify how actions will be advanced

Option for Planning and Environmental Linkages (PEL)

The OR 224 Phase 2 effort may benefit from a Planning and Environmental Linkages (PEL) study 

approach. FHWA defines PEL as a collaborative and integrated approach to transportation decisionmaking that considers benefits and impacts of proposed transportation system improvements to the 

environment, community, and economy during the transportation Planning Process. ODOT recently 

published a “Guide to Linking Planning and NEPA Using the ODOT PEL Questionnaire” in September 

2021 that provides information to planners and environmental staff on developing a PEL strategy. While 

this Phase 1 report outlines a high-level Phase 2 scope, the USFS, ODOT, and FHWA should consider

PEL as an option once funding has been secured and a detailed scope is needed.

Phase 2 Corridor Master Plan Cost Estimate

Table 7: OR 224 Phase 2 Corridor Master Plan Estimated Project Cost

Task Estimated Cost

1. Project Coordination, Communication and Management Plan and Kick-Off Meeting $50,000

2. Community Visioning, Goal Setting and Public Engagement $75,000

3. Finalize Existing Conditions Assessment and Define Desired Future Conditions $90,000

4. Needs Identification and Alternatives Development $200,000

5. Draft and Final Corridor Master Plan Report $75,000

Travel for Public Meetings and Site Visits $10,000

TOTAL $500,000
33

Appendix A

Safety and Traffic Assessment Technical Memorandum
Memorandum

Western Federal Lands Highway Division

610 E. Fifth Street

Vancouver, WA 98661

Date: September 10, 2021

From: Sean Kilmartin, P.E.

Highway Safety Engineer

To: Jamie Lemon, AICP 

Transportation Planner

Subject: OR 224 Corridor Study Phase 1 – Safety and Traffic Assessment

Introduction

As part of the Phase 1 Corridor Study along Oregon State Route 224 (OR 224) within the Mount 

Hood National Forest, the Western Federal Lands Highway Division (WFLHD) Highway Safety 

Team has conducted an analysis of the corridor from Mileposts 31.2 through 49.97 with respect 

to safety and operational concerns. The road is owned by the U.S. Forest Service (USFS) and 

maintained by the Oregon Department of Transportation (ODOT). This analysis follows a June 

16, 2021 site visit to the corridor.

Items reviewed and/or used for analysis as part of this assessment included:

• The ODOT TransGIS portal, which provides information on traffic data, lane widths, 

shoulder widths, mileposts (MP), signs, roadside barrier, and posted speed limits

• The ODOT Crash Data System, which provides location-specific crash history

• The Interactive Highway Safety Design Model (IHSDM), which is described below

• Aerial Imagery through a Bing Maps GIS layer

• Quadrangle maps through the United States Geologic Service (USGS)

• The Clackamas County Flood Insurance Study (FIS), which helped confirm the general 

grade of the river and the road (which generally follows the river throughout the 

corridor); the quad maps were the primary source of topographic data

• OpenRoads Designer, from which an approximated alignment was created to provide 

data for use by IHSDM

• The plan set for the OR DOT 224(1) Clackamas Highway Pavement Restoration Project 

(MP 31.73-MP 33.00 and MP 44.94-45.82)

• The ODOT Digital Video Log

This safety and traffic assessment has been mostly focused on baseline, pre-disaster conditions 

with some additional consideration given to future forest uses, users, and other considerations. 

Recommendations, where possible, are based on available information, but may sometimes 

require additional information or further study.
2

Traffic Data, Road Users, and Corridor Uses

The following average annual daily traffic (AADT) volumes, for both the current year and a 

potential design year (current year + 20 years) were retrieved from the ODOT TransGIS portal:

• MP 31.2-MP 39.1

o Current year: 560 vehicles per day

o Design year: 760 vehicles per day

• MP 39.1-MP 42.2

o Current year: 550 vehicles per day

o Design year: 760 vehicles per day

• MP 42.2-MP 48.3

o Current year: 480 vehicles per day

o Design year: 480 vehicles per day

• MP 48.3-MP 49.97

o Current year: 300 vehicles per day

o Design year: 320 vehicles per day

The percentage of the AADT that is truck traffic is 36.9% for all above segments, according to 

TransGIS. There is significant potential for seasonal traffic volumes to be significantly higher 

than the AADT volumes listed above. A potential goal for a future study would be to confirm 

traffic volumes within the corridor (including at some of the more prominent intersections and 

driveways). This confirmation may help planning or design efforts if there are ever future 

projects to add or upgrade parking, campground, or other forest features that would draw 

visitation and, potentially, congestion or user conflicts along with it. Posted speed limits are 55 

MPH.

OR 224 is now part of the West Cascades Scenic Bikeway. There are currently no counts

available for bicycle traffic, but the USFS did note that on a drive-through it is possible to see six 

to ten cyclists along the road. Bicycle traffic may also grow in the future if the corridor’s 

reputation as an enjoyable place to ride continues to grow. It is possible to gather bicycle counts 

once the corridor is reopened to the public; however, without previous baseline or pre-disaster 

bicycle counts, it will be more difficult to project bicycle traffic growth.

Pedestrians are an additional road user group to consider as part of the future corridor. Currently, 

there are no marked or signed pedestrian crossings within the study limits. However, the USFS 

noted that it is common for pedestrians to cross the road to access areas on the opposite side from 

where they park. Campgrounds, boating access areas, and other defined recreational features are 

the areas where these pedestrian crossings are most likely to occur, but with vehicles parking at a 

large number of places throughout the corridor, the potential for pedestrian crossings is 

increased. Additionally, there is concern that with the loss of vegetation that may have 

previously served as a barrier to access, pedestrian crossings may become even more hazardous 

in the future as access points have increased and are even less defined or obvious to drivers.
3

The USFS identified some of the primary ways in which those who access this area of Mount 

Hood National Forest use this corridor:

• Scenic driving, including motorcycle or bicycle traffic

• Camping, including on and off designated campgrounds

• Hiking, picnicking, mushroom picking, target shooting, and other ‘on foot’ activities

• River activities, including boating and kayaking, as well as winter sports and activities

• Commercial activities, including maintenance of the hydroelectric facilities, other 

utilities, or logging activities (including through traffic)

The above list is not all-inclusive, and the complete list of needs for each of those uses is outside 

of the scope of a safety and traffic assessment. However, these needs must be considered when 

intersecting with corridor safety needs, parking needs, and other traffic needs. Currently, there 

are a large number of vehicles parking at undesirable locations throughout the entire corridor, 

creating safety and environmental concerns. The parking in undesirable areas is expected to be 

exacerbated following the loss of vegetation. Visitors who park in these undesirable areas may 

also be participating in other activities, such as target shooting or camping, in undesirable or 

unsafe areas. Another consideration is the different goals of the road users. Some of those 

visiting the corridor for scenic driving or other recreational activities may at times be driving at 

lower speeds. Those using the corridor for commercial activities may be incentivized to travel at 

higher speeds. These speed differentials, while difficult to model when caused by recreation, can 

increase the risk of crashes.

Existing Guardrail and Roadside Condition

Extensive guardrail damage was observed throughout the corridor. An accounting of the 

following will be needed:

1. Guardrail damaged by during the disaster or during disaster-recovery that will be 

replaced in-kind once the post-disaster logging activities are complete.

2. Guardrail (specifically guardrail that does not meet current crash testing criteria) that was 

not damaged and will not be replaced in kind.

3. Locations where there is no existing guardrail but, with post-disaster conditions, may be 

warranted as part of a potential future project.

An inventory of all existing guardrail in the corridor (from ODOT TransGIS, see above link) is 

included in Appendix E. Given the high risk of slides or fallen trees throughout the corridor, it is 

assumed that continued monitoring of the roadside is needed as more guardrail may become 

damaged until the area stabilizes. The area may not fully restabilize until the downslopes become 

revegetated.

The starting point for evaluating where new guardrail may be needed is an evaluation of the clear 

zone throughout the corridor. According to Section 3.1 of the AASHTO Roadside Design Guide, 

the clear zone is the unobstructed, traversable area provided beyond the edge of the traveled way 

for the recovery of errant vehicles. The shoulder, any turnouts, and any roadside area free of 
4

obstructions with slopes 1V:4H or flatter are considered to be part of the clear zone. Descriptions 

of recoverable, traversable, and non-traversable and non-recoverable slopes are as follows:

• Slopes 1V:4H are considered to be traversable and recoverable, meaning that an errant 

vehicle that reaches this type of slope can generally stop their vehicle or slow them 

enough to return to the roadway (if the slope is wide enough and free of obstructions).

• Slopes steeper than 1V:4H but flatter than 1V:3H are considered to be traversable but 

non-recoverable. Errant vehicles that encounter slopes in this range cannot likely navigate 

back to the roadway or come to a complete stop, but can likely be expected to reach the 

bottom of the slope without rolling over. Slopes in this range are if there are no 

obstructions on the slope or at the toe of the slope, and if there are slopes 1V:4H or flatter 

at the toe, then the clear zone resumes at the toe of the slope where vehicles have the 

opportunity to safely come to a stop.

• Slopes steeper than 1V:3H are considered to be non-traversable and non-recoverable, 

meaning that vehicles that encounter slopes in this range cannot recover to the roadway 

and cannot safely steer to the bottom. Slopes in this range present a rollover risk that 

increases proportionately to slope steepness (especially for slopes steeper than 1V:2H). 

No field measurements were taken on the June 16, 2021 site visit, but based on 

observations and the contour lines from the USGS quad maps, it seems that most slopes 

in the corridor fall into this range. With the loss of vegetation, many roadside slopes 

appeared to be undergoing soil erosion, causing the slopes to steepen in areas where the 

soil has migrated down-slope.

The AASHTO Guidelines for the Geometric Design for Low Volume Roads may apply to this 

corridor when determining the recommended clear zone width since the average daily traffic is 

less than 2000 vehicles per day, according to the ODOT Trans GIS site. However, until there is 

confirmation of seasonal highs in traffic volumes, it may be more appropriate to refer to Table 3-

1 of the AASHTO Roadside Design Guide for recommended clear zone widths:

• Foreslopes (downhill):

o 1V:6H or flatter – 12 to 14 feet

o 1V:5H to 1V:4H – 14 to 18 feet

• Backslopes (uphill):

o 1V:3H – 8 to 10 feet

o 1V:5H to 1V:4H – 10 to 12 feet

o 1V:6H or flatter – 10 to 12 feet

IHSDM Description

The Interactive Highway Safety Design Model (IHSDM) is a suite of software analysis tools for 

evaluating safety and operational effects of geometric design in the highway project development 

process. The IHSDM contains six modules that can be used to evaluate nominal and substantive 

safety performance. For this study, WFLHD Safety used the Crash Prediction, Policy Review, 

Design Consistency, and Traffic Analysis Modules to evaluate the OR 224 corridor. 
5

With no available survey, a variety of sources were used to acquire or approximate the data 

needed to run IHSDM. A horizontal alignment was approximated in OpenRoads Designer with 

the use of aerial imagery. A vertical alignment was approximated with the use of USGS quad 

maps, and a drive-through of the corridor on the June 16, 2021 site visit confirmed no significant 

grades or grade changes that would have a major effect on IHSDM output. Data for lane widths, 

shoulder widths, and guardrail locations were taken from the ODOT TransGIS site. Cross slope 

data was approximated to be 2% for a typical tangent section. For curve sections, the cross slopes 

were approximated to the appropriate superelevation for each radius as listed in the AASHTO 

Policy on Geometric Design of Highways and Streets (8% maximum table, Table 3-10). Inputs 

for the roadside data were based on the USGS quad maps, Google Streetview imagery, and aerial 

imagery. Traffic and crash data were as listed previously in this memorandum.

Some key assumptions and further description of the use of IHSDM and these four modules for 

this analysis are listed in Appendix A. Please refer to this section to further understand the 

context of the model for this analysis.

IHSDM Output Data Analysis

The IHDSM software divides the roadway into segments based on changes in roadway 

geometry, such as lane width, shoulder width, cross slope, or roadside hazard rating, as well as 

changes in traffic data or behavior. 206 segments were identified within this corridor. To ease the 

analysis of the output data, the segments were combined into 12 distinct groups based on similar 

features such as tangent sections, reverse curves, or similar roadside conditions. A description of 

the 12 groups is as follows (see Appendix B for more information):

TABLE 1: OR 224 Groups

Group 

Number

Start 

MP*

End 

MP* Description

1 31.2 32.6 Long, high radius curves; adjacent to significant recreational facility

2 32.6 34.5 Series of lower radius, shorter curves

3 34.5 35.6 Fairly straight section

4 35.6 37.8 Series of curves, including a change in horizontal alignment of approx. 180°

5 37.8 39.2 Fairly straight section

6 39.2 41.0 Series of curves, mix of medium and high radius

7 41.0 42.3 Fairly straight section

8 42.3 44.2 Series of curves, higher radius as compared to Group 8

9 44.2 46.4 Series of curves, including changes in horizontal alignment of approx. 90° 

10 46.4 47.5 Fairly straight section

11 47.5 49.0 Winding section with curves of varying lengths, some lower radius

12 49.0 49.97 End of corridor, more driveways, lower speed limit

*Mileposts listed are approximate
6

The Design Consistency and Traffic Analysis Modules were used to help examine expected 

speeds throughout the corridor. IHSDM runs a speed model through the geometry, taking into 

account horizontal curves and vertical grades in order to determine the effects that geometry has 

on speed (e.g. faster on steeper downgrades, slower on steeper upgrades). The results are 

sensitive to the Desired Speed input, which is estimated here in absence of formal speed data. 

For a design speed such as 55 mph, proposed for use on this project, an estimate of 65 mph was 

used since the corridor is characterized by long tangent sections with minimal significant grade 

changes. Anecdotally, as noted by the USFS at the June 16, 2021 site visit, risky driving (and, at 

times, impaired driving) is commonplace enough during the high visitation season to be a 

significant concern. The speed model helps the project team with locating higher discrepancies 

between expected speed and design speed of individual geometric elements such as horizontal 

and vertical curves. This can help fine-tune countermeasures such as warning signage to better 

align with motorist’s expectations. 

Data gained through the Crash Prediction Module, the Policy Review Module, and the Design 

Consistency Module were used to compare groups (due to approximated data, the Driver/Vehicle 

Module failed to run and data from the Driver/Vehicle Module was not included in the results 

analysis). The comparison was completed with the following data:

1. Expected Crashes data adjusted by group length (crashes/group/mile). This data relies on 

an Empirical-Bayes analysis using historical crash data. This data is noted as ‘Expected 

Crashes’ for the remainder of the report.

2. Predicted Crashes data adjusted by group length (crashes/group/mile). This is the default 

model for crash prediction within IHSDM and relies on roadway geometry, roadside 

features and other program inputs. This data is noted as ‘Predicted Crashes’ for the 

remainder of the report. The predicted crash data is especially important for this analysis 

due to the age of the historical crash data.

3. Total expected crashes per group.

4. Total predicted crashes per group.

5. Design Consistency Module flagged data within each group (i.e. segment with an element 

not designed according to the AASTHO Green Book counted as one flag).

6. Policy Review Module flagged data within each group (i.e. each severe speed differential 

or deficient stopping sight distance within each segment counted as one flag).

These six items for each group were compared to their position with respect to the 90th percentile 

number and the 75th percentile number for each data set. For example, a group with predicted 

crashes based on Empirical-Bayes data in the 90th percentile as compared to all other groups 

received 1 point. A group with predicted crashes based on Empirical-Bayes data between the 75th

percentile and the 90th percentile as compared to all other groups received 0.5 points. Groups 

with Empirical-Bayes crashes data below the 75th percentile received 0 points. Scores were 

totaled for the 12 groups and then ranked. Several groups were identified for further analysis. 

The IHSDM analysis and results allows for data-driven safety analysis to identify the sections of 

the project that would benefit the most from specific safety features, discussed in the Data 

Analysis section. 
7

Existing Data Analysis

The 12 groups are identified and described within Appendix B. These groups were scored based 

on criteria numbers 1-6 identified in the above IHSDM Output Data Analysis section. The

ranked by risk groups are shown in Table 2 below (see Appendix C for more information on the 

data and scoring):

Table 2: Ranked by Risk OR 224 Groups

Rank Group Start MP End MP

1 4 35.6 37.8

2 11 47.5 49.0

3 2 32.6 34.5

4 9 44.2 46.4

5 8 42.3 44.2

6 10 46.4 47.5

7 1 31.2 32.6

8 3 34.5 35.6

8 5 37.8 39.2

8 6 39.2 41.0

8 7 41.0 42.3

8 12 49.0 49.97

The Crash Prediction Module results for the corridor are in part summarized through the 

following tables:

Table 3: Comparing Crash Prediction Module Expected and Predicted Crashes (Existing

Conditions – 20-Year Design Life)

Crash Prediction 

Module Method

Total 

Crashes

Fatal & Injury 

Crashes

Percent Fatal 

& Injury

Property Damage 

Only Crashes

Percent Property 

Damage Only

Predicted 108.24 34.74 32.10% 73.50 67.90%

Expected 137.12 70.84 51.67% 66.27 48.33%

Percent Difference 21.06% 50.95% 10.90%

Table 3 shows the breakdown of expected crashes by those resulting in Fatal and Injury (FI) and 

those resulting in Property Damage Only (PDO). As shown, between 32% and 52% of all 

crashes result in a fatality or an injury, indicating the risk of roadway departures in this corridor. 

A roadway departure crash occurs when there is a crash that involves a vehicle crossing 

centerline, an edge line, or a lane line.
8

The expected crash data, which relies on historical crash data, shows an elevated percentage of 

fatal and injury crashes. This is a strong indication that the risk of severe crashes in the corridor 

is higher than what could be anticipated when reviewing the roadway and roadside strictly by its 

geometry and features. Driver behavior may be one explanation. Expected and predicted crash 

data cover a 20-year design life and account for the projected increase in traffic volume 

(exposure) over time.

Table 4: Expected Crash Type Distribution (Existing Conditions – 20-Year Design Life)

Crash Type

Fatal and Injury Property Damage 

Only Total

Crashes Crashes 

(%) Crashes Crashes (%) Crashes Crashes (%)

Collision with Animal 2.69 2.00% 12.19 8.90% 16.59 12.10%

Collision with Bicycle 0.28 0.20% 0.07 0.00% 0.27 0.20%

Other Single-vehicle Collision 0.5 0.40% 1.92 1.40% 2.88 2.10%

Overturned 2.62 1.90% 0.99 0.70% 3.43 2.50%

Collision with Pedestrian 0.5 0.40% 0.07 0.00% 0.41 0.30%

Run Off Road 38.61 28.20% 33.47 24.40% 71.44 52.10%

Total Single Vehicle Crashes 45.20 33.00% 48.71 35.50% 95.02 69.30%

Right-Angle Collision 7.16 5.20% 4.77 3.50% 11.65 8.50%

Head-on Collision 2.41 1.80% 0.2 0.10% 2.19 1.60%

Other Multi-vehicle Collision 1.84 1.30% 1.99 1.40% 3.70 2.70%

Rear-end Collision 11.69 8.50% 8.09 5.90% 19.47 14.20%

Sideswipe 2.69 2.00% 2.52 1.80% 5.07 3.70%

Total Multiple Vehicle Crashes 25.79 18.80% 17.56 12.80% 42.09 30.70%

Total Expected Crashes 70.98 51.80% 66.27 48.30% 137.12 100.00%

Table 4 shows the expected crash type distribution. Single-vehicle crashes are highlighted in 

green. Multi-vehicle crashes are highlighted in yellow. Corridor totals are highlighted in orange. 

As shown, the largest number of crashes were single vehicle roadway departures. These three 

tables, in addition to all other IHDSM output especially those specific to the more at-risk groups, 

help to identify effective and cost-efficient crash reduction features that can be applied to the OR 

224 corridor. 

Discussion of Recommendations and Potential Next Steps for Bicycle 

Facilities

A project to widen the roadway to accommodate 4- to 5-foot shoulders throughout the entire 

corridor would require a significant amount of earthwork, disturbance to environmentallysensitive areas, potential bridge widening, and cost. While widening may be the ideal solution to 
9

cyclist accommodation, the below discussion is based on the roadway template remaining the 

same in the future.

There is readily available online marketing and information for the West Cascades Scenic 

Bikeway, but signs and pavement markings for cyclists are limited south of Estacada. At a 

minimum, select placement of W11-1 Bicycle with supplementary W16-1P Share the Road 

plaques will help reinforce the presence of bicycles on the road or shoulder. 

An additional option would be the use of dynamic warning signs (with either flashing LEDs or 

beacons) that become activated when bicycles are located within certain areas. These work by 

registering bicycle traffic counts and activating the flashing devices for a certain amount of time 

until cyclists have cleared an area. These are useful for areas where the shoulder is minimal and 

cyclists are within the roadway, and are especially useful for when cyclists can be expected 

within the roadway and there is limited sight distance. Potential locations along OR 224 for these 

types of devices would be in advance of select bridges (depending on shoulder width), areas 

where the road face extends adjacent to the inside of curves and limits sight distance, areas 

where there may be significant roadside parking and cyclists are pushed into traveling in the 

road, or to cover general areas where bicycle traffic volumes are anticipated to be high. These 

types of devices (with flashing beacons rather than LED lighting) are used elsewhere in Oregon, 

such as along OR 26, Cascade Lakes National Scenic Bikeway, and OR 242 near McKenzie Pass 

(see Figure 1 below):

Figure 1: Dynamic Warning Signage for Bicycles (OR 242, MP 78.6, ODOT Digital Video Log)
10

One definite recommendation would be the use of wider edge lines throughout the corridor 

(compared to the current 4-inch wide lines). These lines provide improved delineation between 

the lane and shoulder, which may help to better separate motorists from cyclists. They also 

provide an 18% reduction in crashes of all types and severities. When WFLHD recommends 

wider edge lines, it typically recommends 6-inch wide lines. The ODOT Pavement Marking 

Standard Detail Blocks (TM500) show only 4-inch and 8-inch wide lines; if wider edge lines are 

used, coordination with ODOT would be necessary to determine the appropriate width for this 

road.

Discussion of Recommendations and Potential Next Steps for Parking, 

Pedestrians, and Adjustments to Vegetation Screen Loss

Any improvements installed within the corridor to improve parking (either additions or 

discouragements), to improve pedestrian facilities, and to accommodate for the loss of a 

vegetation screen along the roadway will likely need to be complementary in order to provide the 

highest benefit. While there will be parking along the road throughout the corridor, the areas 

with the highest concentration of parking will be the areas in which there is some type of 

attraction that will draw overnight visitation. The vegetation screen loss causes the highest 

concern in the areas where there are campgrounds, spot camping, or environmentally-sensitive 

features that could be damaged by vehicles parking off-pavement. The areas with the highest 

number of parked vehicles will correlate directly with the highest number of pedestrians and, 

depending on the attraction, may correlate with the highest number of pedestrian crossings.

Other US National Forests, as well as other federal agencies, are struggling with roadside 

parking in undesirable areas. A presentation provided to Yellowstone National Park, detailing the 

known methods of discouraging parking in undesirable areas, is included in Appendix F. These

methods have all had mixed results, though no formal study has ever been completed on any 

areas in which these methods have been implemented. Based on the different uses of the OR 224 

corridor, there will not likely be a ‘one size fits all’ solution. One example of an area where 

solutions to restrict parking and/or access may be needed is near MP 41.0. Visitors either park on 

one side of the road to cross to the opposite (east) side or drive their vehicles into traversable 

areas on the east side that are not defined as access driveways. In addition to the earth 

disturbance, these visitors use the hillside on the east side for target shooting. There is a parking 

area on the west side which has space for picnicking or access to the river. The target shooting is 

in range of this parking area as well as the road. While target shooting is a draw to the forest, this 

is not the most appropriate area for it and methods of further discouraging use in this particular 

area are of interest.
11

Figure 2: Area of Concern for Parking and Access (OR 224, MP 41.0)

One method of parking discouragement discussed at the June 16, 2021 site visit is guardrail 

installation. Guardrail is only recommended in areas where the crash as a result of a roadside 

departure is more severe than a crash caused by a vehicle striking the guardrail itself. Specific to 

areas of campgrounds or spot camping, a consideration for guardrail installation would be the 

clear zone width and location of the campers. Further discussion of guardrail and roadside 

design, including the clear zone, is included in the next section. The next steps include a review 

of the roadside slopes, a delineation of areas where parking should be discouraged, the location 

of the campgrounds compared to the clear zone width, and an analysis of the roadside condition.

Pedestrian facilities should be coordinated with both the future usage of campgrounds and the 

future context of any existing or proposed recreational facilities. Pedestrian crossings should be 

provided in any areas where parking is provided and there is some type of attraction on the 

opposite side of the road. Methods of funneling pedestrians to a defined crossing will be sitespecific. The type of crossing will depend on both the number of anticipated pedestrian crossings 

and the stopping sight distance along the highway. Features that could be included in a 

pedestrian crossing may include crosswalk markings, advanced warning signage, in-street 

signage, or rectangular rapid flashing beacons. The next steps include a review of roadside 

attractions, a review of any existing and any planned or proposed recreational facilities, and an 

estimation of potential pedestrian crossings based on those attractions or facilities. High visibility 

crosswalk markings have a 48% crash reduction factor for potential crashes involving 

pedestrians (which have a high probability of resulting in a fatality). Advanced Stop/Yield for 

Pedestrians signs and markings have a crash reduction factor of 25%. Rapid flashing beacons 

installed at crossings have a crash reduction factor of 47% for crashes involving pedestrians. 
12

There is benefit to using more than one of these treatments at a location; for example, high 

visibility markings used with advanced signs and markings will reduce the probability of crashes 

involving pedestrians by more than 48%. Crash reduction factors cited in this report are based on 

data or reports identified in the Crash Modification Factor Clearinghouse or the AASHTO 

Highway Safety Manual. A crash reduction factor is applicable when an installed feature can 

reduce the risk (either in probability or in severity) of future crashes. Lighting and raised 

crosswalks may also be options.

Figure 3: High Visibility Crosswalk Markings with In-Street Signage (Yellowstone National 

Park; installation along OR 224 likely not in stop-controlled areas)

Discussion of Recommendations and Potential Next Steps for Guardrail 

and Roadside Design

The final inventory of guardrail replaced as a result of the disaster will help guide any further 

efforts on guardrail; the preliminary accounting of anticipated guardrail replacements will have 

to be compared to the actual replacements following the logging and utility work. Once it is 

determined how much of the existing guardrail has been replaced, the next step is to determine 

how much of the remaining guardrail must be replaced to meet current crash testing criteria. 

Additionally, a review of the existing bridge rail throughout the corridor is needed.

The final step relating to guardrail is to determine how much additional guardrail is needed, 

based on new conditions following the fire. New guardrail installation will likely have to be 

balanced between relative roadside departure risk and cost. To determine where new guardrail 

may be warranted, a full evaluation of the clear zone in locations where there is no existing 
13

guardrail is recommended. A special focus on the areas where there has been significant 

vegetation loss may be needed. Once the clear zone and roadside slopes and actual clear zone 

widths are documented (compared to recommended), guardrail warrants can be developed. 

However, it is likely that there will be budgetary restrictions on new guardrail installation. Rather 

than simply developing a list of locations where new guardrail is warranted, it is recommended 

to develop a priority list for where guardrail and other roadside design treatments are most 

beneficial. 

Figure 4: Apparently Undamaged Guardrail and Bridge Rail (OR 224, MP 31.2)
14

Figure 5: Apparently Undamaged Guardrail and Bridge Rail (OR 224, MP 49.97)

In other WFLHD-designed roadway projects where there are similar budgetary restrictions on 

guardrail installation or other considerations (i.e. environmental or wildlife impacts, aesthetics, 

etc.), WFLHD Safety has used a benefit/cost procedure to determine where guardrail could 

provide the highest value. Two programs available for completing this type of analysis are the 

AASHTO ROADSIDE procedure (outlines in previous additions of the Roadside Design Guide 

and used by the Alaska DOT&PF) and the Roadside Safety Analysis Program (RSAP). WFLHD 

Safety has used the ROADSIDE procedure previously. The benefits identified in these 

procedures are the reduction in crashes or the reduction in crash severities over the 20-year 

design life; the costs to which the benefits are compared are the initial construction costs of 

installation and the maintenance costs of repairs over the 20-year design life. Through the 

FHWA Highway Safety Improvement Program (HSIP), each state has placed a tangible, 

economic cost to different crash types; some of these costs include medical costs, property 

damage, emergency services, productivity losses, congestion impacts, insurance costs, and other 

legal claims. The opportunity to reduce these economic costs, or human impact costs, is 

considered to be a benefit. The actual costs used in these types of analysis are construction and 

maintenance costs, including potentially embankment material, guardrail, guardrail terminal 

sections, or vegetation clearing. Additionally, this analysis can identify other options that may be 

more cost effective than guardrail, such as providing full or partial clear zone treatments (i.e. find 

the optimized foreslope combinations and widths). 
15

Discussion of Recommendations and Potential Next Steps for Other 

Safety Countermeasures

The IHSDM results can help guide the placement of safety countermeasures including signage, 

rumble strips, and delineators. From the site visit on June 16, 2021, it appeared that much of the 

signage throughout the corridor was in the appropriate location. Centerline rumble strips were 

present throughout much of the corridor, though were somewhat worn down. Delineators may 

have been common in the areas where there is existing guardrail (though it was difficult to 

determine due to the damage to the guardrail), but appeared to be less common in areas where 

there is no existing guardrail.

The next step, once a decision on previously discussed recommendations has been made, would 

be to use the IHSDM results to determine if any additional safety countermeasures are 

recommended. Examples would include:

• Additional curve warning signage. Depending on the type of signage, a crash reduction 

factor of 25-40% is applicable for signed curves, showing a high value in areas where 

there is a significant crash history or where IHSDM has shown elevated risk.

• Additional delineators (especially in areas where guardrail has been shown not to be costeffective or where there are not sufficient funds to install guardrail). A crash reduction 

factor of 11% is applicable for delineators placed on horizontal curves; there is additional 

benefit, though not yet quantified, for delineators placed on tangent sections with steep 

drop-offs.

• High friction surface treatment (especially in areas where the curve radius or 

superelevation is deficient compared to the recommended values in the AASHTO Green 

Book). A crash reduction factor of 24% is applicable through the length of curves where 

high friction surface treatment is installed, and this treatment may have a higher 

benefit/cost ratio than superelevation correction or curve flattening. The benefit is even 

higher with respect to reducing crashes in wet weather.

• Wider edge lines (discussed in the bicycle section, but the highway safety benefits are 

present regardless of impacts on bicycle traffic). Wider edge lines have a crash reduction 

factor of 18%.

• Long-term: review crashworthiness of bridge rail throughout the corridor.

Historic crash data was reviewed and used to the extent necessary to run IHSDM, but a more 

thorough look at individual crashes and trends is needed. For the purpose of this study, the data 

was gathered and included in Appendix D (no personally identifiable information included). It is 

recommended that any future study or project complete the review of the latest crash data. A 

summary by severity of the crashes along OR 224 between 2010 and 2019 is as follows:

• 7 crashes in which the most severe outcome was a fatality (K)

• 8 crashes in which the most severe outcome was a serious injury (A)

• 37 crashes in which the most severe outcome was a moderate injury (B)

• 27 crashes in which the most severe outcome was a minor injury (C)

• 16 crashes in which the most severe outcome was property damage only (PDO)
16

According to the ODOT 2019 State Highway Crash Rate Tables, the crash rate for non-freeway 

type roads is 1.40 crashes per million vehicle miles traveled. Assuming 560 vehicles per day in 

the corridor over 18.8 miles, the crash rate in this corridor may be as high as 2.47 crashes per 

day. Given that traffic decreases over the length of the corridor, this may be on the low end of 

the crash rate.

A final consideration is emergency management. At the kickoff meeting, a desire was indicated 

to investigate dynamic signage to convey messaging to the public. This messaging could include 

road closures due to slides, wildfires, or other events. It could also indicate evacuation route 

information or other critical information. The type and placement of this signage will have to be 

coordinated with both the USFS and ODOT. It will have to be determined which agency would 

control the messaging, and how they will do so. A source of power would also have to be 

identified.

Summary of Recommendations

Bicycle Facilities

I. When visitation has normalized, conduct traffic counts to better understand seasonal 

traffic data (including bicycles), especially to understand the post-disaster differences in 

use throughout the corridor from the pre-disaster conditions. Many of the 

recommendations will be dependent on this data. The Forest should also coordinate with 

ODOT and WFLHD to identify traffic count needs to the south of the ODOT-maintained 

highway.

II. Determine appropriate locations for additions of W11-1 Bicycle with supplementary 

W16-1P Share the Road plaques.

III. Determine feasibility of dynamic warning signs (with either flashing LEDs or beacons) 

that become activated when bicycles are located within certain areas.

IV. Determine feasibility of wider edge lane markings (requires coordination with ODOT).

V. Long-term: determine if shoulder widening is feasible or desired to provide 4- to 5-foot 

shoulders throughout the entire corridor.

Parking, Pedestrians, and Vegetation Screen Loss

A. Determine locations where parking is undesirable and determine (from Appendix G, or 

from any other found sources) potential treatments to help discourage parking in those 

areas.

B. Determine, in coordination with any potential planned recreational facility additions or 

upgrades and with consideration of any attractions or overnight visitation areas, where 

pedestrian crossings are most likely. Based on the availability of parking or the popularity 

of the attractions or overnight visitation areas, estimate the number of daily pedestrian 

crossings. 

C. Based on B above, determine the appropriate treatments at planned pedestrian crossings. 

Options include crosswalk markings, advance signage and markings, and rapid flashing 

beacons. If there is to be a major crossing, lighting may also be considered, but it is 
17

probable that such a major crossing does not exist in this corridor. Raised crosswalks are 

another option, though the impacts on maintenance and traffic must be considered.

Guardrail and Roadside Design

i) Review the final inventory of replaced guardrail. 

ii) Determine the amount of remaining existing guardrail (including terminal sections) that 

must be upgraded in order to meeting current crash testing criteria.

iii) Determine the actual clear zone throughout the corridor.

iv) Determine a priority list of placement of new guardrail. A benefit to cost procedure, 

discussed previously in this report, is likely necessary in order to determine the locations 

of highest value of new guardrail placement.

v) Where guardrail may be warranted but cannot be installed due to lack of funding or other 

considerations, review other safety countermeasures (below) for alternatives.

Other Safety Countermeasures

1) Once a determination has been made on recommendations for bicycles, parking, 

pedestrians, vegetation screen loss accommodations, guardrail, and roadside design, 

consider any remaining safety countermeasures that may be needed either to account for 

other risks or to account for any recommendations that could not be implemented due to 

cost or other considerations.

1.1. This includes but is not limited to curve warning signage, delineators, and high 

friction surface treatment.

2) Complete review of historic crash data (see Appendix D).

3) Determine feasibility of installation of dynamic signage for emergency management. The 

type, location, and control will have to be coordinated between USFS and ODOT.

Strategies for Improving Data Collection, Analysis and Implementation of Safety Features

FLH Safety is currently conducting a GIS and systemic safety research project in order to 

provide FLH partner agencies with better tools to supplement a lack of traffic and safety data as 

well as efficiently analyze road networks for safety improvements. The pilot GIS tool is 

available for use and can be customized for the overall studies in the entire corridor (i.e. from 

Estacada to Detroit). For example, the locations of historical and current high-use and/or 

undesirable parking areas and pedestrian activity can be captured within the GIS application. 

These efforts, along with other Forest efforts, could be combined to help build a robust set of 

data while the next funding phase is identified and programmed. Contact WFLHD Safety and 

Planning for more information. 

Other funding programs should be investigated further to identify which could be utilized to 

implement future improvements. These could include the ODOT-administered Highway Safety 

Improvement Program, the High-Risk Rural Roads program and the All Roads Transportation 

Safety program. These programs could help leverage FLAP, FLTP and other funding sources 

that ODOT and the Forest typically utilize in order to provide additional safety funding. 
18

Performing the analysis and further study as discussed in this memorandum puts ODOT and the 

Forest well on the way to completing a Local Road Safety Plan, a FHWA initiative to bring 

transportation users home safely. The agencies and stakeholders in this corridor should consider 

partnering together to create a plan and strengthen ties among engineering, enforcement, 

education and emergency services countermeasures to reduce fatal and serious injury crashes. 

If there are any questions on the content of this memorandum, please contact Sean Kilmartin at 

360-619-7686 or sean.kilmartin@dot.gov.
Safety and Traffic Appendix A 

IHSDM Discussion 

 
IHSDM Discussion Reference:

https://cms7.fhwa.dot.gov/research/interactive‐highway‐safety‐design‐model/modules/modules

Crash Prediction Module 

The IHSDM Crash Prediction Module estimates the frequency of crashes on a highway using 

geometry design and traffic characteristics. It is an implementation of the crash prediction 

methods documented in part C of the American Association of State Highway and 

Transportation Officials’ (AASHTO) First Edition Highway Safety Manual (HSM)—includes 

capabilities to evaluate rural two-lane highways, rural multilane highways, urban/suburban 

arterials, freeway segments, and freeway ramps/interchanges (including ramps, collectordistributor (C-D) roads, and ramp terminals). The algorithms for estimating crash frequency 

combine statistical Safety Performance Functions (SPFs)—i.e., base models—and crash 

modification factors (CMFs). SPFs are available for roadway segments, many types of 

intersections, freeway ramps, C-D roads, and ramp terminals. The Crash Prediction Module was 

run for this project for the years of 2021 through 2041. Site-specific historical crash data was 

available for this analysis, but was not as current as desired. 2% normal cross slopes for the 

length of each alignment alternative were used. Superelevation data was estimated based on the 

AASHTO Greenbook as an assumption, but will need to be confirmed as part of the design 

process. Recommendations may need to be altered where superelevation design criteria cannot 

be met. Roadway widths were assumed to be 24 feet (12 feet, 0 inch lanes) with four-foot 

shoulders on both sides of the road (with some narrowed sections). Existing guardrail locations 

and are known and were used for this analysis, but will need to be reviewed through further 

phases of a study. 

Design Consistency Module 

The IHSDM Design Consistency Module helps diagnose safety concerns at horizontal curves. 

Crashes on two-lane rural highways are over-represented at horizontal curves, and speed 

inconsistencies are a common contributing factor to crashes on curves. This module provides 

estimates of the magnitude of potential speed inconsistencies. The DCM uses a speed-profile 

model that estimates 85th percentile, free-flow, passenger vehicle speeds at each point along a 

roadway. The speed-profile model combines estimated 85th percentile speeds on curves 

(horizontal, vertical, and horizontal-vertical combinations), desired speeds on long tangents, 

acceleration and deceleration rates exiting and entering curves, and an algorithm for estimating 

speeds on vertical grades. Speeds entering or exiting the corridor at the northern and southern 

ends of the project were estimated to be 55 MPH at either end. 

Policy Review Module 

The Policy Review Module checks roadway-segment design elements for compliance with 

relevant highway geometric design policies. The module provides electronic files replicating 

quantitative policy values specified by the American Association of State Highway and 

Transportation Officials (AASHTO) in the 1990, 1994, 2001, 2004, and 2011 editions of “A 

Policy on Geometric Design of Highways and Streets” and automates checks of design values 

against those policy values. The Interactive Highway Safety Design Model (IHSDM) also 

provides a tool for inputting policy tables from other agencies’ design policies. The module, 
IHSDM Discussion Reference:

https://cms7.fhwa.dot.gov/research/interactive‐highway‐safety‐design‐model/modules/modules

which is applicable to rural two-lane and rural multilane highways, organizes checks into four 

categories: cross section, horizontal alignment, vertical alignment, and sight distance. Crosssection checks include through-traveled way width, auxiliary lane width, shoulder width and 

type, cross slope rollover on curves, bridge width, bike lane width, and (on rural multilane 

highways only) median width. Horizontal alignment checks include radius of curvature, 

superelevation rate, length of horizontal curve, and compound curve ratio. Vertical alignment 

checks include tangent grade and vertical curve length. The Policy Review Module can also 

check stopping, passing (on rural two-lane highways), and decision sight distance. 

Traffic Analysis Module 

The Traffic Analysis Module uses the TWOPAS traffic simulation model to estimate traffic 

quality-of-service measures for an existing or proposed design under current or projected future 

traffic flows. The traffic analysis module facilitates use of TWOPAS by feeding it the roadway 

geometry data stored by IHSDM. TWOPAS is the microscopic traffic simulation model that was 

previously used to develop the two-lane highway chapter of the Transportation Research Board’s 

(TRB) “Highway Capacity Manual.” TWOPAS produces measures including average speed and 

percentage of time spent following other vehicles. TWOPAS has the capability to simulate any 

combination of grades, curves, sight restrictions, no passing zones, and passing and climbing 

lanes. It is particularly useful for understanding variable traffic speeds throughout the corridor. 

‘Steep Grade’ was selected to describe the alignment for both increasing and decreasing stations. 

The vehicle flow rate used was the Design Hourly Volume (Design Year ADT*0.15 – K Value 

selected for rural roadway). 

Driver/Vehicle Module 

The objective of the Driver/Vehicle Module is to permit the user to evaluate how a driver would 

operate a vehicle (e.g., passenger car or tractor-trailer) within the context of a roadway design 

and to identify whether conditions exist in a given design that could result in loss of vehicle 

control (e.g., skidding or rollover). The Driver/Vehicle Module consists of a Driver Performance 

Model linked to a Vehicle Dynamics Model. Driver performance is influenced by cues from the 

roadway/vehicle system (i.e., drivers modify their behavior based on feedback from the vehicle 

and the roadway). Vehicle performance is, in turn, affected by driver behavior/performance. The 

Driver Performance Model estimates a driver's speed and path along a two-lane rural highway in 

the absence of other traffic. The resulting estimates serve as input to the Vehicle Dynamics 

Model, which estimates measures including lateral acceleration, friction demand, and rolling 

moment. The driver type selected was ‘Nominal’. The path decision selected was ‘Center’. The 

vehicle type selected was ‘Passenger Car’ (the module could not be completed for any alignment 

alternatives when using ‘Truck’). The road familiarity selected was ‘Curve Segment’. 
Safety and Traffic Appendix B 

IHSDM Group Map and Group Locations 

 




Group 3: MP 34.5 ‐ MP 35.6









Safety and Traffic Appendix C 

IHSDM Output Data Summary and Scoring for 

Existing Conditions 

 
90th Percentile 90th Percentile 90th Percentile 90th Percentile 90th Percentile 90th P

12.42 19.94 6.90 10.28 6.00 

75th Percentile 75th Percentile 75th Percentile 75th Percentile 75th Percentile 75th P

11.64 14.34 6.25 7.63 5.25 

Group Start MP End MP

Predicted Crashes by

Group Evaluation

Period

Expected Crashes by

Group Evaluation Period

Predicted Crash Rate by

Group Evaluation Period

(Crash/mi)

Expected Crash Rate by

Group Evaluation Period

(Crash/mi)

Design

Consistency Flags

by Group

Polic

Flags 

1 31.2 32.6 9.19 10.15 6.27 6.93 3 

2 32.6 34.5 11.40 20.32 6.24 11.11 6 

3 34.5 35.6 5.16 7.27 4.71 6.63 1 

4 35.6 37.8 15.29 20.05 6.97 9.14 3 

5 37.8 39.2 6.27 9.34 4.78 7.12 1 

6 39.2 41.0 10.54 10.97 5.83 6.07 5 

7 41.0 42.3 6.78 6.01 5.14 4.56 2 8 42.3 44.2 10.03 18.93 5.52 10.41 3 

9 44.2 46.4 12.43 12.81 5.75 5.92 6 

10 46.4 47.5 4.85 5.66 4.40 5.14 2 

11 47.5 49.0 12.34 10.47 8.12 6.88 9 

12 49.0 49.97 3.95 5.14 4.29 5.58 5 

OR 224 ‐ Existing Conditions

IHSDM Crash Module Results by Group
Safety and Traffic Appendix D 

Historical Crash Data 

 
C M T PEOPLE

R O L O A S

T D M G S T K L P

I D W P T U V VEHICLE I I C E

SERIAL M A *COUNTY OR Y N Y COLL R E TYP/OWN L N O E

NO DATE E Y CITY NAME # T P CRASH LOCATION TYPE EVENT CAUSE ERROR F H #1 #2 L J H D

04464 10/20/2012 8A SA *Clackamas 1 MN R Clackamas Highway AT MP 31.49 FIX 067 12 WET 1 011 0 1 N N

02761 07/12/2014 8P SA *Clackamas 1 MN R Clackamas Highway AT MP 31.55 FIX 060,079 10 079 DRY 1 091 0 1 Y N

04673 10/10/2016 10A MO *Clackamas 1 MN R Clackamas Highway AT MP 31.62 OTH 081 12 WET 1 010 0 0 N N

02678 06/22/2015 1P MO *Clackamas 1 MN R Clackamas Highway AT MP 32.00 OTH 01 079,047 DRY 1 091 0 1 N Y

02550 07/14/2012 2P SA *Clackamas 1 MN R Clackamas Highway AT MP 32.50 FIX 079,010 16,32 080,052 DRY 1 011 0 1 N N

02613 07/18/2012 9P WE *Clackamas 1 MN R Clackamas Highway AT MP 32.85 FIX 035,079,010 12 083 DRY 1 011 0 2 N N

02469 06/29/2011 3P WE *Clackamas 1 MN R Clackamas Highway AT MP 32.91 FIX 124,079,086 01,32 047,052,080 DRY 1 091 0 1 Y Y

02387 07/04/2013 11A TH *Clackamas 1 MN R Clackamas Highway AT MP 32.91 SS-O 10 080 DRY 3 091 011 0 1 N N

00801 02/19/2016 1P FR *Clackamas 1 MN R Clackamas Highway AT MP 32.92 FIX 043,079 30 050,079 WET 1 011 0 1 N Y

02877 08/13/2010 1P FR *Clackamas 1 MN R Clackamas Highway AT MP 33.00 FIX 043 10 080 DRY 1 091 0 1 N N

02211 06/06/2017 4P TU *Clackamas 1 MN R Clackamas Highway AT MP 33.00 FIX 079,010 01,05 047,079 DRY 1 011 0 1 N Y

03384 08/20/2015 8P TH *Clackamas 1 MN R Clackamas Highway AT MP 33.17 FIX 079 10 079 DRY 1 011 0 0 N N

03932 07/16/2016 8P SA *Clackamas 1 MN R Clackamas Highway AT MP 33.25 HEAD 01 047,079,083 DRY 2 011 011 1 5 Y Y

03532 08/27/2017 3P SU *Clackamas 1 MN R Clackamas Highway AT MP 33.75 OTH 01 047,079 DRY 1 011 0 1 N Y

01636 04/28/2017 10A FR *Clackamas 1 MN R Clackamas Highway AT MP 33.93 FIX 072 01 047,079 WET 1 011 0 1 Y Y

03253 09/03/2011 6A SA *Clackamas 1 MN R Clackamas Highway AT MP 34.00 FIX 079 32,16 052,080,081 DRY 1 011 0 1 N N

04654 12/03/2011 5P SA *Clackamas 1 MN R Clackamas Highway AT MP 34.00 FIX 124,079,010 01 047,080 ICE 1 011 0 0 N Y

03268 09/05/2011 4P MO *Clackamas 1 MN R Clackamas Highway AT MP 34.20 TURN 02,01 047 DRY 2 011 011 0 6 N Y

01567 03/23/2018 3P FR *Clackamas 1 MN R Clackamas Highway AT MP 34.20 FIX 062,010 17,01 047,081 DRY 1 011 1 2 N Y

03142 08/24/2012 9P FR *Clackamas 1 MN R Clackamas Highway AT MP 34.82 FIX 035,079 10 083 DRY 1 011 0 0 N N

03493 09/30/2018 5P SU *Clackamas 1 MN R Clackamas Highway AT MP 34.82 FIX 043 10 083,080 DRY 1 011 0 3 N N

00094 01/10/2010 4P SU *Clackamas 1 MN R Clackamas Highway AT MP 35.17 HEAD 16,27 016,080 DRY 2 011 011 0 3 N N

03482 08/24/2017 12P TH *Clackamas 1 MN R Clackamas Highway AT MP 35.19 REAR 30,07 050,042 DRY 2 011 011 0 4 N Y

04117 10/02/2017 2P MO *Clackamas 1 MN R Clackamas Highway AT MP 35.67 FIX 079,001 01 047,079 DRY 1 091 0 1 N Y

03289 07/11/2012 9P WE *Clackamas 1 MN R Clackamas Highway AT MP 35.70 FIX 079 01 047,080 WET 1 011 0 0 N Y

01389 04/23/2011 12P SA *Clackamas 1 MN R Clackamas Highway AT MP 36.00 FIX 072 01 047,080,081 DRY 1 091 0 1 N Y

01566 04/29/2012 2P SU *Clackamas 1 MN R Clackamas Highway AT MP 37.00 FIX 079,001 01 047,080 DRY 1 091 0 1 N Y

02587 06/27/2015 9A SA *Clackamas 1 MN R Clackamas Highway AT MP 37.00 FIX 043 10 079 DRY 1 091 0 1 N N

Disclaimer: The information contained in this report is compiled from individual driver and police crash reports submitted to the Oregon Department of Transportation as required in ORS 811.720. The Crash Analysis and 

Reporting Unit is committed to providing the highest quality crash data to customers. However, because submittal of crash report forms is the responsibility of the individual driver, the Crash Analysis and Reporting Unit can not 

guarantee that all qualifying crashes are represented nor can assurances be made that all details pertaining to a single crash are accurate. Note: Legislative changes to DMV's vehicle crash reporting requirements, effective 

01/01/2004, may result in fewer property damage only crashes being eligible for inclusion in the Statewide Crash Data File.

OREGON DEPARTMENT OF TRANSPORTATION - TRANSPORTATION DEVELOPMENT DIVISION

TRANSPORTATION DATA SECTION - CRASH ANAYLYSIS AND REPORTING UNIT

CRASH LOCATION LIST

Highway 171 ALL ROAD TYPES, MP 31.0 to 49.97 01/01/2010 to 12/31/2019, Both Add and Non-Add mileage

07/07/2021

CDS390 Page: 1

1 - 28 of 95 Crash records shown.
C M T PEOPLE

R O L O A S

T D M G S T K L P

I D W P T U V VEHICLE I I C E

SERIAL M A *COUNTY OR Y N Y COLL R E TYP/OWN L N O E

NO DATE E Y CITY NAME # T P CRASH LOCATION TYPE EVENT CAUSE ERROR F H #1 #2 L J H D

03468 09/28/2018 12P FR *Clackamas 1 MN R Clackamas Highway AT MP 37.00 TURN 02,08 DRY 2 011 011 0 1 N N

01445 04/20/2015 11A MO *Clackamas 1 MN R Clackamas Highway AT MP 37.11 FIX 034,043 30 050,079 DRY 1 091 0 1 N Y

03744 10/08/2019 10A TU *Clackamas 1 MN R Clackamas Highway AT MP 37.19 FIX 034,062 10 083 WET 1 011 0 1 N N

02535 07/20/2018 8P FR *Clackamas 1 MN R Clackamas Highway AT MP 37.33 PED 10 079 DRY 1 091 0 1 N N

01785 06/02/2019 2P SU *Clackamas 1 MN R Clackamas Highway AT MP 37.42 FIX 126,001,128 10 079 DRY 1 091 1 0 N N

01748 05/05/2017 1A FR *Clackamas 1 MN R Clackamas Highway AT MP 37.45 FIX 003,079 10 079 WET 1 011 0 1 N N

02057 06/20/2019 6P TH *Clackamas 1 MN R Clackamas Highway AT MP 37.47 SS-M 05 083,079 DRY 2 011 011 0 5 N N

03249 08/10/2015 5P MO *Clackamas 1 MN R Clackamas Highway AT MP 37.49 FIX 043 30,05 050,079 DRY 1 011 0 1 N Y

03953 10/29/2018 6P MO *Clackamas 1 MN R Clackamas Highway AT MP 38.00 FIX 068 12 WET 1 010 0 0 N N

01581 04/07/2016 6P TH *Clackamas 1 MN R Clackamas Highway AT MP 38.34 FIX 043 30,05 DRY 1 010 0 0 N Y

00192 01/12/2016 5A TU *Clackamas 1 MN R Clackamas Highway AT MP 38.36 FIX 079,010 33 079,051 WET 1 011 0 1 Y N

03728 08/14/2016 5P SU *Clackamas 1 MN R Clackamas Highway AT MP 38.70 TURN 001 06,30 032,050 DRY 2 091 011 1 1 Y Y

00231 01/15/2017 12P SU *Clackamas 1 MN R Clackamas Highway AT MP 39.00 FIX 124,079,010 10 080 ICE 1 011 0 2 N N

00521 02/08/2012 7P WE *Clackamas 1 MN R Clackamas Highway AT MP 39.14 FIX 124,046 01 047 ICE 1 011 0 0 N Y

00771 02/29/2012 7A WE *Clackamas 1 MN R Clackamas Highway AT MP 39.22 FIX 124,079,010 01 047,080 ICE 1 011 0 1 N Y

02540 07/26/2019 4P FR *Clackamas 1 MN R Clackamas Highway AT MP 39.23 FIX 057,072 30 050,079 DRY 1 011 0 3 N Y

00806 03/04/2018 1P SU *Clackamas 1 MN R Clackamas Highway AT MP 39.97 FIX 062 01 DRY 1 010 0 0 Y Y

01958 05/22/2015 9P FR *Clackamas 1 MN R Clackamas Highway AT MP 40.00 FIX 068 12 DRY 1 011 0 2 N N

03065 04/15/2017 3P SA *Clackamas 1 MN R Clackamas Highway AT MP 40.24 FIX 079,010,001 01 047,079,080 DRY 1 091 1 0 N Y

01424 04/26/2011 12P TU *Clackamas 1 MN R Clackamas Highway AT MP 40.74 FIX 079 27 016,081 WET 1 011 0 2 N N

01381 03/26/2018 3P MO *Clackamas 1 MN R Clackamas Highway AT MP 41.28 FIX 079,062 05,01 047,079 WET 1 011 0 1 Y Y

02706 07/26/2013 6P FR *Clackamas 1 MN R Clackamas Highway AT MP 41.61 TURN 06,01 032,047 DRY 2 091 011 0 1 N Y

03311 08/13/2017 5P SU *Clackamas 1 MN R Clackamas Highway AT MP 42.17 FIX 062,087 16,32 080,052 DRY 1 011 0 2 N N

01806 05/27/2018 4P SU *Clackamas 1 MN R Clackamas Highway AT MP 42.48 FIX 069,079,072 10 083 DRY 1 011 0 1 Y N

01711 05/22/2010 1A SA *Clackamas 1 MN R Clackamas Highway AT MP 42.50 FIX 035,079 12 080 WET 1 011 0 1 N N

04517 10/28/2017 4P SA *Clackamas 1 MN R Clackamas Highway AT MP 42.70 FIX 079 10 079 DRY 1 091 0 1 N N

01768 05/10/2015 4P SU *Clackamas 1 MN R Clackamas Highway AT MP 43.17 FIX 043,001 01,05 047,079 DRY 1 091 0 1 N Y

03074 09/02/2018 2P SU *Clackamas 1 MN R Clackamas Highway AT MP 43.19 FIX 079 01 047,079 DRY 1 091 0 1 N Y

Disclaimer: The information contained in this report is compiled from individual driver and police crash reports submitted to the Oregon Department of Transportation as required in ORS 811.720. The Crash Analysis and 

Reporting Unit is committed to providing the highest quality crash data to customers. However, because submittal of crash report forms is the responsibility of the individual driver, the Crash Analysis and Reporting Unit can not 

guarantee that all qualifying crashes are represented nor can assurances be made that all details pertaining to a single crash are accurate. Note: Legislative changes to DMV's vehicle crash reporting requirements, effective 

01/01/2004, may result in fewer property damage only crashes being eligible for inclusion in the Statewide Crash Data File.

OREGON DEPARTMENT OF TRANSPORTATION - TRANSPORTATION DEVELOPMENT DIVISION

TRANSPORTATION DATA SECTION - CRASH ANAYLYSIS AND REPORTING UNIT

CRASH LOCATION LIST

Highway 171 ALL ROAD TYPES, MP 31.0 to 49.97 01/01/2010 to 12/31/2019, Both Add and Non-Add mileage

07/07/2021

CDS390 Page: 2

29 - 56 of 95 Crash records shown.
C M T PEOPLE

R O L O A S

T D M G S T K L P

I D W P T U V VEHICLE I I C E

SERIAL M A *COUNTY OR Y N Y COLL R E TYP/OWN L N O E

NO DATE E Y CITY NAME # T P CRASH LOCATION TYPE EVENT CAUSE ERROR F H #1 #2 L J H D

03619 09/30/2012 2P SU *Clackamas 1 MN R Clackamas Highway AT MP 43.25 NCOL 124 01 047,080 DRY 1 091 0 1 N Y

01740 05/22/2018 2A TU *Clackamas 1 MN R Clackamas Highway AT MP 43.25 FIX 068,079,010 10 079 DRY 1 011 0 2 N N

02240 06/27/2018 12A WE *Clackamas 1 MN R Clackamas Highway AT MP 43.25 OTH 035,079,072 30 050,079 DRY 1 011 0 2 Y Y

02095 06/23/2019 10A SU *Clackamas 1 MN R Clackamas Highway AT MP 43.26 FIX 034,079,010 05 083 DRY 1 011 0 2 N N

03524 09/13/2013 12P FR *Clackamas 1 MN R Clackamas Highway AT MP 43.27 OTH 124 10 083 DRY 1 091 0 1 N N

02588 08/05/2018 2P SU *Clackamas 1 MN R Clackamas Highway AT MP 43.51 FIX 079,010,001 01 047,081 DRY 1 091 1 0 N Y

01036 03/30/2019 6P SA *Clackamas 1 MN R Clackamas Highway AT MP 43.57 FIX 079,010 10 WET 1 010 0 0 N N

02683 08/02/2010 4P MO *Clackamas 1 MN R Clackamas Highway AT MP 43.80 NCOL 001,079 01 047,080 DRY 1 091 0 1 N Y

03182 08/07/2015 10P FR *Clackamas 1 MN R Clackamas Highway AT MP 43.81 OTH 33 079 DRY 1 011 0 1 Y N

03482 01/14/2018 6P SU *Clackamas 1 MN R Clackamas Highway AT MP 43.81 FIX 072,010 33 079,051 DRY 1 011 0 1 N N

00044 01/05/2014 8A SU *Clackamas 1 MN R Clackamas Highway AT MP 43.84 FIX 124,079,072 01 047,080 ICE 1 011 0 2 N Y

03493 09/23/2011 3P FR *Clackamas 1 MN R Clackamas Highway AT MP 44.95 FIX 062 02 083,081 DRY 1 011 0 1 N N

00129 01/10/2016 12P SU *Clackamas 1 MN R Clackamas Highway AT MP 45.32 FIX 124,062 10 079 ICE 1 011 0 1 N N

03522 06/08/2013 6P SA *Clackamas 1 MN R Clackamas Highway AT MP 45.50 OTH 124,001 10 083 DRY 1 091 0 1 N N

03722 09/27/2013 1P FR *Clackamas 1 MN R Clackamas Highway AT MP 45.50 FIX 079,010 01,32 047,080,052 WET 1 011 0 1 N Y

01171 03/29/2012 9P TH *Clackamas 1 MN R Clackamas Highway AT MP 45.78 FIX 043 01 047,081 WET 1 011 0 4 N Y

01868 06/05/2010 4P SA *Clackamas 1 MN R Clackamas Highway AT MP 45.79 FIX 043 27 016,080,081 DRY 1 011 0 2 N N

01221 03/28/2014 1P FR *Clackamas 1 MN R Clackamas Highway AT MP 45.80 FIX 078,043 25 083 WET 1 011 0 3 N N

04733 11/09/2015 11A MO *Clackamas 1 MN R Clackamas Highway AT MP 45.82 FIX 035,043,079 10 081 WET 1 011 0 0 N N

03461 08/19/2012 4P SU *Clackamas 1 MN R Clackamas Highway AT MP 46.03 FIX 079,010 16 081 DRY 1 011 0 3 N N

02320 06/13/2015 6P SA *Clackamas 1 MN R Clackamas Highway AT MP 47.56 FIX 043 10 080 DRY 1 011 0 1 N N

00149 01/13/2013 6P SU *Clackamas 1 MN R Clackamas Highway AT MP 47.57 FIX 124,079,010 01 047,080 ICE 1 011 0 0 N Y

02001 05/23/2017 11P TU *Clackamas 1 MN R Clackamas Highway AT MP 47.59 FIX 079,010 01,05 073,047,079 DRY 1 011 0 2 Y Y

90806 03/04/2018 1P SU *Clackamas 1 MN R Clackamas Highway AT MP 47.78 FIX 079 01,05 WET 1 010 0 0 Y Y

03020 07/25/2017 2P TU *Clackamas 1 MN R Clackamas Highway AT MP 48.06 FIX 079 01 047,079 DRY 1 091 0 1 N Y

04551 10/30/2017 2P MO *Clackamas 1 MN R Clackamas Highway AT MP 48.07 FIX 079,001,128 10 079 DRY 1 091 0 1 N N

01916 06/04/2018 10A MO *Clackamas 1 MN R Clackamas Highway AT MP 48.07 OTH 021,022 24,01 047,085,079 DRY 1 011 0 1 N Y

01795 03/31/2014 2P MO *Clackamas 1 MN R Clackamas Highway AT MP 48.55 FIX 079 01 079,047 DRY 1 091 0 1 N Y

Disclaimer: The information contained in this report is compiled from individual driver and police crash reports submitted to the Oregon Department of Transportation as required in ORS 811.720. The Crash Analysis and 

Reporting Unit is committed to providing the highest quality crash data to customers. However, because submittal of crash report forms is the responsibility of the individual driver, the Crash Analysis and Reporting Unit can not 

guarantee that all qualifying crashes are represented nor can assurances be made that all details pertaining to a single crash are accurate. Note: Legislative changes to DMV's vehicle crash reporting requirements, effective 

01/01/2004, may result in fewer property damage only crashes being eligible for inclusion in the Statewide Crash Data File.

OREGON DEPARTMENT OF TRANSPORTATION - TRANSPORTATION DEVELOPMENT DIVISION

TRANSPORTATION DATA SECTION - CRASH ANAYLYSIS AND REPORTING UNIT

CRASH LOCATION LIST

Highway 171 ALL ROAD TYPES, MP 31.0 to 49.97 01/01/2010 to 12/31/2019, Both Add and Non-Add mileage

07/07/2021

CDS390 Page: 3

57 - 84 of 95 Crash records shown.
C M T PEOPLE

R O L O A S

T D M G S T K L P

I D W P T U V VEHICLE I I C E

SERIAL M A *COUNTY OR Y N Y COLL R E TYP/OWN L N O E

NO DATE E Y CITY NAME # T P CRASH LOCATION TYPE EVENT CAUSE ERROR F H #1 #2 L J H D

02954 08/15/2011 12A MO *Clackamas 1 MN R Clackamas Highway AT MP 48.97 FIX 062 10 081 DRY 1 011 0 1 N N

03354 09/11/2011 8A SU *Clackamas 1 MN R Clackamas Highway AT MP 49.10 FIX 124,079,010 01 047,080 DRY 1 011 0 2 N Y

00803 03/04/2018 7A SU *Clackamas 1 MN R Clackamas Highway AT MP 49.80 FIX 124,062 01 047,079 ICE 1 011 0 1 N Y

04296 12/01/2019 10A SU *Clackamas 1 MN R Clackamas Highway AT MP 49.82 HEAD 124 01,05 047,079 ICE 2 011 011 0 2 N Y

02716 07/25/2012 4P WE *Clackamas 1 MN R Clackamas Highway AT MP 49.86 FIX 079,010 01,33 047,081,051 DRY 1 011 0 4 Y Y

03394 08/30/2014 1P SA *Clackamas 1 MN R Clackamas Highway AT MP 49.87 SS-M 05,01 080,047 WET 2 011 011 0 4 N Y

02428 07/06/2012 11A FR *Clackamas 1 MN R Clackamas Highway AT MP 49.88 SS-M 01,05,32 047,080,052 DRY 2 011 011 0 0 N Y

01941 05/21/2014 12A WE *Clackamas 1 MN R Clackamas Highway AT MP 49.88 FIX 043,046 01 047,080 DRY 1 011 0 0 N Y

02687 07/05/2014 8P SA *Clackamas 1 MN R Clackamas Highway AT MP 49.88 FIX 047,043 01,05 047,079 DRY 1 011 0 4 N Y

01793 05/06/2014 5P TU *Clackamas 1 MN R Clackamas Highway AT MP 49.89 FIX 043 30,05 050,080 DRY 1 011 0 1 N Y

03871 06/17/2012 1P SU *Clackamas 1 MN R Clackamas Highway AT MP 49.96 HEAD 001 30,05 050,080 DRY 3 091 011 1 0 N Y

Disclaimer: The information contained in this report is compiled from individual driver and police crash reports submitted to the Oregon Department of Transportation as required in ORS 811.720. The Crash Analysis and 

Reporting Unit is committed to providing the highest quality crash data to customers. However, because submittal of crash report forms is the responsibility of the individual driver, the Crash Analysis and Reporting Unit can not 

guarantee that all qualifying crashes are represented nor can assurances be made that all details pertaining to a single crash are accurate. Note: Legislative changes to DMV's vehicle crash reporting requirements, effective 

01/01/2004, may result in fewer property damage only crashes being eligible for inclusion in the Statewide Crash Data File.

OREGON DEPARTMENT OF TRANSPORTATION - TRANSPORTATION DEVELOPMENT DIVISION

TRANSPORTATION DATA SECTION - CRASH ANAYLYSIS AND REPORTING UNIT

CRASH LOCATION LIST

Highway 171 ALL ROAD TYPES, MP 31.0 to 49.97 01/01/2010 to 12/31/2019, Both Add and Non-Add mileage

07/07/2021

CDS390 Page: 4

85 - 95 of 95 Crash records shown.
Safety and Traffic Appendix E 

Existing Guardrail Locations 

 
Start MP End MP Side Offset

31.15 31.72 Right 6

31.74 32.87 Right 6

32.93 33.31 Right 6

33.4 33.42 Right 6

33.51 33.52 Right 6

33.76 33.82 Right 6

33.83 34.09 Right 6

34.23 34.49 Right 6

34.56 35.18 Right 6

35.42 35.72 Right 6

35.77 36.2 Right 6

36.27 36.94 Right 6

36.98 37.19 Right 6

37.23 37.45 Right 6

37.46 38.65 Right 6

38.66 38.69 Right 6

38.8 38.83 Left 6

39.07 39.12 Left 6

39.19 39.23 Left 6

39.19 39.23 Right 6

39.58 39.71 Right 6

39.75 40.01 Right 6

40.08 40.92 Right 6

41.44 41.47 Right 6

41.51 41.52 Right 6

41.78 42.14 Right 6

42.44 43.27 Right 6

43.29 44.04 Right 6

44.13 44.57 Right 6

44.58 44.59 Right 6

45.8 45.81 Left 6

45.8 45.81 Right 6

45.86 45.87 Left 6

45.86 45.87 Right 6

46.04 46.64 Right 6

49.89 49.9 Left 6

49.89 49.9 Right 6

Barrier
Safety and Traffic Appendix F 

Presentation to Yellowstone National Park on 

Roadside Parking Discouragement 
Shoulder Parking 

Solutions

Yellowstone NP is looking for permanent solutions to 

parking along roadway shoulders. Larger physical obsta

as logs and boulders have been used but can be con

hazards and create maintenance issues. The ideas l

signing, striping and physical obstacles that could be 

deter parking along the shoulder and other locati
Striping & Rumble Strips

Options:• Cross-hatch markings on shoulder• “No Parking” pavement markings• Wide or double edge line• Colored Pavement• Longitudinal Rumble StripsConsiderations:1. Maintenance needs2. Striping may not have high compliance or impact3. Rumble strips have noise 

restrictions Red transverse pavement markings 

at Hoover Dam
Signing

Options:No Parking signs (R7/R8 series)

• Signing could be standalone or a more 

comprehensive park signing plan

• Establish a park rule/law about where 

parking is or isn’t legal, that could be enforced. Install signing in several places throughout the park to notify drivers of rule. 

Considerations:1. Signs may not have high compliance2. Initial cost and maintenance of signs3. Aesthetics of signage4. Need enforcement effort for compliance 

MUTCD Chap
Physical Deterrents: Rocks & Bould

Options:Innovative idea: to create breakaway boulders that look real but are still crashworthy.Available products:• https://www.amazon.com/OutdoorEssentials-Faux-Rock-XLarge/dp/B00NOP1PAM(large plastic 

boulders that can be moved around)

• http://dinorentosstudios.com/fake-foamrock-10-x-10-x-12/ (foam boulders that 

weigh only 8 lbs!)

Considerations:

1. up to 12” are considered less hazardous 

in the Roadside Design Guide

2. Use smaller rocks within clear zone, 

blend to bigger rocks outside of clear zone

Yosemite – they are using little rocks closer to t

rocks further away

Near Grand Teton N
Physical Deterrents: Delineator

Options:• Shoulder delineators near Jenny 

Lake area in Grand Teton NP. 

• No Parking signs are 1’x1’Considerations:1. Maintenance2. Aesthetics 

Grand Teton NP- delineators with No Parking symbol signs 

Delineator with ‘No Parking’ symbol, seen in forest units
Physical Deterrents: Curb & Fenc

Considerations:1. Curbs affect drainage2. Fence should still be crashworthy 3. Curbs not practical in most rural areas

Golden Gate NRA near the Point Bonita Lighthouse parking area 

Low-profile curbs being used 
Physical Deterrents: Bollards & Whee

Considerations:1. Bollard considered hazard unless 

breakaway design (costly)

2. Wheel stops could be considered 

hazard

3. Poor aesthetics

Death Valley – wheelstops along a campground access road

Death Valley NP – No Parking 

visitor center p
Physical Deterrents: Vegetation

Considerations:1. Maintenance may be required2. Height of vegetation to not restrict 

sight distance

1:3 Foreslope Design

Options:• A Project Manager from the Denver 

Service Center has been recommending 1:3 foreslopes on some projects just to deter parking along the shoulder.

Considerations:1. Creates a roadside sa2. Unknown if it has be
88

Appendix B

Unstable Slope Gap Analysis and On-Site Ratings Assessment Technical 

Memorandum
158377846

 

M E M O R A N D U M

Western Federal Lands Highway Division

610 E. Fifth Street

Vancouver, WA 98661

DATE: August 06, 2021

TO: Jamie Lemon

Transportation Planner

FROM: Ryan Cole

Engineering Geologist

SUBJECT: Geotechnical Memo 30-21

Unstable Slope Data Gap Analysis

OR FLPP FS PLAN 2021(8)

OR 224 Corridor Study -Phase 1

Clackamas County, Oregon

INTRODUCTION

The Mount Hood National Forest in Clackamas County, Oregon (OR) experienced 

catastrophic wildfire events in September 2020. These events caused significant impacts to 

recreational use and multimodal travel within the region, particularly along OR State Highway

224. The OR 224 corridor between Promontory Park and Ripplebrook has been closed since 

September 2020 due to fire damages, but is expected to reopen in late-summer 2021. The 

U.S. Forest Service (USFS) has requested assistance from the Western Federal Lands 

Highway Division (WFL) of the Federal Highway Administration (FHWA) to complete an 

Existing Conditions Assessment of USFS lands within the OR 224 corridor to better 

understand the extent of post-wildfire conditions as they relate to future use and to assess 

transportation system resiliency and access within the National Forest. The Existing 

Conditions Assessment will be the first of a two phase Corridor Study for OR 224. The 

purpose of the Phase 1 – Existing Conditions Assessment is to evaluate and document 

current baseline conditions along the closed portion of OR 224. Information gathered during 

the post-wildfire baseline conditions assessment will be used to inform future study efforts that 

identify project-specific improvements. WFL will document these additional areas of in-depth 

study to be completed in Phase 2 – Planning and Environmental Linkages (PEL) Initial 

Scoping as part of the Phase 1 effort.
Page 2 of 24

PROJECT DESCRIPTION

The purpose of this memorandum is to review Existing Conditions of unstable slopes in the 

OR 224 corridor from the Mt. Hood National Forest Boundary at MP 31.56 to the intersection 

of Forest Service Road (FSR) 57 at approximately MP 50 to identify data gaps and determine 

where there may be potentially vulnerable transportation assets and areas along the corridor 

that require more detailed unstable slope ratings or condition assessments during Phase 2.

GEOLOGY

The corridor lies entirely within the Western Cascades Physiographic Province, which is 

characterized by older volcanic rocks, generally steep slopes, and large pre-historic (ancient) 

landslide deposits (Peck, et al., 1964; see Attachment 1 - Geologic Map of the Highway 224 

Corridor). There are four bedrock units that underlie the corridor, and all are approximately 

horizontally bedded. The oldest and lowest in position are sedimentary and volcaniclastic 

rocks of the Little Butte Volcanic Series (approximately 23 to 33.9 million years ago (Ma)) 

located in the upper reaches of the Clackamas River, from Three Lynx Creek at MP 45.87 to

the end of the corridor at the intersection of FSR 57. This unit is primarily composed of 

volcanic and volcaniclastic deposits, including volcanic tuffs, mudflows, and lava flows of 

basalt and andesite. Smith (1994) indicates that the unit consists of “clay-bearing 

volcaniclastic formations overlain by unaltered lava flows of andesite and basalt, a 

combination that contributed to large-scale landsliding during the late Pleistocene”, 

approximately 10 thousand years ago (Ka). The entire valley bottom contains large scale 

earthflow-type landslides that produce generally subdued topography as compared to the 

lower portion of the corridor. 

Overlying the Little Butte Volcanic Series are the Grand Ronde and Wanapum members of 

the Columbia River Basalt Group (approximately 15 to 17 Ma). These lava flows form steep 

cliffs along the Clackamas River from the beginning of the corridor at the Mt. Hood National 

Forest Boundary up to Three Lynx Creek. The basalt lava flows are generally resistant to 

erosion and form steep cliffs. However, there is a weak sedimentary interbed called the 

Vantage Member between the two lava flows. The Vantage Member is composed of ashy, 

volcanic sandstone and siltstone deposits and is a barrier to groundwater flow, resulting in 

increased pore-water pressure at the slope face where the unit is exposed. The resulting pore 

water pressure in some cases has created slope instability where large landslides occur. The 

Vantage Member typically forms a steep bench of loose, unconsolidated talus where the 

upper basalt flows have been removed by undercutting.

Immediately above the Columbia River basalts are interfingered (layered) deposits of the 

Rhododendron and Sardine Formations (approximately 10 to 17 Ma), which are composed of 

volcaniclastic deposits of mudflows, conglomerates, and ash tuffs, as well as basalt and 

andesite lava flows, respectively. These geologic units cap the ridges within the corridor, 

including Wanderer’s Peak, Soosap Peak, Fish Creek Mountain, and East Mountain. The 

material in the Rhododendron formation is easily eroded and is also prone to landsliding, 
Page 3 of 24

which occasionally initiates as debris flows in the steep tributaries of the aforementioned 

peaks into the Clackamas River. 

Overlying the Rhododendron and Sardine Formations are younger basaltic and andesitic 

volcanic lava flows of the High Cascades (approximately 1.2 to3.9 Ma). These geologic units 

are primarily found in the headwaters of tributaries of the Clackamas River East of the 

corridor, and generally cap the ridge tops, including Mount Mitchell and Oak Grove Butte.

Also within the corridor is a wide plateau known as “La Dee Flat”, north of the Clackamas 

River at Promontory Park. La Dee Flat has a low slope angle that generally precludes the 

development of landslides.

SITE CONDITIONS

Lower Corridor – Forest Boundary to Three Lynx Creek

Loss of vegetation from the fire has destabilized talus slopes on benches as well as on alluvial 

fan deposits along the base of the Columbia River basalts in the lower portion of the corridor. 

Increases in rockfall have occurred and should be anticipated to continue along the corridor

from the Forest boundary to Three Lynx Creek. Additionally, debris flow potential exists where 

easily erodible deposits of Rhododendron formation overlie steep valley walls of Columbia 

River basalt. Modelling results provided by the U.S. Geological Survey (USGS) (Staley and 

Kean, 2020) indicate that streams crossing the highway in this section of the corridor are 

generally at moderate to high hazard for debris flows. 

Upper Corridor – Three Lynx Creek to FSR 57

Increases in soil moisture related to a decrease of evapotranspiration from a loss of 

vegetation has the potential to reinitiate and/or accelerate earthflows in the upper portion of 

the corridor from Three Lynx Creek to FSR 57, although this is anticipated to be minor over 

the course of the next five to ten years as vegetative cover increases. This has the potential to 

lead to increased deformation and subsidence of the paved surface of the roadway. 

Additionally, increased surface runoff on the earthflows could lead to significant erosion and 

sedimentation, which would negatively impact transportation infrastructure (roads, ditches, 

culverts). Streams draining this area are generally at a low hazard for debris flows (USGS, 

2020). 

ANALYSIS METHODOLOGY

This analysis was conducted as a desktop exercise that relied exclusively on existing data to 

identify two classes of unstable slopes:

1. Unstable slopes with ratings and/or assessments

2. Unstable slopes, or potentially unstable slopes without ratings and/or assessments
Page 4 of 24

The intent was to identify vulnerable transportation assets and identify areas along the 

corridor that require more detailed unstable slope ratings or condition assessments during 

Phase 2. The analysis relied primarily on two existing data sources:

1. Oregon Department of Transportation’s (ODOT) Unstable Slope Rating System 

(USRS) database

2. USGS’s Emergency Assessment of Post-Fire Debris-Flow Hazards debris flow 

modelling

ODOT’s USRS analyzes slopes adjacent to state highways for potential impacts that a failure 

could cause. Such failures include landslides, rockfall, and fill settlement or failures. 

Historically, ODOT has evaluated rock fall hazards, but has expanded the program to include 

other (soil) types of unstable slopes (landslides and debris flows). Under the revised program, 

ODOT is able to include economic factors in its analysis as well as hazard and engineering 

considerations so that sensible repair priorities can be more easily obtained.

The USGS conducts post-fire debris-flow hazard assessments for select fires in the Western 

United States, utilizing geospatial data related to basin morphology, burn severity, soil 

properties, and rainfall characteristics to estimate the probability and volume of debris flows 

that may occur in response to a design storm event. 

This analysis attempts to identify locations of debris flow prone unstable slopes or areas 

where debris flows could occur and are lacking unstable slope rating or site condition 

assessment data. These areas are clearly delineated where no unstable slope rating data 

exist and USGS modelling identified channels at moderate to high hazard for debris flow 

initiation. For this effort, we focused on stream channels that exhibited channel morphology 

(geology, grade, length, depth of incision, coalescing fan deposits, levies, anastomosing

channels, etc.) and observed past debris flow events that supported potential for future debris 

flow events. If channels met those criteria, based on geo-practitioner judgment, a 

recommendation to rate the unstable slopes was made. If the channel met the above criteria, 

but did not include observation of past debris flow events, a recommendation to perform a site 

condition assessment was made. 

This analysis assumes that potentially unstable slopes that have not been assessed and rated

by ODOT will be assessed and rated utilizing the Unstable Slope Management Program for 

Federal Land Management Agencies (USMP, FLH 2019) in Phase 2. In order to combine data 

from the two systems, and be useful in a geotechnical asset management framework, a 

crosswalk between the rating systems must be established so that ranking of sites can be 

accomplished utilizing ratings from either system. The crosswalk would assist in an “apples to 

apples” comparison of ratings so that sites can be ranked and prioritized for potential risk 

reduction measures. Therefore, a sample of unstable slopes in the corridor, rated utilizing the 

USRS, should be rerated with FLH’s USMP prior to the rating of new unstable slopes utilizing

the USMP. Rerating of ODOT USRS rated unstable slopes should include a range of different 

unstable slope types (landslide, rockfall, debris flow, etc.) from a low to high risk, and should 

focus on slopes that include a STIP score, which is the score used for project identification 
Page 5 of 24

and prioritization for ODOT. This additional level of effort is strongly recommended for Phase 

2.

Results

ODOT’s USRS consists of 45 pre-fire unstable slope ratings conducted between 2007 and 

2009, as well as 42 post-fire assessments (non-ratings) completed in 2020, which included 13 

new unstable slope assessments that did not have a rating associated with them. The postfire assessments reassessed 30 (67%) of the pre-fire unstable slopes, for a total of 58 ODOT 

pre and post-fire ratings and/or assessments of unstable slopes within the study corridor. Prefire unstable slope ratings included 30 rockfall sites, 14 road fill failures, and five landslides. 

The new slope assessments focused primarily on rockfall (see Attachment 2 - Unstable 

Slopes Existing Condition and Data Gaps Maps, and Attachment 3 - Table of Unstable Slopes 

with USRS Ratings). 

The USGS modeled debris flow hazard for 84 streams that intersect the highway within the 

study corridor, which ranged from low to high (see Attachment 2 - Unstable Slopes Existing 

Condition and Data Gaps Maps). Generally, streams in the lower corridor were modelled as

moderate to high hazard, while streams in the upper corridor were modelled as low to 

moderate hazard. This is interpreted as being controlled by the presence of differing geology 

and the associated basin morphology between the upper and lower corridor.

Lower Corridor – Forest Boundary to Three Lynx Creek

ODOT identified and rated 41 unstable slopes in the lower corridor. Communication with 

ODOT identified four unstable slopes that were not assessed in the post-fire effort but would 

benefit from completing a more detailed rating. The USGS modeled 73 stream segments for 

debris flows hazard in the lower corridor, and 37 (51%) were rated at high hazard, 34 (47%) 

moderate hazard, and 2 (3%) low hazard. Analysis of unrated, debris flow prone channels 

identified two unstable slopes that should also be rated, and eight sites where condition 

assessments should be performed. 

Upper Corridor – Three Lynx Creek to FSR 57

ODOT identified and rated ten unstable slopes in the upper corridor. Communication with 

ODOT identified four unstable slopes that were not assessed in the post-fire effort but would 

benefit from completing a more detailed rating. There is a lack of slope ratings in the upper 

section of the corridor, which may indicate that there is minimal geologic hazard present in this 

area due to the generally subdued topography. The USGS modelled 13 stream segments for 

debris flows hazard in the upper corridor and had generally low to moderate hazard. Analysis 

of unrated, debris flow prone channels identified one unstable slope that should also be rated. 
Page 6 of 24

RECOMMENDATIONS

Conduct a crosswalk of USRS rated unstable slopes by rerating both types of unstable slope

with the USMP in order to compare ratings between the two systems so that sites can be 

ranked and prioritized for potential risk reduction measures. Utilize the USMP; (FLH, 2019) to 

rate identified unstable slopes where data gaps exist. This includes eight sites recommended 

by ODOT, three high hazard debris flow channels where past debris flow events have been 

observed, and the approximately five miles of the upper corridor from Three Lynx Creek to 

FSR 57 (see Attachment 4 - Table of Unstable Slopes Requiring USMP Ratings or Site 

Condition Assessments). Additionally, perform site condition assessments on eight high 

hazard debris flow prone channels where past debris flow events have not been observed.

These data could be used to inform future study efforts that identify project-specific 

improvements to make OR 224 a more resilient transportation corridor. 

REFERENCES

Federal Lands Highway, 2019, Unstable Slope Management Program for Federal Land 

Management Agencies, FHWA-FLH-19-002.

Oregon Department of Transportation, 2020, Unstable Slopes Rating System Database, data 

provided by ODOT on April 29, 2021 and July 19, 2021, respectively.

Peck, D.L., Griggs, A.B., Schlicker, H.G., Wells, F.G., and Dole, H.M, 1964, Geology of the 

central and northern parts of the western Cascade Range in Oregon: U.S. Geological 

Survey PP-449, scale 1:250,000.

Smith, D.A., 1994, Soil Properties and Behavior of Earthflows in the Mt. Hood National Forest, 

Oregon. Portland State University: Dissertations and Theses. Paper 4779.

Staley, D.M, and Kean, J.W., 2020, Emergency assessment of post fire debris flow hazards, 

Riverside an White River Fires (Mt. Hood National Forest): U.S. Geological Survey 

https://landslides.usgs.gov/hazards/postfire_debrisflow/. 

Walker, G.W., and MacLoed, N.S., 1991, Geologic Map of Oregon: U.S. Geological Survey, 

1:500,000 scale. 

U.S. Department of Agriculture Forest Service, 2020, Riverside and White River Fires Burned 

Area Emergency Response Geologic Hazards Assessment. 

CLOSING

Please contact Ryan Cole at (360) 619-7571 or ryan.cole@dot.gov with any questions 

regarding this memorandum.

INITIALS

CC: Douglas A. Anderson, WFL Geotechnical Functional Manager

Geotechnical File

Attachments: 

1. Geologic Map of the Highway 224 Corridor

2. Unstable Slopes Existing Condition and Data Gaps Maps (9 figures)
Page 7 of 24

3. Table of Unstable Slopes with USRS Ratings

4. Table of Unstable Slopes Requiring USMP Ratings or Site Condition Assessments
Page 8 of 24

ATTACHMENT 1 - GEOLOGIC MAP OF THE HIGHWAY 224 CORRIDOR
Page 9 of 24

Geologic Map of the area of the Highway 224 corridor impacted by the Riverside Fire (modified from Peck, et al., 1964).
Page 10 of 24

ATTACHMENT 2 - UNSTABLE SLOPES EXISTING CONDITION

AND DATA GAPS MAPS (9 FIGURES)
Page 11 of 24
Page 12 of 24
Page 13 of 24
Page 14 of 24
Page 15 of 24
Page 16 of 24
Page 17 of 24
Page 18 of 24
Page 19 of 24
Page 20 of 24

ATTACHMENT 3 - TABLE OF UNSTABLE SLOPES WITH USRS RATINGS
Page 21 of 24

Table 1. Rated and/or assessed unstable slopes; italicized rows indicate that unstable 

slope was reassessed after the 2020 Riverside Fire.

Record ID M Begin MP End MP Unstable Slope Type

SL171-0031-85LW1 31.85 31.82 31.88 Rockfall

SL171-0031-95LW1 31.95 31.88 32.02 Rockfall

SL171-0032-07LW1 32.07 32.03 32.11 Rockfall

SL171-0032-17RE1 32.17 32.16 32.18 Fill Failure

SL171-0032-18LW1 32.18 32.15 32.21 Rockfall

SL171-0032-37RE1 32.37 32.36 32.38 Fill Failure

NEW SITE - 32.50 32.75 Soil Raveling

SL171-0032-96LW1 32.96 32.92 33.00 Rockfall

SL171-0033-03LW1 33.03 33.01 33.05 Rockfall

SL171-0033-11LW1 33.11 33.05 33.17 Rockfall

SL171-0033-83LW1 33.83 33.79 33.87 Rockfall

NEW SITE - 33.91 34.03 Rockfall

NEW SITE - 34.32 34.35 Rockfall

NEW SITE - 34.50 34.70 Soil Raveling

SL171-0034-83LW1 34.83 34.71 34.95 Rockfall

SL171-0035-56LW1 35.56 35.50 35.62 Rockfall

SL171-0035-66LW1 35.66 35.65 65.67 Rockfall

SL171-0036-41LW1 36.41 36.33 36.49 Rockfall

SL171-0036-68LW1 36.68 36.62 36.74 Rockfall

NEW SITE - 36.90 36.94 Debris Flow

SL171-0037-36LW1 37.36 37.29 37.43 Rockfall

NEW SITE - 37.45 37.48 Rockfall

NEW SITE - 37.65 37.80 Rockfall

SL171-0037-88RE1 37.88 37.87 37.89 Fill Failure

SL171-0039-28LW1 39.28 39.23 39.33 Rockfall

SL171-0039-66LW1 39.66 39.65 39.67 Rockfall

SL171-0039-75LW1 39.75 39.67 39.83 Rockfall

SL171-0040-30LW1 40.30 40.27 40.33 Rockfall

SL171-0040-44LW1 40.44 40.42 40.45 Rockfall

SL171-0040-50LW1 40.50 40.48 40.51 Rockfall

SL171-0040-78LW1 40.78 40.74 40.82 Rockfall

SL171-0041-33LW1 41.33 41.25 41.41 Rockfall

SL171-0041-95LW1 41.95 41.80 42.10 Rockfall

SL171-0042-60LW1 42.60 42.45 42.75 Rockfall

SL171-0042-82LW1 42.82 42.76 42.88 Rockfall

SL171-0042-86RE1 42.86 42.85 42.87 Fill Failure

SL171-0042-90RE1 42.90 42.89 42.91 Fill Failure

NEW SITE 43.00 - - Rockfall

SL171-0043-34LW1 43.34 43.21 43.47 Rockfall

SL171-0043-59LW1 43.59 43.51 43.67 Rockfall

SL171-0044-07LW1 44.07 44.04 44.10 Rockfall
Page 22 of 24

Record ID M Begin MP End MP Unstable Slope Type

SL171-0044-21LW1 44.21 44.14 44.27 Rockfall

SL171-0044-38LW1 44.38 44.29 44.47 Rockfall

NEW SITE - 44.95 45.00 Rockfall

NEW SITE - 45.15 45.16 Rockfall

SL171-0045-20LW1 45.20 45.20 45.21 Fill Failure

SL171-0045-24LW1 45.24 45.24 45.25 Fill Failure

SL171-0045-24RE1 45.24 45.24 45.25 Landslide

SL171-0045-28RE1 45.28 45.28 45.29 Fill Failure

SL171-0045-33LW1 45.33 45.32 45.34 Fill Failure

SL171-0045-37LW1 45.37 45.36 45.38 Fill Failure

NEW SITE - 45.40 45.60 Rockfall

SL171-0045-47LW1 45.47 45.41 45.53 Fill Failure

SL171-0046-23RE1 46.23 46.20 46.26 Fill Failure

SL171-0046-29LW1 46.29 46.26 46.33 Fill Failure

NEW SITE - 46.30 46.37 Rockfall

SL171-0048-26RE1 48.26 48.24 48.28 Fill Failure

NEW SITE - 48.69 48.69 Rockfall
Page 23 of 24

ATTACHMENT 4 - TABLE OF UNSTABLE SLOPES REQUIRING USMP RATINGS OR 

SITE CONDITION ASSESSMENTS
Page 24 of 24

Table 2. Unstable slopes identified as requiring USMP ratings or site condition assessments. 

Record ID MP Begin MP End MP Unstable Slope Type Source Recommendation; Notes

1 32.56 - - Landslide, debris flow ODOT/USGS RISK RATING; ODOT identified soil raveling at MP 32.50-32.75, 

H DF haz., channel geometry

2 33.26 - - Landslide, debris flow USGS RISK RATING; observed DF

3 33.32 - - Landslide, debris flow USGS RISK RATING; observed DF

4 - 36.00 36.05 Landslide, debris flow USGS SITE CONDITION ASSESSMENT; M DF haz., channel geometry

5 36.89 Landslide, debris flow ODOT RISK RATING; post-fire debris flows 01/2021 and 05/2021, 

includes rockfall in a 100-yard long zone

6 38.03 - - Landslide, debris flow USGS SITE CONDITION ASSESSMENT; M DF haz., channel geometry

7 40.53 - - Landslide, debris flow USGS SITE CONDITION ASSESSMENT; H DF haz., channel geometry

8 40.65 - - Landslide, debris flow USGS SITE CONDITION ASSESSMENT; M DF haz., channel geometry

9 - 42.72 42.78 Landslide, translational ODOT RISK RATING; cracks/offsets in pavement - bin wall rotation

10 42.95 - - Landslide, erosional ODOT RISK RATING; slope erosion has crept close to the road prism

11 43.52 - - Landslide, debris flow USGS SITE CONDITION ASSESSMENT; H DF haz., channel geometry

12 43.70 - - Landslide, debris flow USGS SITE CONDITION ASSESSMENT; H DF haz., channel geometry 

13 43.91 - - Landslide, debris flow USGS SITE CONDITION ASSESSMENT; M DF haz., channel geometry

14 44.38 - - Landslide, debris flow USGS SITE CONDITION ASSESSMENT; H DF haz., channel geometry

15 45.81 - - Landslide, debris flow USGS SITE CONDITION ASSESSMENT; H DF hazard, channel geometry

16 - 46.23 46.30 Landslide, rotational ODOT RISK RATING; showing continued gradual movement from 

slope instability, west of tieback wall

17 - 46.30 46.40 Rockfall? ODOT RISK RATING; cutslope not in inventory

18 47.6

- - Rockfall/landslide?

ODOT

RISK RATING; no evidence of issues, but could become 

unstable

19 - 48.60 48.78 Rockfall? ODOT RISK RATING; scaled chute at MP48.69 after fire and the crest 

of that slope from the chute eastward to about MP 48.71

20 - 45.87 49.92 CORRIDOR WFLHD RISK RATING; 5 miles of the corridor may lack ratings
113

Appendix C

Hydrology Gap Analysis Technical Memorandum
Memorandum

Western Federal Lands Highway Division

610 E. Fifth Street

Vancouver, WA 98661-3801

TO: Jamie Lemon, WFLHD Transportation Planner 

FROM: James Neighorn, WFLHD Hydraulic Engineer 

DATE: September 7, 2021 

SUBJECT: OR FLPP FS PLAN 2021(8) – OR 224 Corridor Study Phase 1 

Draft Hydraulics Data Gap Analysis

INTRODUCTION

The Riverside fire was one of several catastrophic wildfire events which occurred across the 

Mount Hood National Forest, Oregon in 2020. The fire occurred within the Clackamas River 

basin and caused significant impacts along the Oregon State Route 224 corridor between 

Promontory Park and Ripplebrook. The U.S. Forest Service (USFS) is assessing the postwildfire conditions along this corridor and has requested assistance from Western Federal Lands 

Highway Division (WFL) of the Federal Highway Administration (FHWA). As part of the 

initial two-phased effort, an existing conditions assessment is being conducted to identify and 

document available information along the OR 224 corridor which can then be used to inform 

future study efforts for identifying project-specific improvements. 

BACKGROUND

The purpose of this memorandum is to provide a hydrologic and hydraulic corridor assessment 

that identifies available data, evaluates the suitability of the data, and identifies data or 

information gaps. 

A desktop review of available post-fire reports, as-built information, maintenance/inspection 

data, basin maps, and U.S. Geological Survey (USGS) post fire debris flow hazard mapping 

was conducted to identify drainage structures, flood and debris flow prone areas, transportation 

infrastructure, and facilities which may be impacted by post fire flows through and downstream 

of the corridor. 

AVAILABLE DATA AND SUITABILITY

The USFS Rapid Assessment Team evaluated the fire and completed a report, dated October

2020, which provided basal area mortality maps, summarized conditions, and provided action 

recommendations. A Burned Area Emergency Response (BAER) team began work on 

assessing the post-fire effects in September 2020. The team developed reports that include 

comprehensive information which will support the OR 224 corridor assessment. 
 

Page 2 of 13 

Burned Area Reflectance Classification (BARC), aerial reconnaissance data, and on-the-ground 

surveys were conducted to develop a Soil Burn Severity (SBS) map which was used to estimate

the soils post-fire hydrologic responses and resulting flows for the Clackamas River 

subwatersheds. Risk of upland erosion, sedimentation delivery rates, and increased flood flows

were then estimated for 27 subwatersheds using the Water Erosion Prediction Project (WEPP) 

Post-Fire Erosion Predictor (PEP). This was compared to pre-fire 5-year recurrence interval 

flood conditions to identify levels of risks at road/stream crossings. The BAER report provides 

analysis results of crossing points along OR 224 listed in Table 1. Significant increase in flow 

are predicted for a majority of the analyzed crossings.

Table 1. 

Crossing Points Pre-fire 

Q5 (cfs)

Post-fire

Q5 (cfs)

% 

Increase

Times 

Increase

Pre-fire 

Q50 (cfs) Acres

Moore Creek 380 390 3% 1.0X 530 459

Unnamed Tributary 110 240 118% 2.1X 340 171

Murphy Creek 180 250 39% 1.3X 270 257

Unnamed Creek 99 190 92% 1.9 X 170 133

Three Lynx Bridge 340 590 74% 1.7X 1300 1,675

Deer Creek 140 270 93% 1.9X 320 200

Dinner Creek 430 680 58% 1.5X 1200 921

Roaring River 7400 8300 12% 1.1X 15000 27,229

 

The burn area mortality, soil burn severity, subwatershed, and subwatershed peak stream flow 

analysis point maps developed by the BAER team have been included in Appendix A. 

The USGS conducted a post-fire debris-flow hazard assessments using the post-fire data and 

developed mapping. They utilized geospatial data related to basin morphology, burn severity, 

soil properties, and rainfall characteristics to estimate the probability, volume, and combined 

hazard rating of debris flows at both the drainage-basin scale and in a spatially distributed 

manner along the drainage network within each basin. The debris flow hazard mapping can be 

found on the following USGS website which includes downloadable shapefiles and geodatabase 

information: (https://landslides.usgs.gov/hazards/postfire_debrisflow/detail.php?objectid=309) 

The USGS model identifies 84 streams that intersect the highway within the study corridor. 

This includes those crossing points listed in Table 1. Due to differences in geology and basin 

morphology, the 73 streams modelled in the lower corridor between the forest boundary and 

Three Lynx Creek rated as moderate to high hazard. The 13 streams modelled in the upper 

corridor from Three Lynx Creek to Forest Road 57 rated as low to moderate hazard. 

Within the lower corridor there were 37 stream intersects that rated as high hazard. Although a 

handful of these where points modeled for flow in Table 1, additional flow modeling for the 

remaining crossings were not performed or unavailable. 
 

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The Oregon Department of Transportation (ODOT) was able to provide data on crossing

structures for a portion of the lower corridor from the forest boundary to Mile Point (MP) 36 

just south of Moore Creek. Beyond this point ODOT did not have inspection data for crossing 

structures, but only had culverts listed on plans. Since ODOT restricts outside access to their 

GIS database, the data provided was in spreadsheet format with information limited to specified 

queries. Additional asbuilt, inspection, and maintenance data for culverts along the corridor are 

available from the USFS. Per discussions with USFS staff, this data would need to be obtained 

from isolated databases and possibly from multiple sources. Current post-fire inspection 

information for crossing structures was not available. 

ODOT provided asbuilt plans and inspection reports, in electronic pdf format, for all bridges 

within the corridor which are listed in Table 2. The table does include three large culverts (Bull 

Creek, NF Clackamas, and Dry Creek) that fall within the recording requirements of the 

National Bridge Inventory System (NBIS). 

Table 2. 

Bridge No. Mile Post Description

Scour Critical

Rating

18178 41.48 Roaring River Bridge

18619 47.70 Bull Creek Culvert

05269 49.96 Clackamas River (Oak Fork Ripple Brook Br) 3

05272A 30.04 North Fork Clackamas River (Steel Plate Culvert)

08988 38.77 Clackamas River (Carter Br)

08989 39.15 Clackamas River (Armstrong Br) 3

08990 45.83 Clackamas River (Cripple Creek Br) 3

08991 44.88 Clackamas River (Three Lynx/Whitewater Br) 3

08992 49.12 Dry Creek Culvert

Review of the inspection reports revealed that four (4) of the bridges within the corridor have a 

National Bridge Inventory System (NBIS) scour critical rating of 3. This means that these 

structure’s foundations have the potential to be undermined by stream scour or erosion. The 

expected post-fire changes in flow conditions, debris loads, and sediment loads has the potential 

to increase scour and erosion resulting in a higher risk for the bridges becoming unstable. 

ODOT performed inspections of the bridges along the corridor in August of 2019. Another 

inspection is scheduled for this year. Inspection photos are available within the ODOT GIS 

database and can be provided upon request but would need to address large file transfer 

requirements. 

In addition to the analysis and recommendations included in the USFS BAER team reports, 

ODOT requested that the Federal Emergency Management Agency’s Erosion Threat 

Assessment/Reduction Team (ETART) produced a separate report to assess State, local, and 

private lands outside of the forest. This report re-affirms much of the recommendations made 

by the BAER team, but also adds recommendations for property and facilities affected 

downstream of the forest boundary. 
 

Page 4 of 13 

CORRIDOR NEEDS AND DATA GAPS

After review of available data and related report recommendations, the following hydrologic 

and hydraulic related needs and data gaps have been identified for the OR 224 corridor. 

Roadway Drainage and Culverts

ODOT is currently removing debris, removing danger trees, and storm proofing (cleaning 

ditches, culverts, repairing drainage) along the corridor to address immediate hazard concerns. 

However, hazardous conditions will continue to develop over the next 5 years as the loss of 

vegetation will allow normal storms to more easily cause erosion and debris flows on the steep 

roadside slopes resulting in further plugging of ditches and culverts, and/or washouts of

drainage facilities or stream crossings. The BAER and ETARTS reports recommend a number 

of drainage and culvert related actions to address or help reduce impacts from these expected 

hazards during the period in which vegetation recovers. 

A prioritized mitigation action plan should be prepared that identifies the most susceptible 

drainage crossings impacted by increased flow and debris. Pre-fire and post-fire flow modeling 

has been performed on only a small number of crossings (see Table 1) within the corridor. 

Flow modeling of additional crossings would assist in identifying culverts that may now be 

undersized or less able to accommodate plugging. Modeling may involve pre-fire and post-fire 

flow analysis or just post-fire regression flow analysis. Crossings located at high and/or 

moderate debris flow potential sites should also be evaluated to determine the resulting risk and 

hazard that debris flows may have at each site. 

Creating a complete inventory of drainage structures within the corridor (including condition 

assessments, documented maintenance issues, fish barrier issues, and geographic reference data) 

will be needed to produce a comprehensive mitigation plan and conduct flow analysis. This 

effort will also help identify structures needing to be replaced (specifically within the next 5-

years), identify sites that may be more prone to debris/plugging, and assist crews in locating 

structures in the field. Conducting site specific field evaluations may also be needed to begin 

identifying and prioritizing mitigation actions. Mitigation actions may include, but are not 

limited to, the following: 

• Culvert replacements or modifications to increase capacity (replacements should be 

sized on predicted increase in flows or fish passage requirements). 

• Installation of additional culverts at high risk locations. 

• Placement of upstream structures to deflect or catch debris away from the roadway. 

• Installation of slotted riser pipes, debris racks, and culvert end sections where feasible 

to reduce sediment and debris plugging. 

• Roadway embankment armoring in areas at risk for overtopping. 

• Drainageway improvements at crossings to reduce or eliminate streamflow diversion 

potential.

Bridges 

Post fire flow analysis indicates that increases in flow along the lower Clackamas River may not 

have a significant impact on bridges along the OR 224 corridor. Over the next 5 years,
 

Page 5 of 13 

significant amounts of eroded fine sediment will be deposited in draws, stream and river 

channels, and floodplains. This increased loading can result in aggradation and channel 

migration at bridges. Large woody debris will also accompany the initial flush of fine 

sediments and ash that is delivered to bridges along the corridor during high-intensity rain 

events over the next 5-years. This will greatly increase potential for debris jams to form around 

bridge abutments leading to significant increases in the potential for scour to undermine piers 

and abutments. Debris flow potential from Fish Creek and smaller drainages adjacent to the 

bridges may also impact the flow patterns at bridge crossings which can lead to increases in 

erosion and scour. 

It will be important to perform a post-fire evaluation of the four bridges rated as scour critical. 

Evaluation of the remaining bridges may also be warranted. The level of risk posed by

increased debris jams, changes to flow patterns, aggradation, and channel migration should be 

re-evaluated. The evaluations will require collecting pre-fire and post-fire photos, measuring 

channel conditions, identifying existing scour counter measures, and documenting scour 

conditions near abutments and piers. This information will not only be useful in evaluating the 

risk but will allow inspectors to identify changing conditions more readily after significant 

storm events. 

Identification and prioritization of additional site-specific monitoring efforts and preventative 

measures should consider the following: 

• Increasing bridge inspection intervals.

• Additional emergency storm monitoring and response plans. 

• Post-storm scour, damage, and debris inspection and assessment. 

• Installing additional scour countermeasures. 

• Monitoring movement of large woody debris and debris removal plans. 

• Installation of real-time water surface elevation and/or scour monitoring devices to 

alleviate staff limitations. 

• Signing and temporary emergency closure plans. 

Facilities and Properties

The review teams identified a high risk to Get-N-Go Promontory Marina and North Fork 

Reservoir Dam from woody debris build up. Increasing inspection frequency will be needed to 

identify debris removal. Staging, storage, and disposal areas will need to be identified and 

coordinated. 

The primary access to the Portland General Electric (PGE) Oak Grove Powerhouse is also 

vulnerable to debris flow from Three Lynx Creek. Mitigation actions that could be considered 

for this location could include placement of upstream debris racks, additions culverts, or 

armoring of the roadway. Additionally, an emergency response and access plan should be 

developed in coordination with PGE. 

Water Supply 

The Riverside Fire burned a large part of the municipal watershed of the City of Estacada and 

has the potential to impact other downstream municipal water supplies that have intakes on the 
 

Page 6 of 13 

Clackamas river including City of Lake Oswego, Clackamas River Water, Clackamas Water 

District, North Clackamas County Water Commission, and South Fork Water Board 

municipalities. 

During and after high-intensity storms, turbidity, dissolved organic carbon, nitrate, and some 

metals may likely increase by large magnitudes downstream of the burned area. Increases of 

such magnitude can pose problems for water-supply reservoirs and drinking-water treatment 

plants that can last many years and affect chemical treatment requirements, sludge volumes, and 

operating costs. 

Starting coordination with the affected municipalities to assess capacity of facilities to address 

post-fire water quality will assist in identifying if additional water quality monitoring within 

Clackamas River is needed to help managers. This could provide data to better estimate affects 

to operations and allow them to minimize effects through temporary diversions or changes to

water intakes. 

Watershed

The ETARTS team recommends installation of one or more near real-time (NRT) precipitation 

gages in or near the burn area. A NRT gage provides invaluable information about the localized 

intensity and amount of precipitation as it happens. Based on these data, the National Weather 

Service (NWS) can issue alerts to emergency managers, road crews, and other partners to warn 

of increased potential for flooding and debris flows that could threaten lives or damage homes, 

roads, and other infrastructure. Further developing gaging station data with rainfall data 

relations can assist with future evaluations of post-fire flood magnitude and hydrologic response 

in ungaged. 

The specific locations for possible NRT gages and funding sources will need to be evaluated

and coordinated between agencies. 

RECOMMENDATIONS 

The following summarizes recommended actions that will assist in completing data or 

information gaps for future study efforts in identifying project-specific improvements: 

• Develop a comprehensive drainage crossing inventory that includes post-fire condition 

inspections, emergency maintenance history, fish barrier information, and 

georeferenced location mapping. 

• Conduct detailed post-fire hydrologic and hydraulic analysis on identified elevated risk 

crossings. 

• Conduct site specific field evaluations of crossings affected by significant increased 

flow and within high risk debris flow areas. 

• At bridge crossings, collect pre-fire and post-fire photos, measure channel conditions, 

identify existing scour counter measures, and documenting scour conditions at 

abutments and piers. 

• Perform post-fire site evaluations for increased scour and erosion risks at bridges within 

the corridor (most importantly bridges rated as scour critical)
 

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• Identify the number of locations potential NRT gages would need to be installed to 

provide useful emergency response data. 

• Assist municipalities in assessing water supply facility capacities to address post-fire 

water quality and any needs for additional water quality monitoring. 

Future Study Efforts 

Creating an effective and efficient mechanism to implement, monitor, evaluate, and report on 

recovery activities, emergency responses, updates, and progress will require establishing staff 

roles, responsibilities, funding sources, and contact information across agencies. 

Corridor drainage structure data should be organized in a format that can be readily accessed 

and shared by multi-agency staff involved in the implementation. Data must also be 

geographically referenced, easily visualized, relevant, and up to date. Control of the data and 

necessary data sharing activities will need to be clearly defined. 

Once all hydrologic and hydraulic drainage data has been collected and relevant analysis has 

been performed, preventative mitigation measures will need to be identified and prioritized at 

all high-risk roadway drainage crossings and bridges. 

Throughout the vegetation recovery period, storm patrols will need to be conducted to monitor 

road drainage ditches, culverts, debris control structures, and bridges during and after 

significant rainfall events to ensure that structures remain safe and functioning at maximum 

capacity. A storm patrol plan and notification system will need to be developed and should be 

coordinated with other agencies accessing the corridor, including USFS, Clackamas County, 

Portland General Electric and ODOT. 

Agencies will also need to be establish an emergency maintenance plan. They should be 

prepared to provide significant maintenance efforts after storm events to remove sediment and 

debris from ditches and entrances to culverts. Addition removal of debris flow material from 

the roadway and repair of the roadway may also be needed. The emergency maintenance plan 

should address key components such as before, during, and post-storm activities, priorities, and 

responsibilities. The plan should identify staging, storage, disposal areas for heavy equipment, 

materials, and removed debris. 

cc: Sven Leon, WFLHD Senior Hydraulics Engineer 

Attachments: Appendix A - Maps
REFERENCES

Cerise, Luke, Mary Young. 2020. Soil Resource Report; Riverside Fire. Clackamas Ranger District, 

Mt. Hood National Forest

Cole, Ryan. 2021. Geotechnical Memo 30-21; Unstable Slope Data Gap Analysis. U.S. Department 

of Transportation; Western Federal Lands Highway Division. 

Clackamas River and Barlow Ranger Districts. 2020. Riverside and White River Fires Rapid 

Assessment Team Report. Mount Hood National Forest. 

Daggett, Anna, Kelsey Madsen, et al. 2020. Riverside Fire; Erosion Threat Assessment/Reduction 

Team (ETART) Summary Report. DR-4562-OR. Federal Emergency Management Agency

Huppi, Pete, Kevin Duchow. 2020. Mt Hood National Forest Burned Area Emergency Stabilization 

Plan; Riverside Fire; Engineering Resource Assessment – Transportation System. Mt. Hood National 

Forest.

Parker, Todd, Hazel Wood. 2020. Hydrology Report, Riverside Fire Burned Area Emergency 

Response. Mt. Hood National Forest. 

Staley, D.M, and J.W. Kean. 2020. Emergency assessment of post fire debris flow hazards, Riverside 

and White River Fires (Mt. Hood National Forest). U.S. Geological Survey 

U.S. Geological Survey. 2020. Clackamas River Basin Water-Quality Assessment. 

https://www.usgs.gov/centers/or-water/science/clackamas-river-basin-water-qualityassessment?qt-science_center_objects=0#qt-science_center_objects

U.S. Department of Agriculture Forest Service. 2020. Riverside and White River Fires Burned Area 

Emergency Response Geologic Hazards Assessment. 
 

APPENDIX A – MAPS
 

Riverside Fire - Basal Area Mortality Map
 

Riverside Fire – Soil Burn Severity Map 
 

Riverside Fire – Subwatershed Map 
 

Riverside Fire – Subwatershed Peak Stream Flow Analysis Points