Roadway Safety Data Program

PENNSYLVANIA’S STATE-SPECIFIC SPFs AND CMFs 

ROADWAY SAFETY DATA AND ANALYSIS

CASE STUDY

FHWA-SA-16-062

Federal Highway Administration Office of Safety

Roadway Safety Data Program

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

November 16, 2016 
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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Notice 

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objective of the document.

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PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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TECHNICAL DOCUMENTATION PAGE

1. Report No.

FHWA-SA-16-062

2. Government Accession 

No.

3. Recipient's Catalog No.

4. Title and Subtitle

Pennsylvania’s State-Specific SPFs and CMFs: Roadway Safety Data and 

Analysis Case Study

5. Report Date

Month Year 

6. Performing Organization Code

7.Author(s) 

Robert A. Scopatz and Sarah Smith

8. Performing Organization Report No.

9. Performing Organization Name and Address

VHB

8300 Boone Blvd., Suite 700

Vienna, VA 22182-2626 

10. Work Unit No.

11. Contract or Grant No.

DTFH61-10-D-00022

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

Final November 2016

14. Sponsoring Agency Code

FHWA

15. Supplementary Notes

The contract manager for this report was Esther Strawder. 

16. Abstract

Pennsylvania Department of Transportation (PennDOT) used Part C of the Highway Safety Manual (HSM) to develop 

State-specific safety performance functions (SPFs). For some facility types, PennDOT calibrated the SPFs at the district or 

regional level within the State. PennDOT believes that pre-selecting applicable CMFS, and developing State-specific and 

regionally calibrated SPFs offers the best approach for addressing the State’s unique features and for dealing with the 

inherent differences among areas within the State. As the list of countermeasures in the CMF Clearinghouse continues to 

grow, practitioners can use the criteria to select from among the newly added CMFs.

17. Key Words: 

safety data, crash modification factor (CMF), 

safety performance function (SPF), safety 

management

18. Distribution Statement

No restrictions.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this 

page) Unclassified

21. No. of Pages

 12

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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TABLE OF CONTENTS

INTRODUCTION......................................................................................... 1

OBJECTIVE ................................................................................................... 3

AUDIENCE.................................................................................................... 3

DEVELOPING STATE-SPECIFIC SPFS .................................................... 3

COLLECTING THE DATA TO DEVELOP STATE-SPECIFIC SPFS .... 4

DEVELOPMENT OF STATE-SPECIFIC CMFS AND CMF “HOW TO” 

GUIDE............................................................................................................ 4

TRAINING COURSES ................................................................................. 5

RESULTS ....................................................................................................... 6

FUNDING ......................................................................................................................6

BENEFITS......................................................................................................................6

BARRIERS AND HOW THEY WERE OVERCOME.................................................7

LESSONS LEARNED....................................................................................................7

NEXT STEPS.................................................................................................................7

REFERENCES................................................................................................ 8

AGENCY CONTACT INFORMATION .................................................... 9
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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ACRONYMS

AASHTO American Association of State Highway and Transportation Officials

CMF Crash modification factor

FHWA Federal Highway Administration

HSM Highway Safety Manual

PennDOT Pennsylvania Department of Transportation

SPF Safety Performance Function

TRCC Traffic Records Coordinating Committee
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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EXECUTIVE SUMMARY 

The Pennsylvania Department of Transportation (PennDOT) used Part C of the Highway Safety 

Manual (HSM) to develop State-specific safety performance functions (SPFs). For some facility 

types, PennDOT developed district/regional-level calibrations of the State-specific SPFs. 

PennDOT developed regional SPFs and calibrated State-specific SPFs for use at the regional 

level. They believe this is the best approach for dealing with the inherent differences among 

areas within the State.

The PennDOT Highway Safety and Traffic Operations Division developed a guide on the 

appropriate use of State-specific crash modification factors (CMFs). This guide is based on a 

critical review of the CMFs available in the FHWA CMF Clearinghouse to identify CMFs 

applicable to Pennsylvania. PennDOT’s “Pennsylvania CMF Guide” includes information on 

these selection criteria as well as best practices to guide practitioners on how to use CMFs 

appropriately in various scenarios. As the list of countermeasures in the CMF Clearinghouse 

continues to grow, practitioners can use the criteria to select from among the newly added 

CMFs.
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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INTRODUCTION 

The American Association of State Highway and Transportation Officials (AASHTO) published

the 1st edition of the Highway Safety Manual (HSM) in 2010. The HSM describes the most upto-date analytic tools and techniques for quantifying the safety effects of decisions made in the 

planning, design, operations, and maintenance phases of project development. In particular, Part 

C of the HSM provides crash prediction models that States can use to predict potential safety

benefits of various design alternatives and engineering treatments. Part C also gives instruction 

on how to develop State-specific safety performance functions (SPFs) or calibrate the SPFs 

available in the HSM to a particular jurisdiction.

The Pennsylvania Department of Transportation (PennDOT) Highway Safety and Traffic 

Operations Division wrote a white paper to gain acceptance of the HSM. The paper explains 

the benefits of adopting the HSM, with a focus on using safety dollars more efficiently. 

BACKGROUND

The Highway Safety and Traffic Operations staff members developed a one-year deployment 

plan in which they proposed revising the Department’s design and procedure manuals to align 

with the HSM. Training sessions with relevant PennDOT staff members and business partners 

(FHWA, Turnpike, consultants, and local municipalities) took place throughout 2014 and 2015. 

During this time, the Highway Safety and Traffic Operations Division developed State-specific 

SPFs and crash modification factors (CMFs). There are 38,000 miles of State-maintained roads 

for which PennDOT has some attribute data and 78,000 miles of local roads for which the 

Agency has no attribute data. PennDOT judged that the majority of safety projects would be on 

rural two lane roads; however, the State lacked detailed data on local roadway segments and so 

decided to begin by creating State-specific SPFs for State-maintained two-lane rural roads. Over 

the course of the project, they developed State-specific SPFs for other facility types, as well as 

regional SPFs and calibration factors.

Additionally, the Highway Safety and Traffic Operations Division developed a guide on the 

appropriate use of State-specific CMFs. This guide is based on a critical review of the CMFs 

available in the FHWA CMF Clearinghouse (www.cmfclearinghouse.org) to identify CMFs 

applicable to Pennsylvania.
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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OBJECTIVES 

PennDOT developed State-specific SPFs in order to have SPFs based on State data rather than 

having to calibrate the models found in the HSM. This decision was based on an examination of 

the published SPFs and noting that they were not developed with Pennsylvania data. Attempts 

to calibrate the SPFs led to the realization that the published functions could be replaced with 

State-specific ones for about the same investment as calibration would have required. 

Ultimately, this effort led the State to recognize the need for regional calibration as well.

Agencies seeking guidance on whether to calibrate SPFs from the HSM or develop jurisdictionspecific SPFs can use the FHWA SPF Decision Guide to support this decision process at 

http://safety.fhwa.dot.gov/rsdp/downloads/spf_decision_guide_final.pdf.

There are a vast number of CMFs available in the CMF Clearinghouse, but PennDOT wanted to 

use only those that were most applicable to Pennsylvania, so they developed their own Statespecific CMF list. PennDOT also recognized the need to train staff on the importance of CMFs 

and how to use them appropriately. To this end, they developed the “how to” guide for using 

CMFs.

AUDIENCE 

The audience for this case study includes: 

 State Departments of Transportation: Safety Engineering, Design, Planning, Maintenance, 

Geographic Information System (GIS), and Asset Management Units.

 Local and Regional: City and County Public Works/Engineering/Transportation 

Departments, Metropolitan Planning Organizations, and Regional Planning Commissions.

 Local Technical Assistance Programs.

 Consultants and private industries involved with safety.

DEVELOPING STATE-SPECIFIC SPFs 

PennDOT started by developing statewide State-specific SPFs for rural two-lane roads. They 

found that the values of the statewide SPFs were not reliable for use across jurisdictions. Their 

solution, to develop regional SPFs, calibrates the State-specific SPFs for use at the regional level. 

They believe this is the best approach for dealing with the inherent differences among areas 

within the State.

As of January 2016, PennDOT, through contracts with Pennsylvania State University, has 

developed statewide State-specific SPFs as well as district-level and county-level calibration 
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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factors for rural two-lane and multilane roads, urban/suburban arterials, and 18 different 

intersection types. To develop district-level and county-level calibration factors, PennDOT 

selected one county in each district to use as a control county. On a district-wide basis, and for 

the remaining counties, they based the calibration factors on the control county. This 

procedure resulted in over 100 SPFs with each SPF having several calibration factors.

The original results of this effort gave PennDOT a complementary document to the HSM that 

is entirely Pennsylvania-specific. Additionally, PennDOT developed an Excel spreadsheet tool 

that includes the State-specific SPFs and CMFs, as well as the SPFs from the current HSM and a 

function for calculating benefit-cost ratios.

COLLECTING THE DATA TO DEVELOP STATE-SPECIFIC SPFs 

Developing State-specific SPFs for various segment facility types requires roadway data. 

PennDOT lacks some data elements for the State-maintained roads. Thus, they needed to 

collect all pertinent roadway data elements for the State-maintained roads that were not 

already included in the available databases. For example, the SPF for rural two-lane roads 

includes horizontal curve and grade data and roadside hazard rating as data elements. The preexisting PennDOT databases did not include these data elements. PennDOT undertook an 18-

month data collection effort for roughly 10,000 miles of rural two-lane roads, 6,000 miles of 

urban/suburban arterials, and 700 miles of rural multilane roads. The end product covers about 

20,000 miles of the 40,000 miles of State-maintained roadways.

There are also many data elements needed to develop the State-specific SPFs for various 

intersection facility types. PennDOT has a roadway management system that includes an 

intersection database of State-maintained intersections, but not local intersections. 

DEVELOPMENT OF STATE-SPECIFIC CMFs AND CMF “HOW TO” 

GUIDE 

The CMF Clearinghouse contains over 5,000 CMFs for various engineering countermeasures. In 

order to give Pennsylvania practitioners a way to easily navigate the CMF Clearinghouse, a team

of staff members critically reviewed each CMF in the Clearinghouse to determine if it was 

applicable to Pennsylvania. Criteria for inclusion in the State-specific CMF listing were:

 If a CMF used Pennsylvania data in its development, PennDOT included the CMF in the 

Pennsylvania list in lieu of other CMFs with similar characteristics developed in other 

States.
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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 If a CMF used no Pennsylvania data in its development, PennDOT used the star rating 

(quality of the CMF assigned by Clearinghouse reviewers) to determine if the CMF was 

included in the Pennsylvania list.

o If there was only one CMF with a 5-star rating for a particular countermeasure, 

they used that CMF.

o If there were several highly rated CMFs for a particular countermeasure, staff 

reviewed each report to determine which were most applicable to Pennsylvania.

o PennDOT reviewed only CMFs with at least a 3-star rating.

 PennDOT uses CMFs in the project development stage when there is not much detail 

known and therefore, more generalized countermeasures are more applicable. So, they 

selected only generalized countermeasures from the Clearinghouse (not too narrowly 

defined for specific roadway features or crash types).

 PennDOT selected only countermeasures with characteristics that apply to 

Pennsylvania. For example, if a particular countermeasure applies to roadways of a 

certain traffic volume that does not exist in Pennsylvania, PennDOT did not include the 

countermeasure. 

 PennDOT selected only studies without a lot of variability (large standard errors).

 PennDOT only included CMFs developed in the United States.

PennDOT’s “Pennsylvania CMF Guide” includes information on these selection criteria as well 

as best practices to guide practitioners on how to use CMFs appropriately in various scenarios. 

As the list of countermeasures in the CMF Clearinghouse continues to grow, practitioners can 

use the criteria to select from among the newly added CMFs as well. 

TRAINING COURSES 

To train staff on CMF use and interpretation, PennDOT ran lunchtime webinars sponsored by 

the American Society of Highway Engineers. Approximately 200 people (mostly consultants) 

attended the lunchtime webinars. 

PennDOT also sponsored PennDOT-specific HSM training classes, offered seven times between 

December 2014 through June 2015. The developers of the training class adapted material from 

NCHRP 17-38 Highway Safety Manual Implementation and Training Materials to make it specific to 

Penneslyvania. Approximately 200 people participated in the trainings. Of those, 140 were 

PennDOT employees (safety, traffic, and design personnel from Headquarters and the 

Districts), and the remaining were business partners (FHWA, Turnpike, consultants, and local 

municipalities). Content for the seven HSM training classes focused on two-lane rural road 

SPFs, CMFs, and a preliminary version of the Excel spreadsheet tool including crash prediction

and benefit-cost analysis, .
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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PennDOT intends to offer the PennDOT specific HSM training class nine more times by the 

end of December 2017. These additional classes will be broader in scope and will include 

information on design exceptions and alternatives analysis. The target audience is PennDOT 

district engineering staff, including design, safety, and traffic engineering professionals.

RESULTS 

The following sections describe the funding sources, benefits, barriers and how they were 

overcome, lessons learned, and next steps for the development of PennDOT’s state-specific 

SPFs and CMFs. From a PennDOT perspective, this was a valuable and necessary effort, as it 

gives them the information they need to make valid, reliable decisions and shows them how to 

best use the Federal publications and guidance.

FUNDING 

The funding for the State-specific SPF development came from the National Highway Traffic 

Safety Administration (NHTSA) traffic records (Section 405c) grant funds. The Traffic Records 

Coordinating Committee (TRCC) approved the project as part of the traffic records strategic 

plan and assisted PennDOT with the grant application. 

The cost of development and delivery of the initial seven HSM training classes was 

approximately $110,000. Of that, PennDOT spent $40,741 on training development, and the 

remainder covered delivery in the seven sessions.

The cost of State-specific SPF development was $950,000, including data collection, data 

analysis, draft and final reports, “Pennsylvania CMF Guide”, and the Excel spreadsheet tool. 

Specifically, SPF and CMF development was $696,000, and development of the Excel 

spreadsheet tool was $253,000.

PennDOT is aware that they may need to reinvest in this research every three to five years; 

however, at this time, they have no formal plans to do so.

BENEFITS 

PennDOT identified the following benefits of State-specific SPF and CMF development:

 After developing State-specific and regional SPFs and calibration factors for all desired

facility types in Pennsylvania, PennDOT has a document and a spreadsheet tool that are

entirely Pennsylvania specific.

 PennDOT plans to use the State-specific SPFs to aid in network screening in order to

select (for example) HSIP project locations. Rather than using just historical crash data
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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to identify HSIP project locations, they will be able to use State-specific SPFs that 

account for variables such as traffic volume and roadway classification.

 State-specific SPFs and CMFs will be useful in benefit-cost analyses. PennDOT has a 

publication that gives costs for specific items, and combining this document with the 

treatments derived from the selected State-specific CMFs will assist in estimating costs 

for projects. The State-specific SPFs and CMFs will provide more realistic estimated 

benefits for the benefit-cost ratio analysis because they are based on Pennsylvania data.

 More realistic benefit-cost ratio analyses could help with public education since 

PennDOT has more confidence in the numbers they present. It will be easier to 

illustrate to the public the benefits of engineering safety treatments.

BARRIERS AND HOW THEY WERE OVERCOME 

PennDOT is still trying to educate designers and engineers on the HSM. It is a tough transition 

for many who have over 20 years of experience using the AASHTO “A Policy on Geometric 

Design of Highways and Streets” (Green Book). The HSM gives the State more reliable 

estimates of safety benefits of various countermeasures. This helps them be more effective and 

efficient when identifying and addressing safety issues. PennDOT is trying to make sure the 

designers and engineers get the information early enough to have time to understand and 

implement the new methods successfully.

LESSONS LEARNED 

The State has determined that there is no one-size-fits-all approach to SPFs and CMFs.

PennDOT found it necessary to tailor the information to their State, and again to different 

regions within the State. The national studies and publications are usually based on a core 

sample, making it important to understand how similar a particular State—in this case 

Pennsylvania—is to the States participating in the study. If there are not enough similarities, 

decision-makers must make the decision whether to apply that national-level guidance or use 

their own data.

It may not be necessary or practical for all States to develop State-specific SPFs and/or CMFs. It 

is beneficial for States who are considering this effort to gather as much information as possible 

from other States who have already developed State-specific SPFs or CMFs to see if it is 

valuable for their State. Agencies can also use the FHWA SPF Decision Guide to support this 

decision process at http://safety.fhwa.dot.gov/rsdp/downloads/spf_decision_guide_final.pdf.

NEXT STEPS 

PennDOT will continue to train relevant staff on State-specific SPFs, “Pennsylvania CMF Guide”, 

and Excel spreadsheet tool.
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REFERENCES

The following resources were consulted in development of this case study:

1. PennDOT Highway Safety & Traffic Operations – Gary Modi. Telephone Interview. June 

10, 2015. 

2. PennDOT Highway Safety & Traffic Operations – Gavin Gray, Jason Hershock, and Eric 

Donnell. Telephone Interview. October 9, 2015.

3. PennDOT Highway Safety Manual Workshop. PowerPoint Presentation. December 8-9, 

2014. Riverfront Office Center. Harrisburg, PA.

4. Gayah, V.V., and E.T. Donnell. “Establishing Crash Modification Factors and Their Use 

(Pennsylvania CMF Guide)”. PennDOT Final Report. August 2014. 

5. Donnell, E., V. Gayah, and P. Jovanis. “Safety Performance Functions”. PennDOT Final 

Report. October 2014. Accessible at http://www.mautc.psu.edu/docs/PSU-2013-09.pdf.

6. Donnell, E., V. Gayah, and L. Li. “Regionalized Safety Performance Functions.” PennDOT 

Final Report. January 2016. Accessible at 

http://www.dot7.state.pa.us/BPR_PDF_FILES/Documents/Research/Complete%20Projects/

Operations/Regionalized_Safety_Performance.pdf.
PENNSYLVANIA’S STATE-SPECIFIC SPFS AND CMFS

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AGENCY CONTACT INFORMATION 

Gavin E. Gray, P.E.

Chief, Bureau of Maintenance and Operations

gagray@pa.gov

(717) 783-1190

Pennsylvania Department of Transportation

Highway Safety and Traffic Operations Division – Highway Safety Section

400 North Street, 6th Floor

Harrisburg, PA 17120

Jason P. Hershock

Manager, Safety Engineering & Risk Management – Bureau of Maintenance and Operations

jhershock@pa.gov

(717) 705-1437

Pennsylvania Department of Transportation

Highway Safety and Traffic Operations Division – Highway Safety Section

400 North Street, 6th Floor

Harrisburg, PA 17120

Eric T. Donnell, Ph.D., P.E.

Professor of Civil Engineering

edonnell@engr.psu.edu

(814) 863-7053

The Pennsylvania State University

231N Sackett Building

University Park, PA 16802