Michigan Department of Transportation

Michigan’s US 31 at I-94 

Interchange Alternatives 

Analysis 

SAFETY DATA CASE STUDY 

FHWA-SA-21-020 

Federal Highway Administration Office of Safety 

Roadway Safety Data Program 

http://safety.fhwa.dot.gov/rsdp
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SAFETY DATA CASE STUDY FHWA-SA-21-020

Notice 

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest 

of information exchange. The U.S. Government assumes no liability for the use of the information contained in 

this document. 

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names 

appear in this report only because they are considered essential to the objective of the document. 

Quality Assurance Statement 

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SAFETY DATA CASE STUDY FHWA-SA-21-020

1. Report No.

FHWA-SA-21-020

2. Government Accession 

No.

3. Recipient's Catalog No.

 

4. Title and Subtitle

Michigan’s US 31 at I-94 Interchange Alternatives Analysis

5. Report Date

September 2021

6. Performing Organization Code

7.Author(s) 

Ian Hamilton and Yuying Zhou

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-January 

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).

16. Abstract

Since 1981, the Michigan Department of Transportation (MDOT) has worked with the Federal Highway Administration to 

complete the US 31 freeway connection between I-80/90 in northern Indiana to I-94 in Berrien County, Michigan. The latest 

construction on the US 31 freeway ended in 2003 with a terminal interchange at Napier Avenue in Berrien County. The original 

US 31 alignment planned to connect the new freeway to the existing I-94 and I-196 interchange northeast of Benton Harbor, 

Michigan. However, MDOT identified a sensitive natural resource and endangered species habitat south of the I-94 and I-196 

interchange. Since this discovery, MDOT identified an acceptable tie-in at the I-94 and I-94 Business Loop partial interchange 

east of Benton Harbor. This case study presents MDOT’s iterative approach to project development that used the Interactive 

Highway Safety Design Model (IHSDM) software to identify a preferred design alternative based on a broad suite of traffic, 

safety, and cost considerations. The strategic application of IHSDM allowed MDOT to assess different design alternatives and 

project assumptions to make data-driven decisions for the proposed I-94 and US 31 interchange and surrounding network.

17. Key Words: 

Highway Safety Manual, HSM, Freeway, 

Interchange, Alternative

18. Distribution Statement

No restrictions.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this 

page) Unclassified

21. No. of Pages

 24 

22. Price

Technical Documentation Page
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SAFETY DATA CASE STUDY FHWA-SA-21-020

Acronyms

Acronym Description

AADT annual average daily traffic

AASHTO American Association of State Highway and Transportation Officials

CMF crash modification factor

EIS Environmental Impact Statement

FHWA Federal Highway Administration 

HSM Highway Safety Manual

IACR Interchange Access Change Request

IHSDM Interactive Highway Safety Design Model

MDOT Michigan Department of Transportation

LOS level of service

SPF safety performance function

TCAT Traffic Crash Analysis Tool

TIA Transportation Improvement Association

TOA Traffic Operations Analysis

TWCLTL two-way center left turn lane
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SAFETY DATA CASE STUDY FHWA-SA-21-020

Table of Contents

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

Safety Performance Analysis ................................................................................................................... 3

Conclusions and Lessons Learned ......................................................................................................... 17

References ................................................................................................................................................ 17

List of Figures 

Figure 1. Graphic. I-94/US 31 project location....................................................................................... 2

Figure 2. Graphic. Safety analysis project extents. ................................................................................ 4

Figure 3. Graphic. Build alternative 1. .................................................................................................... 7

Figure 4. Graphic. Build alternative 2. .................................................................................................... 8

Figure 5. Graphic. Build alternative 3. .................................................................................................... 9

Figure 6. Graphic. Build alternative 6. .................................................................................................. 10

Figure 7. Graphic. Modified alternative 2 and the final preferred alternative. ................................. 12

Figure 8. Graphic. Final proposed Build alternative design changes.................................................. 13

List of Tables

Table 1. Summary of project area crash history by facility type and severity. ................................... 5

Table 2. Summary of project area crash history by facility type and crash type................................ 5

Table 3. Summary of alternatives analysis findings. ............................................................................ 11

Table 4. Predicted crashes per year on I-94. ........................................................................................ 11

Table 5. Predicted crashes per year – no-build and build alternative................................................ 14

Table 6. Revised predicted crashes per year – no-build and build alternative. ................................. 17
 

SAFETY DATA CASE STUDY FHWA-SA-21-020

Executive Summary

Since 1981, the Michigan Department of Transportation (MDOT) has worked with the Federal Highway 

Administration to complete the US 31 freeway connection between I-80/90 in northern Indiana to I-94 in 

Berrien County, Michigan. The latest construction on the US 31 freeway ended in 2003 with a terminal 

interchange at Napier Avenue in Berrien County. The original US 31 alignment planned to connect the new 

freeway to the existing I-94 and I-196 interchange northeast of Benton Harbor, Michigan. However, MDOT 

identified a sensitive natural resource and endangered species habitat south of the I-94 and I-196 interchange. 

Since this discovery, MDOT identified an acceptable tie-in at the I-94 and I-94 Business Loop partial interchange 

east of Benton Harbor. This case study presents MDOT’s iterative approach to project development that used 

the Interactive Highway Safety Design Model (IHSDM) software to identify a preferred design alternative based 

on a broad suite of traffic, safety, and cost considerations. The strategic application of IHSDM allowed MDOT to

assess different design alternatives and project assumptions to make data-driven decisions for the proposed I-94 

and US 31 interchange and surrounding network.
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SAFETY DATA CASE STUDY FHWA-SA-21-020

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) 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 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

Since 1981, the Michigan Department of Transportation (MDOT) has worked with FHWA to complete 

the US 31 freeway connection between I-80/90 in northern Indiana to I-94 in Berrien County, Michigan. 

The latest construction on the US 31 freeway ended in 2003 with a terminal interchange at Napier 

Avenue in Berrien County (figure 1). The original US 31 alignment planned to connect the new freeway 

to the existing I-94 and I-196 interchange northeast of Benton Harbor, Michigan. However, MDOT 

identified a sensitive natural resource and endangered species habitat south of the I-94 and I-196 

interchange (the Blue Creek Fen). Since this discovery, MDOT identified an acceptable tie-in at the I-94 

and I-94 Business Loop (I-94BL) partial interchange east of Benton Harbor (HNTB, 2020a). This case 

study presents an interchange alternatives analysis and subsequent safety evaluation performed by 

MDOT as a part of the much larger US 31 extension and realignment project. 

MDOT plans to connect US 31 between Napier Avenue and I-94. MDOT will build a new interchange at 

the existing I-94 and I-94BL connection that accommodates US 31 and allows free-flow movements for 

major system-to-system ramps. As part of this freeway extension, MDOT and its consultant, HNTBTM, 

prepared a mobility report that considered the operational impacts of a substantial conversion of the 

existing interchange to four interchange Build alternatives:

1) Full cloverleaf.

2) Partial cloverleaf with three loops.

3) Partial cloverleaf with a loop.

4) Partial cloverleaf with two loops.

Once MDOT had a preferred interchange alternative design, the agency conducted a safety and mobility 

evaluation of the affected local network and developed a formal Interchange Access Change Request 

(IACR) document for FHWA’s consideration.
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SAFETY DATA CASE STUDY FHWA-SA-21-020

Purpose and Need

The US 31/I-94 interchange analysis, as well as the broader US 31 realignment project, focused on four 

primary needs (HNTB, 2020a): 

1) Improve mobility along the US 31 corridor with freeway system linkage to I-94. 

2) Enhance local access along I-94BL. 

3) Provide system-to-system connectivity along US 31 to relieve traffic congestion on Napier Ave, 

and improve access from I-94 to downtown Benton Harbor.

4) Minimize surrounding environmental impacts in light of current regional needs and traffic 

projections.

Figure 1. Graphic. I-94/US 31 project location.

© 2021 Google® Source: 2021 National Oceanic and Atmospheric Administration. Modified by the authors. 

Note: The white location pins, annotation text, and white dashed line were added by the authors to delineate the project bounds.
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SAFETY DATA CASE STUDY FHWA-SA-21-020

Project Description

• Sponsoring agency: MDOT.

• Project location: Benton Harbor, Berrien County, Michigan. 

• Project bounds and length of project: In addition to the I-94/I-94BL interchange, the overall 

FHWA-approved project study area included the following locations:

 I-94 from Britain Avenue to I-196. 

 The I-196/I-94 interchange and ramps. 

 The I-94/I-94BL interchange and ramps. 

 The I-94/Napier Avenue interchange, including ramps and ramp terminals on Napier 

Avenue. 

 The US 31/Napier Avenue interchange, including ramps and ramp terminals on Napier 

Avenue. 

 The I-196/Red Arrow interchange, including ramps but not the ramp terminals.

 The I-94BL between I-94 and Urbandale Avenue, including Euclid and Crystal avenues. 

• Facility type(s): 6-lane divided freeway (I-94), 4-lane divided freeway (I-94BL and US 31), and 

arterial roads.

• Area type: Urban.

• Project status (spring 2021): Under construction. 

Safety Performance Analysis

This section provides an overview of the existing safety conditions for the US 31 extension project, the 

interchange alternatives assessment findings, and the predictive analysis that compared the preferred 

Build alternative to the “No Build” option. MDOT’s approach considered a broad impact on the local 

network as part of the US 31 extension. Through this iterative process, MDOT made strategic changes 

to the final design to develop safety improvements at key locations in the project design. 

Existing Safety Conditions

This section provides an overview of MDOT’s analysis of existing safety conditions. This assessment of 

historic crash trends informed the alternatives analysis, as well as the trade-offs that produced the final 

design.

Study Area

MDOT developed a study area that incorporated a broad view of the overall US 31 extension project. 

This analysis included interchanges along I-94, US 31, I-196, and I-94BL, as well as bidirectional mainline 

segments on I-94, US 31, I-94BL, and Napier Avenue (figure 2).
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SAFETY DATA CASE STUDY FHWA-SA-21-020

Figure 2. Graphic. Safety analysis project extents.

© 2021 Google® Source: 2021 National Oceanic and Atmospheric Administration. Modified by the authors. 

Note: The white lines were added by the authors to delineate the project bounds.
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SAFETY DATA CASE STUDY FHWA-SA-21-020

MDOT analyzed historic crashes within the study area to evaluate existing traffic safety concerns and 

identify potential mitigation measures for critical safety issues. MDOT obtained crash data for a five-year 

period between 2014 and 2018 from the Transportation Improvement Association’s (TIA) Traffic Crash 

Analysis Tool (TCAT). The TIA is independent from MDOT, but it assists the State with transportation 

safety data, research, and education. Tables 1 and 2 summarize the crash history for freeway mainline 

and arterial segments, as well as ramps within the project study area (HNTB, 2019b). 

Table 1. Summary of project area crash history by facility type and severity.

Crash Severity Freeway Mainline 

Segments 

Arterial 

Segments Ramps

Fatal 4 0 0 

Serious Injury 10 2 2 

Minor Injury 16 8 8 

Possible Injury 52 32 16

Property Damage Only 601 136 122

Total 683 178 148 

Table 2. Summary of project area crash history by facility type and crash type.

Crash Type Freeway Mainline 

Segments 

Arterial 

Segments Ramps

Single Vehicle 455 31 82

Sideswipe - Same Direction 119 24 19

Rear-End 86 40 33

Other 12 0 6 

Angle 10 51 7 

Head-On 1 1 0 

Head-On Left Turn 0 13 0 

Rear-End Left Turn 0 1 0 

Rear-End Right Turn 0 5 0 

Sideswipe – Opposite Direction 0 7 1 

Backing 0 5 0 

Total 683 178 148 
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SAFETY DATA CASE STUDY FHWA-SA-21-020

To supplement traditional crash summaries, MDOT conducted site visits and drove the corridor to 

identify more qualitative observations of the study area. Based on the existing conditions analysis, 

MDOT developed the following recommendations for future interchange and mainline corridor designs: 

 Provide additional paved shoulder width to allow more room for vehicles to recover from a loss 

of control.

 Improve drainage to prevent water from collecting in travel lanes during inclement weather.

 Install lighting along I-94BL corridor.

 Install chevrons with flashers and other signage intended to reduce speed at interchange ramps.

 Provide standard acceleration and deceleration lengths to all ramps.

Interchange Alternatives Assessment

Before identifying a final alternative to compare against a potential No-Build scenario, MDOT prepared 

five conceptual designs for a future interchange between US 31 and I-94. The project team refined these 

conceptual designs with qualitative assessments and engineering judgment into four final practical 

alternatives: three alternatives from the original five (alternatives 1, 2, and 3) and an additional 

alternative developed during the collaborative discussion process (alternative 6). MDOT conducted a 

series of quantitative analyses that included a Peak Period Traffic Operations Analysis (TOA) to 

determine the effects of each alternative on traffic congestion and a predictive crash analysis using the 

Interactive Highway Safety Design Model (IHSDM) software. Through this combination of traffic and 

safety modeling, the MDOT project team iterated through a series of design tradeoffs associated with 

each alternative to arrive at a final, preferred alternative. Figures 3, 4, 5, and 6 provide an illustration and 

the following sections provide a general summary of each practical interchange alternative.
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SAFETY DATA CASE STUDY FHWA-SA-21-020

Build Alternative 1 (PA-1) was the recommended alternative selected in a 2004 Environmental 

Impact Statement (EIS). This full cloverleaf interchange would provide free-flow access for all 

movements with one-lane ramps (figure 3). No stop-controlled movements would be required in the 

interchange. Weaving would be required along US 31 and I-94 for traffic entering and exiting the ramps

(HNTB, 2020b). MDOT’s analysis of this alternative noted the following advantages and disadvantages

(HNTB, 2019a, p. 18). 

Advantages

 All movements would be free flow. 

 Relatively higher speed movements. 

 Minimized traffic conflict points. 

 Lowest number of expected crashes along US 31 and I-94BL.

Disadvantages

 Two bridges within I-94/US 31 interchange. 

 Highest construction cost. 

 Highest potential for county drain realignment. 

 Highest impervious pavement area with greatest detention required. 

 Largest footprint with no opportunity for excess right-of-way.

Figure 3. Graphic. Build alternative 1.

© 2021 Google® Source: 2021 National Oceanic and Atmospheric Administration. Modified by the authors. 

Note: The white lines and route shields were added by the authors to project design and extents.
8 

SAFETY DATA CASE STUDY FHWA-SA-21-020

Build Alternative 2 (PA-2) was a partial cloverleaf layout with loop ramps in two quadrants (figure 

4). All movements would free-flow off of the ramps, except for the ramps from NB US 31 and SB US 31 

which would require a left-turn from US 31. No access for the movement from EB I-94 to SB US 31 

would be permitted. No weave sections would be required in this alternative on either I-94 or US 31 

(HNTB, 2020b). MDOT’s analysis of this alternative noted the following advantages and disadvantages

(HNTB, 2019a, p. 20). 

Advantages

 Provided free flow movements between NB/SB US 31 and I-196. 

 One bridge within I-94/US 31 interchange. 

 No weaving between loop ramps within interchange. 

 Reduced potential for required county drain realignment. 

 Reduced impervious pavement area with potential for reduced detention. 

 Reduced construction cost (compared to PA-1). 

 Lower number of expected crashes along I-94 compared to PA-1. 

Disadvantages

 Not all movements within I-94/US 31 interchange would be free flow. 

 Introduced traffic conflict points at ramp terminals on US 31 and I-94BL. 

 Higher travel times between US 31 and I-196 compared to PA-1. 

 No I-94 EB to US 31 SB movement would be provided.

Figure 4. Graphic. Build alternative 2.

© 2021 Google® Source: 2021 National Oceanic and Atmospheric Administration. Modified by the authors. 

Note: The white lines and route shields were added by the authors to project design and extents.
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SAFETY DATA CASE STUDY FHWA-SA-21-020

Build Alternative 3 (PA-3) was another partial cloverleaf configuration, with only one loop ramp and 

more directional ramps compared to PA-2; this created two intersections in the interchange (figure 5). 

US 31 would be converted to an undivided roadway prior to the interchange, requiring one four-lane 

bridge over I-94. This alternative would remove the ramps from SB US 31 to EB I-94, NB US 31 to WB 

I-94, and EB I-94 to WB US 31. Left-turning movements would accommodate these movements at the 

ramp terminals. No weave sections would be required along either I-94 or US 31 (HNTB, 2020b).

MDOT’s analysis of this alternative noted the following advantages and disadvantages (HNTB, 2019a, p. 

22). 

Advantages

 Provided free flow movements between NB/SB US 31 and I-196. 

 No weaving between loop ramps within the interchange. 

 Reduced potential for required county drain realignment. 

 Reduced impervious pavement area with potential for reduced detention. 

 Reduced construction cost (compared to PA-1). 

Disadvantages 

 Not all movements within I-94/US 31 interchange are free flow. 

 Introduced traffic conflict points at ramp terminals on US 31 and I-94BL. 

 Higher travel times between US 31 and I-196 compared to PA-1. 

Figure 5. Graphic. Build alternative 3.

© 2021 Google® Source: 2021 National Oceanic and Atmospheric Administration. Modified by the authors. 

Note: The white lines and route shields were added by the authors to project design and extents.
10

SAFETY DATA CASE STUDY FHWA-SA-21-020

Build Alternative 6 (PA-6) utilized a partial cloverleaf as well. This was a hybrid design between PA-1 

east of I-94 and PA-2 west of I-94 (figure 6). All movements would be accommodated in this interchange 

design with most movements being free flow. The elimination of the loop ramp in the northwest 

quadrant allowed the outer connection ramp to be tightened and compressed the interchange footprint. 

The elimination of this loop ramp also removed the unbalanced weave WB on I-94 presented in PA-1 

(HNTB, 2020b). MDOT’s analysis of this alternative noted the following advantages and disadvantages 

(HNTB, 2019a, p. 24). 

Advantages

 Provided free flow movements between NB/SB US 31 and I-196. 

 Eliminated weaving between loop ramps along NB US 31/I-94BL and WB I-94. 

 Minimized traffic conflict points. 

 Lowered travel times between US 31 and I-196. 

Disadvantages 

 Two bridges within I-94/US 31 interchange. 

 Introduced traffic conflict points at west ramp terminals for US 31 NB to I-94 WB movement. 

 Higher construction costs.

 Higher impervious pavement area with greater detention required. 

 Larger footprint with less opportunity for excess right-of-way as compared to PA-2 and PA-3. 

 Higher number of expected crashes along I-94 as compared to PA-2 and PA-3.

Figure 6. Graphic. Build alternative 6.

© 2021 Google® Source: 2021 National Oceanic and Atmospheric Administration. Modified by the authors. 

Note: The white lines and route shields were added by the authors to project design and extents.
11

SAFETY DATA CASE STUDY FHWA-SA-21-020

The traffic analysis used VissimTM traffic simulation software. Table 3 summarizes the relevant findings 

from the alternatives analysis (HNTB, 2019a, p. 27). 

Table 3. Summary of alternatives analysis findings.

Criteria PA-1 PA-2 PA-3 PA-6 

Impervious Area (square feet) 4,975,000 4,607,000 4,566,000 4,809,000

Total Cost (all segments) $131,005,000 $119,958,000 $121,542,000 $127,016,000

Minimize impacts to the surrounding 

environment Acceptable Good Good Good/ Acceptable

Reduce construction costs from those 

estimated for the 1981 EIS alignment Acceptable Good Good Good/ Acceptable

Improve the efficiency of north-south 

vehicular travel and the movement of 

goods and services throughout the 

entire US 31 corridor

Good Good Good Good 

Improve local access within Berrien 

County Good Good Good Good 

Provide free-flow system connectivity 

through a north-south US 31 freeway 

linkage to the I-94 freeway

Good Good Good Good 

System-to-system connectivity and 

linkage Good Good/ Acceptable Good Good 

Relief of traffic congestion on Napier 

Avenue Good Good Good Good 

Improved access to I-94 and I-94BL to 

assist economic development Good Good Good Good 

Free-flow movement for traffic to 

access I-94, I-196, US 31 north, I-94BL 

from the existing US 31 freeway

Good Acceptable Acceptable Good/ 

Acceptable

The weekday AM and PM peak period models showed that all Build alternatives have a level of service

between A to C in the future year (2041). For safety comparisons, MDOT used IHSDM to predict 

crashes along I-94 based on each of the four alternatives. For example, Table 4 shows that PA-2 and PA3 had the lowest annual predicted crashes on I-94.

Table 4. Predicted crashes per year on I-94. 

Crash Severity PA-1 PA-2 PA-3 PA-6 

Total Crashes 41.83 39.57 39.56 40.95

Fatal and Injury Crashes 13.34 12.69 12.68 13.12

Property Damage Only Crashes 28.48 26.89 26.88 27.82
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SAFETY DATA CASE STUDY FHWA-SA-21-020

Based on the cumulative safety, operational, and environmental impact results, MDOT developed an 

additional alternative to improve the expected safety performance of the most promising design. The 

new alternative functionally matched the operational movements from PA-2, so no additional traffic 

analysis, safety analysis, or cost calculations were performed. Small modifications to PA-2 allowed the 

MDOT project team to address small concerns within the overall design to derive the final preferred 

alternative (e.g., incorporating painted gores to separate traffic at ramp conflicts). Figure 7 illustrates the 

final preferred alternative used in MDOT’s IACR analysis.

Predictive Analysis

MDOT used the HSM default safety performance functions (SPFs) in IHSDM to conduct a predictive 

crash analysis to compare the future year (2041) Build and No-Build alternatives. IHSDM uses roadway 

characteristics and traffic volumes to predict crashes based on the methods outlined in the HSM. 

The final proposed Build alternative addressed the project purpose and need by enhancing mobility and 

addressing environmental concerns (e.g., the Blue Creek Fen). Figure 8 illustrates the location of several 

design changes within the analysis study area:

Figure 7. Graphic. Modified alternative 2 and the final preferred alternative.

© 2021 Google® Source: 2021 National Oceanic and Atmospheric Administration. Modified by the authors. 

Note: The white lines and route shields were added by the authors to project design and extents.
13

SAFETY DATA CASE STUDY FHWA-SA-21-020

1. Extend US 31 north of Napier Ave to I-94.

2. Rebuild the existing interchange at I-94 and I-94 BL to accommodate US 31, I-94, and I-94BL. 

3. Resize I-94BL from a four-lane divided highway to a three-lane road, including a two-way center 

left turn lane (TWCLTL).

4. Add an auxiliary lane along the I-94 EB corridor between the proposed US 31 interchange and 

the existing I-196 interchange.

5. Reconstruct the I-196 ramps along the existing ramp alignments.

The Peak Period TOA and VissimTM output provided the traffic estimates for both alternatives. This 

showed substantial differences that would have a direct impact on anticipated safety performance. For 

instance, MDOT expected daily traffic volumes on I-94BL to nearly double as a result of the new US 31 

connection. Much of this traffic would be diverted from Napier Avenue and I-94 south of the new US 31

interchange in the Build alternative (thereby reducing traffic at these locations). However, the 

comparison of roadway geometry between both alternatives provided a more complex challenge. The 

Figure 8. Graphic. Final proposed Build alternative design changes. 

© 2021 Google® Source: 2021 National Oceanic and Atmospheric Administration. Modified by the authors. 

Note: The white dashed lines, pins, and circles were added by the authors to project extents.
14

SAFETY DATA CASE STUDY FHWA-SA-21-020

Build alternative, which included an extension of US 31 between Napier Avenue and I-94, contained 

substantial design differences that included approximately 3 miles of new freeway segments and 2.17 

miles of ramps (a 35-percent increase in road mileage). 

The Build design also called for the conversion of a two-way stop-controlled intersection at I-94BL and 

Crystal Avenue to a single-lane roundabout, as well as the conversion of the bridge at Euclid Avenue and 

I-94BL (that currently does not allow access between Euclid Avenue and I-94BL) to an at-grade, twoway stop-controlled intersection. To account for crash prediction differences between a two-way stopcontrolled intersection and a single-lane roundabout, MDOT applied a crash modification factor (CMF) 

of 0.7511 to the predicted crash results at the Crystal Avenue intersection (CMF Clearinghouse ID 

#4930). This reduced the total predicted number of crashes (all severities) at the intersection by 24.89 

percent.

Initial Results

MDOT submitted an initial round of crash prediction results to FHWA as part of an IACR in February 

2020. Table 5 summarizes these results.

Table 5. Predicted crashes per year – no-build and build alternative. 

Model Total Crashes Fatal and Injury 

Crashes 

Property 

Damage Only

No-Build Alternative 130.17 45.55 84.70

Build Alternative 131.07 45.74 85.32

Difference 0.90 0.19 0.65 

Percent Change 0.69% 0.41% 0.77% 

This analysis predicted a narrow, less than one-percent increase in crashes per year based on the Build 

alternative design. Although the project team expected the substantial increase in lane mileage and traffic 

to lead to a slight increase in crashes in most locations, the complete project study area contained 

locations for potential offsetting crash reductions:

 Reduced crashes on Napier Avenue as a result of redirected (i.e., reduced) traffic.

 Slight crash reductions through ramp and ramp terminal redesigns.

 Crash reductions as a result of the conversion of the Crystal Avenue and I-94BL at-grade 

diamond interchange to a roundabout. 

As a result of this slight increase, MDOT and FHWA worked to refine the Build alternative design, the 

IHSDM analysis methodology, and the application of relevant CMFs. Based on these discussions, the 

MDOT project team noted several challenges and changes to the project approach in a subsequent 

memorandum to FHWA in May 2020 (MDOT and HNTB, 2020). 

IHSDM Analysis Challenges

Prior to making changes to the crash prediction analysis, the MDOT project team noted the following 

limitations with respect to IHSDM or analysis assumptions:
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SAFETY DATA CASE STUDY FHWA-SA-21-020

 The project team had to make tradeoffs with respect adding a TWCLTL to I-94BL in IHSDM. 

The original design of I-94BL was functionally a freeway; however, IHSDM would not return 

crash prediction results with a TWCLTL located on a freeway. The project team could have 

classified the road as an arterial to obtain predicted crashes, but the team believed the character 

of the road (i.e., a two-lane suburban highway) was more in line with a freeway than an arterial. 

This likely over-estimated crashes in the Build alternative (i.e., a simple two-lane suburban 

highway) relative to what would be expected under the three-lane cross-section that includes a 

TWCLTL.

 Prior to the release of IHSDM version 15.0, it was not possible to model a roundabout for an 

intersection. MDOT submitted its IACR before this version was available, so the project team 

developed a scenario for the proposed conversion at Crystal Avenue that applied a CMF 

(#4930) to the existing two-way stop control to represent the conversion to a roundabout.

 The No-Build (i.e., existing) design of the Crystal Avenue and I-94BL intersection is an at-grade 

diamond interchange with all turn movements accommodated by ramps. Since IHSDM does not 

allow for an at-grade intersection between a freeway and arterial, the project team did not 

model this intersection in the No-Build scenario.

Updates to Build Design

The MDOT project team made two fundamental changes to the design after the initial IACR submittal:

1. The Build alternative no longer considered an at-grade intersection at Euclid Avenue and I-94BL; 

it would remain an overpass.

2. The Build alternative removed a portion of the proposed TWCLTL from Crystal Avenue and 

the I-94 WB off ramp; however, the Build alternative still considered a TWCLTL between 

Urbandale Avenue and Crystal Avenue.

Updates to Build Volumes

Based on the removal of the proposed at-grade intersection at Euclid Avenue and I-94BL, the project 

team adjusted future Build alternative traffic volumes to show traffic being re-routed to Crystal 

Avenue/I-94BL. 

Updates to the Predictive Crash Analysis

The MDOT project team made several adjustments to the revised predicted crash analysis based on the 

following changes and assumptions:

No-Build Alternative

 Since IHSDM does not allow for an at-grade intersection between a freeway and arterial to be 

modeled with the overall interchange, MDOT modeled the at-grade intersection separately 

from the overall project and added the results to the overall results for the Crystal Avenue/I94BL interchange. The project team accomplished this by modeling the ramps without 

connecting them to the cross-street in the primary model. Outside of the main model, the 

project team created the cross-street (Crystal Avenue) and created ramp terminals to model 

this aspect of the intersection. This allowed the project team to append ramp terminal results to 

the overall model results from the primary model.
16

SAFETY DATA CASE STUDY FHWA-SA-21-020

Build Alternative

 The MDOT project team replaced the original CMF for the conversion of a two-way stopcontrolled intersection to a roundabout and applied two separate CMFs instead:

1. A 0.348 CMF (65.2-percent reduction) for all fatal and injury crashes (CMF 

Clearinghouse ID #4935).

2. A 0.955 CMF (4.5-percent reduction) for all crashes (CMF Clearinghouse ID #4934).

This approach more accurately reflected the anticipated changes to fatal and injury crashes 

relative to total crashes. The project team determined the count of property damage only

crashes based on the percentage of fatal and injury and total crashes at the intersection.

 MDOT applied a new CMF to reflect the addition of a TWCLTL on a suburban highway. Rather 

than modeling a TWCLTL directly in IHSDM, the project team applied a CMF for installing 

TWCLTLs (CMF Clearinghouse ID #2341) that estimated a 20.3-percent reduction in all crash 

types for the section of I-94BL that would still receive the treatment (i.e., between Urbandale 

Avenue and Crystal Avenue).

 MDOT removed the proposed at-grade intersection at Euclid Avenue and I-94BL and 

redistributed traffic to the proposed Crystal Avenue roundabout.

Revised Results

Based on the aforementioned revisions to the Build and No-Build designs and crash prediction analysis, 

the MDOT project team reduced the number of predicted crashes per year in the Build alternative 

relative to the No-Build design (table 6). Although the revised Build design is expected to reduce total 

crashes by 5 per year, and fatal and injury crashes by 2 per year, over an anticipated future No-Build 

scenario, the project team noted that not all locations are expected to experience fewer crashes as a 

result of the project. For instance, the improved connectivity between US 31 and I-94BL in any Build 

scenario should increase traffic volumes on I-94BL. As a result, even though the improvements on US 

31, I-94, and I-94BL should reduce crashes as a whole, MDOT expected crashes on I-94BL alone to 

increase. Still, MDOT’s iterative approach that refined certain design elements, such as the proposed 

roundabout and TWCLTL on I-94BL, produced a project design that accommodates mobility needs 

while also reducing predicted crashes. 
17

SAFETY DATA CASE STUDY FHWA-SA-21-020

Table 6. Revised predicted crashes per year – no-build and build alternative.

Model

Total 

Crashes

(Original)

Fatal and 

Injury 

Crashes

(Original)

Property 

Damage 

Only

(Original)

Total 

Crashes

(Revised)

Fatal and 

Injury 

Crashes

(Revised)

Property 

Damage 

Only

(Revised)

No-Build Alternative 130.17 45.55 84.70 133.55 46.81 86.83

Build Alternative 131.07 45.74 85.32 128.24 44.42 83.98

Difference 0.90 0.19 0.65 -5.30 -2.39 -2.86

Percent Change 0.69% 0.41% 0.77% -3.97% -5.11% -3.29%

Conclusions and Lessons Learned

Although mobility and regional connectivity were the primary purpose and need of the US 31 extension, 

MDOT’s data-driven approach helped refine the final design of a complex project. A preliminary 

evaluation of recent crash history and site visits identified location-specific opportunities for safety 

improvement (e.g., installation of lighting, application of low-cost countermeasures, and provision of 

additional paved shoulder). IHSDM analysis allowed the project team to assess the safety performance of 

major design decisions and compare predicted safety outcomes with anticipated project benefits (tables 

3 and 4). This comparison led to the refinement of the original PA-2 interchange design into the final 

preferred alternative. Subsequent design revisions across the entire project footprint, based on IHSDM

analysis, also led to an alternative that anticipated fewer crashes relative to a No Build scenario (e.g., the 

removal of the at-grade intersection at Euclid Avenue and I-94BL, as well as the shortening of the 

TWCLTL on I-94BL).

Through MDOT’s iterative process, the project team also noted several key lessons for analyzing a large 

and intricate project with significant network impacts:

 Managing expectations is critical. It is important to be clear about the effectiveness and 

usefulness of modeling in the decision-making process. There are limitations to what can be 

modeled, as well as to the efficiency of making large changes to a complex model.

 Identify when and how modeling will be used early in the process. Complex safety 

modeling is an effective method for differentiating clear alternatives. Practitioners and decisionmakers should evaluate slight differences in potential alternatives according to preliminary 

screening criteria and engineering judgment before considering rigorous safety modeling. 

 IHSDM should be used strategically. Practitioners cannot do everything in IHSDM, and it is 

important to establish a clear strategy for using IHSDM. Users should apply IHSDM and safety 

modeling at stages in a project where it can add the most benefit to the decision-making process 

(i.e., once the project team had defined its preferred alternative designs).
18

References

 American Association of State Highway and Transportation Officials. (2010). Highway Safety 

Manual: 1st Edition, Washington, D.C.

 American Association of State Highway and Transportation Officials. (2014). Highway Safety 

Manual: 1st Edition, Supplement, Washington, D.C.

 Federal Highway Administration. (2021a). “CMF Clearinghouse” (website). Available online: 

http://www.cmfclearinghouse.org/index.cfm. 

 Federal Highway Administration. (2021b). “Interactive Highway Safety Design Model” 

(website). Available online: https://highways.dot.gov/research/safety/interactive-highway-safetydesign-model/interactive-highway-safety-design-model-ihsdm-overview.

 HNTB Corporation. (2019a). I-94/US-31 Alternatives Assessment Technical Memorandum, 

Kalamazoo, MI. 

 HNTB Corporation. (2019b). I-94/US-31 Traffic Safety Report, Kalamazoo, MI.

 HNTB Corporation. (2020a). I-94/US-31Interchange Access Change Request, Kalamazoo, MI. 

 HNTB Corporation. (2020b). I-94/US-31 Vissim Methods, Calibration, and Analysis Technical 

Memorandum, Kalamazoo, MI. 

 Michigan Department of Transportation and HNTB Corporation. (2020). I-94 at US-31 IACR 

Safety Analysis Update, memorandum to FHWA, Kalamazoo, MI. 

Contact

Michigan Department of Transportation

Dharmesh Valsadia, Innovative Contracting Project Manager

ValsadiaD@michigan.gov