Alabama Department of Transportation

West South Boulevard 

Redesign Safety 

Assessment 

SAFETY DATA CASE STUDY 

FHWA-SA-21-075 

Federal Highway Administration Office of Safety 

Roadway Safety Data Program 

http://safety.fhwa.dot.gov/rsdp
i 

SAFETY DATA CASE STUDY FHWA-SA-21-075

Notice 

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SAFETY DATA CASE STUDY FHWA-SA-21-075

1. Report No.

FHWA-SA-21-075

2. Government Accession 

No.

3. Recipient's Catalog No.

 

4. Title and Subtitle

West South Boulevard Redesign Safety Assessment

5. Report Date

February 2022

6. Performing Organization Code

7.Author(s) 

Michael Dunn

8. Performing Organization Report No.

9. Performing Organization Name and Address

Vanasse Hangen Brustlin, Inc (VHB)

940 Main Campus Drive 

Raleigh, NC 27606 

10. Work Unit No.

11. Contract or Grant No.

DTFH61-16-D-00052

12. Sponsoring Agency Name and Address

Federal Highway Administration Office of Safety 

1200 New Jersey Ave., SE

Washington, DC 20590

13. Type of Report and Period

Case Study, January 2020-June 2022

14. Sponsoring Agency Code

FHWA

15. Supplementary Notes

The contract manager for this report was Jerry Roche. Funding for this effort provided in part by the Highway Safety 

Manual Implementation Pooled Fund, TPF-5(255). Sarah Weissman Pascual provided editorial review and support for 

technical content.

16. Abstract

This case study summarizes a safety analysis conducted by the Federal Highway Administration (FHWA) Geometric 

Design Lab (GDL), in collaboration with the Alabama Department of Transportation (ALDOT) and the FHWA Alabama 

Division. GDL used the Interactive Highway Safety Design Model (IHSDM) software to assess the safety performance of 

W South Boulevard, a high-volume, high-speed suburban arterial in Montgomery, Alabama. This analysis supported a 

proposed access management design that included pedestrian improvements. The existing corridor lacked pedestrian 

accommodations but exhibited notable pedestrian activity and informal worn paths. The corridor also experienced a higherthan-expected number of crashes in recent years, particularly pedestrian crashes. GDL used the IHSDM’s Crash Prediction 

Model to predict annual crashes and compare the existing condition of W South Boulevard with the proposed redesign that 

included pedestrian safety improvements. The results of the data-driven analysis informed ALDOT’s decision-making on 

the project and increased confidence in the pedestrian safety elements selected for the final design. W South Boulevard 

represents a facility type that is common throughout the United States, especially where suburban and rural areas interface 

and mixed land uses are adjacent to major freeway corridors. This example showcases one way that data-driven safety 

analysis and crash prediction available through IHSDM can enable agencies to make informed investments in road user 

safety.

17. Key Words: 

Suburban, Arterial, Pedestrian, Safety, IHSDM, 

Highway Safety Manual

18. Distribution Statement

No restrictions.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this 

page) Unclassified

21. No. of Pages

 20 

22. Price

Technical Documentation Page
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SAFETY DATA CASE STUDY FHWA-SA-21-075

Acronyms

Acronym Description

AADT annual average daily traffic

AASHTO American Association of State Highway and Transportation Officials 

ALDOT Alabama Department of Transportation

ATAP Alabama Transportation Assistance Program

CPM Crash Prediction Module

FHWA Federal Highway Administration

FI fatal and injury

GDL Geometric Design Laboratory

HSM Highway Safety Manual 

IHSDM Interactive Highway Safety Design Model

mph miles per hour

NCHRP National Cooperative Highway Research Program

PDO property damage only 

TWLTL two-way left-turn lane

vpd vehicles per day
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SAFETY DATA CASE STUDY FHWA-SA-21-075

Table of Contents

Introduction ................................................................................................................................... 1

Safety Performance Analysis ....................................................................................................... 4

Challenges ................................................................................................................................... 12

Conclusions ................................................................................................................................. 13

References................................................................................................................................... 14

List of Figures

Figure 1. Graphic. W South Boulevard project location. ......................................................... 1

Figure 2. Photo. Aerial photo of the prior condition of W South Boulevard between......... 2

Figure 3. Photo. Well-worn footpaths along the side of W South Boulevard........................ 3

Figure 4. Graphic. W South Boulevard as seen in the IHSDM Highway Viewer................... 6

Figure 5. Photo. Aerial photo of completed W South Boulevard improvements.............. 11

 

List of Tables

Table 1. W South Boulevard segment inputs for the existing scenario and proposed ......... 7

Table 2. W South Boulevard and Davenport Drive intersection inputs for the existing...... 9

Table 3. Predicted crashes per year for existing condition (2017 conditions). ................... 10

Table 4. Predicted crashes per year for proposed redesign (2017 conditions)................... 10

Table 5. Predicted pedestrian FI crashes per year (2017 conditions).................................. 11
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SAFETY DATA CASE STUDY FHWA-SA-21-075

Executive Summary

This case study summarizes a safety analysis conducted by the Federal Highway Administration 

(FHWA) Geometric Design Lab (GDL), in collaboration with the Alabama Department of 

Transportation (ALDOT) and the FHWA Alabama Division. GDL used the Interactive Highway Safety 

Design Model (IHSDM) software to assess the safety performance of W South Boulevard, a highvolume, high-speed suburban arterial in Montgomery, Alabama. This analysis supported a proposed 

access management design that included pedestrian improvements. The existing corridor lacked

pedestrian accommodations but exhibited notable pedestrian activity and informal worn paths. The 

corridor also experienced a higher-than-expected number of crashes in recent years, particularly 

pedestrian crashes. GDL used the IHSDM’s Crash Prediction Model to predict annual crashes and 

compare the existing condition of W South Boulevard with the proposed redesign that included 

pedestrian safety improvements. The results of the data-driven analysis informed ALDOT’s decisionmaking on the project and increased confidence in the pedestrian safety elements selected for the final 

design. W South Boulevard represents a facility type that is common throughout the United States, 

especially where suburban and rural areas interface and mixed land uses are adjacent to major freeway 

corridors. This example showcases one way that data-driven safety analysis and crash prediction 

available through IHSDM can enable agencies to make informed investments in road user safety.
1 

SAFETY DATA CASE STUDY FHWA-SA-21-075

Introduction 

The Transportation Research Board’s Safety Performance and Analysis (ACS20) User Liaison 

Subcommittee has an on-going initiative focused on practical application of the American 

Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual 

(HSM) (i.e., “using the HSM in the real world”). The Federal Highway Administration (FHWA) 

also administers the HSM Implementation Pooled Fund, which includes 22 States focused on 

projects to help further HSM implementation. Development of HSM case studies will assist 

practitioners in performing data-driven safety analysis using the advanced methods described in 

the HSM. The primary purpose of the HSM case studies is to highlight noteworthy applications 

of HSM methods, focus on common challenges, and feature agencies that overcame those 

challenges. These case studies serve as a source of lessons learned and noteworthy practices to 

help guide practitioners applying the HSM.

Background

This case study presents a collaboration between the FHWA Geometric Design Lab (GDL), 

FHWA Alabama Division, and the Alabama Department of Transportation (ALDOT). ALDOT 

identified W South Boulevard in Montgomery, Alabama as an opportunity to demonstrate how

a suburban arterial could be retrofitted to accommodate pedestrians and vulnerable users more 

safely. In support, GDL used the Interactive Highway Safety Design Model (IHSDM) software as 

part of the redesign process. Figure 1 shows the location and extent of the project.

© 2021 Google® © 2021 Maxar Technologies. Modified by the authors. 

Note: The white location pins and dashed line were added by the authors to delineate the project bounds.

Figure 1. Graphic. W South Boulevard project location.

 
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SAFETY DATA CASE STUDY FHWA-SA-21-075

Prior to the completed redesign in 2020, W South Boulevard between I-65 and Davenport 

Drive represented a common high-speed, high-volume arterial seen throughout the United 

States. W South Boulevard existed as an undivided suburban facility with three through lanes in 

each direction and a two-way left-turn lane (TWLTL), as shown in figure 2. It carried an annual 

average daily traffic (AADT) of 34,150 vehicles per day (vpd), with a posted speed limit of 50 

miles per hour (mph). The section that was the focus of this analysis is just over a half a mile in 

length, with a signalized diamond interchange on the west end at the intersection of W South 

Boulevard and I-65 and a four-leg signalized intersection on the east end at the intersection of 

W South Boulevard and Davenport Drive. On both ends of the corridor, the cross-section 

transitions from three through lanes in each direction to two. 

The corridor is primarily commercial, and contains several gas stations, hotels, fast food

restaurants, and other businesses. There are numerous driveways providing access between 

these businesses and W South Boulevard. There is a truck stop on the north side of W South 

Boulevard (as well as a Greyhound bus station that closed in 2019), and all of the restaurants 

are located on the south side of the road. This leads to many cases of pedestrians crossing the 

high-speed, high-volume seven-lane road at mid-block, uncontrolled locations. 

 

© ATAP 

Figure 2. Photo. Aerial photo of the prior condition of W South Boulevard between 

I-65 and Davenport Drive. 
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SAFETY DATA CASE STUDY FHWA-SA-21-075

Purpose and Need

The study area on W South Boulevard experienced a higher-than-expected number of crashes, 

particularly pedestrian crashes, over several years prior to a 2017 analysis. This prompted 

ALDOT to propose a redesign that included pedestrian accommodations. The existing segment 

did not include any notable pedestrian facilities, such as sidewalks or pedestrian countdown 

timers. In the absence of sidewalks, the pedestrian traffic had produced well-worn footpaths 

along both sides of W South Boulevard. Figure 3 shows the existing corridor, including the 

footpaths next to the roadway.

ALDOT reviewed the corridor’s crash history to diagnose the issues and identify potential 

treatments to address them. The proposed access management and pedestrian designs 

integrated several improvements along the length of the corridor including:

• Implementing a road diet on the westbound direction of W South Boulevard, reducing it

to two through lanes.

• Installing sidewalks along both sides of W South Boulevard.

• Installing a raised median with occasional left-turn pockets along the length of the

segment.

Figure 3. Photo. Well-worn footpaths along the side of W South Boulevard. 

 

© ATAP 
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SAFETY DATA CASE STUDY FHWA-SA-21-075

• Installing two high-visibility pedestrian crosswalks (one at a newly signalized intersection 

and one mid-block with a pedestrian-actuated traffic signal).

• Improving lighting along the corridor, specifically at the marked pedestrian crosswalks.

• Consolidating some driveway access points.

The FHWA GDL conducted an analysis and used the Crash Prediction Module (CPM) within 

IHSDM to assess the predicted safety performance of both the existing condition and proposed 

redesign. ALDOT then reviewed the safety performance of the two conditions and selected the 

proposed improvements.

Project Description

• Sponsoring agency: ALDOT. 

• Project location: Montgomery, AL. 

• Project bounds and length of project: W South Boulevard from I-65 to Davenport 

Drive (approximately 0.5 miles).

• Facility type(s): 7-lane, undivided major arterial.

• Area type: Suburban.

• Project status (as of October 2021): Analysis completed, and redesign constructed, 

incorporating the proposed design improvements. 

Safety Performance Analysis

This section provides an overview of the analysis methods, results, and the outcomes of the 

analysis. 

Analysis Overview 

The GDL used the IHSDM CPM to apply HSM Part C predictive methods to estimate the 

expected number of crashes for the W South Boulevard study corridor, including the 

interchange with I-65 on the west end and the intersection with Davenport Drive on the east 

end. The project team estimated expected crash counts for both the existing and proposed 

scenarios, to provide for a comparison. Comparing the design results to the existing results 

instead of the observed crash data was necessary because the models used in the CPM are not 

calibrated for use in Alabama. This is discussed in more detail in the Challenges section. 

HSM Part C (and subsequently IHSDM) models the different project components separately, 

meaning that the analysis involved the following elements:

• Highways: 

o W South Boulevard. 

o I-65. 

o Davenport Drive. 
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SAFETY DATA CASE STUDY FHWA-SA-21-075

• Interchange components: 

o I-65 northbound entrance ramp. 

o I-65 northbound exit ramp. 

o Ramp terminal (I-65 ramps and W South Boulevard). 

• Intersections: 

o W South Boulevard and Davenport Drive. 

The treatments addressed in the analysis included: 

• Changing the number of through lanes from six to five. 

• Addition of a raised median.

• Addition of a continuous, paved inside shoulder.

• Addition of lighting.

The analysts used the location-based method to enter data into IHSDM, allowing the segment 

to be viewed using the IHSDM Highway Viewer as shown in figure 4. The analysts estimated the 

horizontal alignment using aerial and streetview imagery to show an accurate representation of 

the geometry. 
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SAFETY DATA CASE STUDY FHWA-SA-21-075

Table 1 summarizes the model inputs for the W South Boulevard segment in both the existing 

and proposed scenarios. In the existing scenario, analysts estimated lane widths to be 12-ft for 

through lanes and 14-ft for the TWLTL using aerial imagery. The analysis included the TWLTL 

for the entire length of the corridor, except for short segments on both the west and east end 

where the median was either crosshatched or existed as a raised concrete median. A 2-ft paved 

outside shoulder was used along the entire length of the segment. A cumulative AADT of 

34,150 vpd combined both directions of travel based on previous data collection. The posted 

speed limit of 50 mph corresponded to the IHSDM speed category of “Intermediate/High.”

Figure 4. Graphic. W South Boulevard as seen in the IHSDM Highway Viewer. 

 

 

Source: FHWA

 

 

 

 
7 

SAFETY DATA CASE STUDY FHWA-SA-21-075

The analysis identified 33 driveways in total along the corridor. Two driveways in the 

westbound direction were categorized as “Major Industrial” and one in the eastbound direction 

was categorized “Major Commercial,” while the remainder were categorized as “Minor 

Commercial.” The density of fixed objects along the segment was set at 10 objects per mile and 

the offset was set at 20-ft, based on observations of Google MapsTM. 

For the proposed redesign, the number of through lanes in the westbound direction on W 

South Boulevard was reduced to 2, with 12-ft lane widths. The proposed design removed the

TWLTL, and a 2-ft paved inside shoulder was added in addition to the existing outside 

shoulder. The proposed design also consolidated one of the “Minor Commercial” driveways in 

the eastbound direction with other existing access points and added lighting along the entire 

length of the segment. All other inputs for W South Boulevard remained the same in both the 

existing and proposed redesign scenarios. 

Table 1. W South Boulevard segment inputs for the existing scenario and proposed 

redesign.

Item Existing Redesign

Number of thru lanes 6 5 

Divided vs. undivided Undivided Divided

Type and width of median TWLTL Raised; varies from 20 

ft to 24 ft

Presence of TWLTL Yes No

AADT 34,150 vpd - 

Traffic or posted speed range Intermediate/high 

speed - 

Left and right turn lanes

Left- and right-turn 

lanes at both 

intersection

Added left-turn lane 

into truck stop on EB

Roadside fixed object density Very low - 

Offset to fixed objects High - 

Average lane width 12 ft - 

Average outside shoulder width 2 ft - 

Density of railroad crossings 

(crossings/mi) 0 - 

Number of driveways 33 32 

Automated speed enforcement None - 

Presence of on-street parking None - 

Presence of lighting None Yes

Note: A cell with a “-“ indicates that the value for that item in the proposed redesign was the same as the 

value in the existing condition.
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SAFETY DATA CASE STUDY FHWA-SA-21-075

In addition to these data inputs for W South Boulevard, the analysis required certain data for I65, Davenport Drive, and the interchange and intersection between W South Boulevard and 

those two roads. The analysts used peak-hour volumes and a k-factor1 equal to 10 and 

computed the AADTs for the I-65 ramps and Davenport Drive. 

The analysts categorized the I-65 entrance and exit ramps as two-lane suburban ramps, with 

AADTs of 8,190 vpd and 5,060 vpd, respectively. The analysts classified the ramp terminal at W 

South Boulevard and I-65 as a four-leg ramp terminal (D4) with protected/permissive signal 

phasing for left turns and channelized right turns delineated with pavement markings. The only 

changes in the proposed ramp terminal configuration were a change in the number of lanes on 

the crossroad (W South Boulevard) and a change in the median width.

Table 2 summarizes the model inputs for the W South Boulevard and Davenport Drive 

intersection in both the existing and proposed scenarios. Davenport Drive was a two-lane 

suburban arterial, with an AADT of 2,630 vpd. The road’s speed was categorized as “Low” 

(given the posted speed limit of 25 mph). The intersection between W South Boulevard and 

Davenport Drive was a four-leg signalized intersection with three bus stops and one to eight 

alcohol sales establishments. The daily pedestrian volume across each approach was equal to 50 

pedestrians per day. The existing intersection had a maximum pedestrian crossing distance of 

seven lanes, included a protected left-turn signal phasing on W South Boulevard, and allowed 

right-turn-on-red with no channelization. The proposed intersection condition reduced the 

maximum lanes crossed by pedestrians from seven to four due to the addition of a median (i.e., 

pedestrian refuge). Proposed improvements also included the addition of lighting at the 

intersection.

1

 K-factor is the proportion of AADT occurring in the peak hour, otherwise known as the design hour volume 

(FHWA, 2018).
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SAFETY DATA CASE STUDY FHWA-SA-21-075

Table 2. W South Boulevard and Davenport Drive intersection inputs for the 

existing scenario and proposed redesign.

Item Existing Redesign

Number of legs 4 - 

Traffic control Signalized - 

AADT W South: 34,150 vpd

Davenport: 2,630 vpd

Number of lanes W South: 6/7

Davenport: 2/3 - 

Daily pedestrian volumes (sum crossing all 

legs)

Very low (under 

100/day) - 

Maximum number of lanes crossed by a 

pedestrian considering the presence of 

refuge islands

7 4 

Major road left-turn signal phasing Protected - 

Number of major road approaches with 

channelized right turn lane 0 - 

Number of approaches with right turn on 

red prohibited 0 - 

Number of approaches with U-turn 

prohibited 0 - 

Proportion of total crashes occurring at 

night Use default - 

Number of bus stops within 300 m 3 - 

School presence within 300 m 0 - 

Number of alcohol sales establishments 

within 300 m 1-8 - 

Presence of red-light camera None - 

Presence of lighting None Yes

Presence of left turn lane On both W South 

approaches - 

Presence of right turn lane On both W South 

approaches - 

Note: A cell with a “-“ indicates that the value for that item in the proposed redesign was the same as the 

value in the existing condition.

Crash Prediction Analysis & Results

The CPM analysis produced crash estimates for the year 2017. Table 3, table 4, and table 5

display these results for the existing condition, as well as the proposed redesign. The results in 

the tables correspond to the predicted number of crashes over the course of a year. Table 3

and table 4 show the predicted overall crash performance of the existing condition and 
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SAFETY DATA CASE STUDY FHWA-SA-21-075

proposed redesign, including fatal and injury (FI) crashes, property damage only (PDO) crashes, 

and total crashes. These two tables show that the proposed redesign for W South Boulevard

would be expected to reduce total crashes 21-percent annually, with a prediction of 39 crashes 

per year compared to the predicted 49 crashes per year in the existing condition. Within this 

total crash reduction, the proposed redesign predicted an 18-percent reduction in FI crashes 

(around 4 FI crashes per year) and a 24-percent reduction in PDO crashes (around 6 PDO 

crashes per year). 

Table 3. Predicted crashes per year for existing condition (2017 conditions). 

Analysis Component Facility Type FI 

Crashes

PDO 

Crashes

Total 

Crashes

W South Boulevard Suburban arterial 

segment 

3.90 6.22 10.13 

W South 

Boulevard/Davenport Drive

Signalized 4-leg 

intersection 2.40 2.91 5.31 

I-65 ramps/W South 

Boulevard Ramp terminal 15.82 17.88 33.70 

Total N/A 22.12 27.01 49.13

Table 4. Predicted crashes per year for proposed redesign (2017 conditions).

Analysis Component Facility Type FI 

Crashes

PDO 

Crashes

Total 

Crashes

W South Boulevard Suburban arterial 

segment 

2.17 3.96 6.14 

W South 

Boulevard/Davenport Drive

Signalized 4-leg 

intersection 2.03 3.41 5.44 

I-65 ramps/W South 

Boulevard Ramp terminal 14.01 13.25 27.26 

Total N/A 18.21 20.63 38.84

Based on the purpose and need of the project to improve pedestrian safety along the W South 

Boulevard corridor, table 5 focuses on predicted pedestrian crashes (which are all assumed to 

be FI crashes in the CPM due to pedestrian vulnerability). Note that the results in table 5 are 

included in the overall crash numbers seen in table 3 and table 4. While pedestrian crashes 

make up a smaller portion of the overall predicted crash numbers, these results still show an 

improvement of around 12 percent in pedestrian safety for the proposed design over the 

existing condition. Given the pedestrian crash history on W South Boulevard, this data-driven 

analysis demonstrated that the proposed design should help ALDOT meet the overall purpose 

and need of the project. 
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SAFETY DATA CASE STUDY FHWA-SA-21-075

Table 5. Predicted pedestrian FI crashes per year (2017 conditions). 

Analysis Component Facility Type

Pedestrian FI 

Crashes 

(Existing)

Pedestrian FI 

Crashes 

(Proposed)

W South Boulevard Suburban arterial 

segment 

0.13 0.105 

W South 

Boulevard/Davenport Drive

Signalized 4-leg 

intersection 0.15 0.14 

I-65 ramps/W South

Boulevard Ramp terminal 0.28 0.25 

Total N/A 0.56 0.495

Documentation and Use of Analysis Results

The FHWA GDL produced a brief report detailing the analysis inputs and results, including the 

data received from ALDOT describing the segment (FHWA, 2019). ALDOT used this report to 

finalize design decisions on the proposed improvements to W South Boulevard. 

The predicted decrease in total and pedestrian crashes per year increased ALDOT’s confidence 

in the proposed redesign, and ALDOT completed the project in 2020 (figure 5). The Alabama 

Transportation Assistance Program (ATAP) produced a set of before and after videos 

showcasing the project motivation and outcome (ATAP, 2019; ATAP, 2020).

Figure 5. Photo. Aerial photo of completed W South Boulevard improvements. 

© ATAP
12 

SAFETY DATA CASE STUDY FHWA-SA-21-075

Challenges

The HSM crash prediction models demonstrated that several design elements in the proposed 

redesign should reduce crashes compared to the existing condition, including decreasing the 

number of through lanes, adding a median, adding an inside shoulder, and adding lighting. 

However, it is important to note that several of the proposed improvements to W South 

Boulevard are not included in the HSM crash prediction models used in the IHSDM software. 

Excluded significant design features include the addition of sidewalks, pedestrian traffic signals, 

crosswalks and mid-block crossings, signage, and U-turn loons. In addition, the HSM models did

not account for the safety impact of restricted median crossings, restricting left turns to/from 

driveways, and frontage roads. 

One challenge for performing the analysis is that the proposed five-lane divided cross-section 

cannot be directly evaluated in IHSDM. However, the project team used a work around to 

mitigate this challenge. The project team conducted two evaluations, once as a four-lane divided 

road and once as a six-lane divided road. The final result for the proposed scenario was the 

average of the four-lane and six-lane results. It should be noted that the HSM (2010) does not 

include models for urban/suburban arterials with six or more lanes. However, National 

Cooperative Highway Research Program (NCHRP) Project 17-58 developed models for these 

facility types, and they are included in IHSDM (NCHRP, n.d.). Although the FHWA GDL did 

not take this approach, the project team noted that another possible approach would have 

been to model a four-lane divided road and apply a crash modification factor associated with 

adding a lane (especially for adding a fifth lane to a four-lane facility).

One specific challenge with interpreting the results of this analysis is that the models used in the 

CPM are not calibrated for use in Alabama. However, the project team tried to mitigate this 

challenge and designed the analysis to compare the existing condition with a proposed design. 

For facilities that use the same predictive model in both scenarios, such as the I-65/W South 

Boulevard ramp terminal and the W South Boulevard/Davenport Drive intersection, the 

relative difference between the two scenarios would still be valid even if calibration factors 

might have shifted the individual crash prediction results. Due to the more substantial changes 

to the W South Boulevard segment, the two scenarios depend on different predictive models. 

The potential calibration factors for these two models could vary, leading to possible 

differences in the estimated crash results.

ALDOT provided site-specific crash data for the segment, but they were not used in this 

analysis. While the HSM Part C methods include an Empirical-Bayes process to account for 

actual (observed) crashes, it is not applicable for projects in which the number of through lanes 

differs between scenarios. This project involved decreasing the number of through lanes from 

six in the existing condition to five in the proposed redesign. In addition, the facility type 

changed from undivided (with TWLTL) to divided. As a result, even though historic crash data 
13 

SAFETY DATA CASE STUDY FHWA-SA-21-075

were available, they were not used to predict future crashes for the existing and proposed 

designs. 

Conclusions

This example showcases a unique, but repeatable application of IHSDM to support pedestrian 

safety analysis and improve a high-volume, high-speed suburban arterials. ALDOT identified a 

specific need to improve pedestrian safety, and the FHWA GDL employed IHSDM to assess 

safety performance on the corridor and support ALDOT’s decision making and investments. 

Tables 4 and 5 show that the proposed improvements are expected to reduce total crashes, as 

well as FI pedestrian crashes on the corridor.

ALDOT specifically identified this portion of W South Boulevard for its pedestrian safety 

concerns. W South Boulevard represents a facility type that is common throughout the United 

States, especially where suburban and rural areas interface and mixed land uses are adjacent to 

major freeway corridors. ALDOT hopes this project can serve as a model for corridor 

redesigns in similar locations throughout the State. The safety analysis performed in support of 

this project provided confidence that these improvements can provide a repeatable framework 

to improve the pedestrian environment. 
14 

References

 AASHTO (2010). Highway Safety Manual: 1st Edition, Washington, D.C. Resources 

available online: http://www.highwaysafetymanual.org/Pages/default.aspx. 

ATAP (2019). Southern Boulevard Planned Pedestrian Safety Improvements [video]. 

https://www.youtube.com/watch?v=Fm5jPeCB3tM. 

ATAP (2020). Southern Boulevard Completed Safety Improvements [video]. 

https://www.youtube.com/watch?v=IyIUtXANNBA. 

 FHWA (2018). Traffic Data Computation Method Pocket Guide [FHWA-PL-18-027]. 

Available online: 

https://www.fhwa.dot.gov/policyinformation/pubs/pl18027_traffic_data_pocket_guide.pd

f

 FHWA (2021). “Interactive Highway Safety Design Model” (website). Available online: 

https://highways.dot.gov/research/safety/interactive-highway-safety-designmodel/interactive-highway-safety-design-model-ihsdm-overview.

FHWA (2019). West South Boulevard: Safety Analysis Report.

NCHRP (n.d.). Safety Prediction Models for Six-Lane and One-Way Urban and Suburban 

Arterials [NCHRP Project 17-58]. 

https://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3180

Contact

FHWA Geometric Design Lab

In-Kyu Lim, Manager

in-kyu.lim@dot.gov

ALDOT Design Bureau

John-Michael Walker, Traffic and Safety Operations Engineer

walkerjoh@dot.state.al.us