IHSDM Technical Support

The Federal Highway Administration (FHWA) has discontinued IHSDM software 

development. However, FHWA will continue to provide free technical support via Geometric 

Design Laboratory (GDL) staff through at least September 2024, but essentially as long 

as agencies are still using the IHSDM 2021 (version 17.0.0) software.

Based on the current schedule, it is likely that the American Association of State 

Highway and Transportation Officials (AASHTO) will not publish the Highway Safety

Manual (HSM) second edition (HSM2) until at least 2024. Even after publication, 

agencies might need some time to transition from using HSM first edition (HSM1) 

methods/models to the new and/or recalibrated HSM2 models (e.g., to calibrate the new 

HSM2 models; to “vet” the new models for their use).(1) During that transition period 

(which will vary by agency), FHWA will continue to provide IHSDM/HSM support.

Since the HSM2 will include models for some facility types and/or crash types that 

differ significantly from the HSM1 form (e.g., new pedestrian and bicycle crash models), 

some parts of the IHSDM Crash Prediction Module (CPM) will become obsolete over 

time. At some point, the entire IHSDM CPM may become obsolete. Again, FHWA will 

provide IHSDM technical support to users until then.

FHWA’s IHSDM-Related Activities Beyond the 

2021 Release

Although FHWA will no longer carry out IHSDM software development, it will continue 

to provide the following:

• Free technical support via GDL staff through at least September 2024 (contact 

IHSDM technical support staff via email at IHSDM.Support@dot.gov or the Help Line 

at 202–493–3407). The FHWA Resource Center (RC) will also continue to provide 

IHSDM and HSM related technical assistance to agencies.

• Training sessions for IHSDM users via the FHWA RC (contact David Petrucci at 

david.petrucci@dot.gov) and the National Highway Institute (contact Thomas Elliott 

at thomas.elliott@dot.gov).

• IHSDM user group meetings and webinars, with a focus on agency applications 

and IHSDM case studies.

• Maintenance of the current FHWA IHSDM website (https://highways.dot.gov/

research/safety/interactive-highway-safety-design-model/interactive-highway-safetydesign-model-ihsdm-overview), which provides a means for users to download the 

IHSDM 2021 release and to obtain other information of interest.(9)

FHWA’s Future Plans for the Interactive 

Highway Safety Design Model (IHSDM)

For More Information

Visit https://bit.ly/IHSDM-Overview.
IHSDM 2021 (Version 17.0.0)—

CPM Capabilities

IHSDM version 17.0.0 (i.e., “IHSDM 2021”)—made 

available in September 2021—marked the end of FHWA’s 

IHSDM software development effort. Capabilities related 

to the CPM and the HSM are as follows:

• CPM includes implementation of HSM1 part C 

predictive methods for the following:

o Rural two-lane highways (HSM chapter 10).(1)

o Rural multilane highways (HSM chapter 11).(1)

o Urban/suburban arterials (five or fewer lanes)

(HSM chapter 12).(1)

o Freeway segments (HSM chapter 18).(1)

o Freeway ramps/interchange components

(HSM chapter 19).(1)

• CPM also includes the following predictive methods 

developed via the National Cooperative Highway 

Research Program (NCHRP) for inclusion in HSM2:

o Urban/suburban arterials (six or more lanes 

and one-way) (NCHRP 17-58).(2)

o Roundabouts (NCHRP 17-70).(3)

o Intersection types not in HSM1 (NCHRP 17-68).(4)

• CPM utilizes user-defined crash modification factors 

(UDCMF).

• IHSDM Economic Analyses Tool uses CPM evaluation 

results (crash frequency/severity).

• IHSDM Administration Tool includes a Calibration 

Utility/Tool to assist agencies in implementing the 

calibration procedures described in the appendix 

to HSM part C. Through the Administration Tool, 

users can also modify the crash distribution dataset 

and model dataset values (e.g., safety performance 

function (SPF) coefficients and exponents).

The following future HSM2 methods were not completed 

by the end of IHSDM software development in September 

2021 and so will not be implemented in IHSDM:

• Pedestrian and bicycle crashes (NCHRP 17-84).(5)

• Improved prediction models for crash types and 

crash severities (NCHRP 17-62).(6)

• Part-time shoulder use (PTSU) on freeways 

(NCHRP 17-89).(7)

• High-occupancy vehicle (HOV)/high-occupancy 

toll (HOT) lanes on freeways (NCHRP 17-89A).(8)

Future IHSDM Software Maintenance

Although the IHSDM software development contract has 

ended, FHWA/GDL will continue to provide certain types 

of software maintenance, such as the following:

• Track potential “bugs” in the IHSDM software; 

catalog and post information regarding known 

“bugs”—and workarounds (when applicable).

• Maintain a list of desired software enhancements 

users requested.

FHWA will also consider creating IHSDM configuration 

files to represent updates to existing HSM models, 

where possible (i.e., for updated HSM2 part C models 

that have the same structural form as HSM1 models). 

Through NCHRP 17-72(10) and 17-71A(11), some existing 

models will be “recalibrated” for HSM2 using single-state 

calibration. Existing IHSDM configuration files for HSM

default models can be updated to reflect the recalibrated 

models (changing coefficients and exponents). These 

configuration files may be made available to IHSDM/

HSM2 users via the IHSDM website. (Users can also 

do this on their own, but FHWA might provide the 

updated files to assist users/agencies.)

GDL may also provide updated configuration files for 

Economic Analysis Model Data Sets on an annual basis.
Future HSM-Related Activities

The GDL will continue to provide services related 

to HSM-related research and activities.

HSM-Related Research

The GDL’s significant experience with HSM methods, 

from both the research and practitioner perspectives, 

supports a host of potential HSM-related research 

activities. Main focus areas include the following:

• Quality of the HSM predictive method, which 

includes reviewing all HSM2 draft materials.

• Guidance in applying HSM part C methods.

• Identification of and response to gaps in HSM 

part C methods.

Other HSM-Related Activities

FHWA/GDL will continue to provide the following:

• Support to agencies as they seek to understand, 

apply, and implement the new HSM2 methods.

• Assistance to AASHTO in providing technical 

support to HSM users (including investigating 

potential errors in HSM1/HSM2) and to promote 

data-driven safety analysis through application 

of HSM methods. In some cases, this assistance 

might include support for using IHSDM to apply 

HSM part C methods.

FHWA/GDL can provide input on gaps/research needs 

for the future third edition HSM (e.g., identify gaps in 

the HSM2) and examine how the HSM fits with the Safe 

System Approach and the forthcoming AASHTO Green 

Book eighth edition.(12)

The AASHTO Committee on Safety and the Transportation 

Research Board (TRB) Safety Performance and Analysis 

Committee (ACS20) are collaborating on “restarting” an 

HSM User Discussion Forum. Although the future format 

and structure are unknown at this time, there is agreement 

that the discussions need to be moderated (e.g., to ensure 

that information shared on the forum is accurate). FHWA 

envisions a potential GDL role as one of the moderators 

of the restarted forum.

FHWA has shifted priorities away from IHSDM software 

development activities. However, technical support and 

knowledge transfer will still be provided for a range of 

IHSDM- and HSM-related activities well into the future.

For More Information, Contact:

In-Kyu Lim

FHWA, Office of Safety and Operations R&D 

6300 Georgetown Pike 

McLean, VA 22101

In-Kyu.Lim@dot.gov

202–493–3288

Jerry Roche

FHWA, Office of Safety 

105 6th Street

Ames, IA 50010

Jerry.Roche@dot.gov

515–233–7323

David Petrucci

FHWA, Resource Center

31 Hopkins Plaza, Suite 840

Baltimore, MD 21201

David.Petrucci@dot.gov

202–823–2260
FHWA-HRT-23-017 

HRSO-10/01-23(200)E

Federal Highway Administration, 

Interactive Highway Safety Design 

Model (IHSDM) (Washington, DC: 2023) 

https://doi.org/10.21949/1521960

References

1. AASHTO. 2010. Highway Safety Manual (First 

Edition). Washington, DC: AASHTO.

2. Lord, D., S. Geedipally, M. P. Pratt, E. S. Park, S. H. 

Khazraee, and K. Fitzpatrick. 2022. Safety Prediction 

Models for Six-Lane and One-Way Urban and 

Suburban Arterials. Washington, DC: The National 

Academies Press. https://doi.org/10.17226/26515, 

last accessed October 17, 2022.

3. Ferguson, E., J. Bonneson, L. Rodegerdts, N. Foster, B. 

Persaud, C. Lyon, and D. Rhoades. 2019. Development 

of Roundabout Crash Prediction Models and 

Methods. Washington, DC: The National Academies

Press. https://doi.org/10.17226/25360, last accessed 

October 17, 2022.

4. Torbic, D. J., D. J. Cook, K. M. Bauer, J. R. Grotheer, 

D. W. Harwood, I. B. Potts, R. J. Porter, J. P. Gooch, K. 

Kersavage, J. Medina, and J. Taylor. 2021. Intersection 

Crash Prediction Methods for the Highway Safety 

Manual. Washington, DC: The National Academies 

Press. https://doi.org/10.17226/26153, last accessed 

October 17, 2022.

5. TRB of the National Academies of Sciences, Engineering, 

and Math (NASEM). 2017. NCHRP 17-84, Pedestrian 

and Bicycle Safety Performance Functions for the 

Highway Safety Manual. Washington, DC: The 

National Academies Press. https://apps.trb.org/

cmsfeed/TRBNetProjectDisplay.asp?ProjectID=4203, 

last accessed October 17, 2022.

6. Ivan, J. N., S. Al Mamun, N. Ravishanker, B. Persaud, 

C. Lyon, R. Srinivasan, B. Lan, S. Smith, T. Saleem, 

M. Abdel-Aty, J. Lee, A. Farid, and J.-H. Wang. 2021. 

Improved Prediction Models for Crash Types and 

Crash Severities. Washington, DC: The National 

Academies Press. https://doi.org/10.17226/26164, 

last accessed October 17, 2022.

7. Jenior, P., J. Bonneson, L. Zhao, W. Kittelson, E. 

Donnell, and V. Gayah. 2021. Safety Performance 

of Part-Time Shoulder Use on Freeways, Volume

2: Conduct of Research Report. Washington, 

DC: The National Academies Press. https://doi.

org/10.17226/26393, last accessed October 17, 2022.

8. TRB of the NASEM. 2018. NCHRP 17-89A, HOV/

HOT Freeway Crash Prediction Method for the 

Highway Safety Manual. Washington, DC: The 

National Academies Press. https://apps.trb.org/

cmsfeed/TRBNetProjectDisplay.asp?ProjectID=4498, 

last accessed October 17, 2022.

9. Federal Highway Administration. 2022. “Interactive 

Highway Safety Design Model (IHSDM): Overview” 

(web page). https://highways.dot.gov/research/safety/

interactive-highway-safety-design-model/interactivehighway-safety-design-model-ihsdm-overview, last 

accessed October 17, 2022.

10. TRB of the NASEM. 2015. NCHRP 17-72 Update 

of Crash Modification Factors for the Highway 

Safety Manual. Washington, DC: The National 

Academies Press. https://apps.trb.org/cmsfeed/

TRBNetProjectDisplay.asp?ProjectID=3875, last 

accessed November 2, 2022.

11. TRB of the NASEM. 2021. NCHRP 17-71A Proposed 

AASHTO Highway Safety Manual, Second Edition. 

Washington, DC: The National Academies Press. 

https://apps.trb.org/cmsfeed/TRBNetProjectDisplay.

asp?ProjectID=5043, last accessed November 2, 2022.

12. AASHTO. Forthcoming. A Policy on Geometric 

Design of Highways and Streets. (Eighth Edition). 

Washington, DC: AASHTO.