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Seyedehsan (Ehsan) Dadvar, PhD, RSP1
NRC Fellow at FHWA
Lifesavers 2020 Conference
March 16th, 2020
Tampa, FL
How can the Highway Safety Manual
(HSM) and associated tools save lives?
Source: FHWA
Source: FHWASource: AASHTO
Workshop: Innovative Engineering to Protect All Road Users
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Outline
● Introduction
● Highway Safety Manual (HSM)○ Overview
○ Forthcoming 2nd Edition
● Interactive Highway Safety Design Model (IHSDM)○ Overview
○ Case Studies
● Crash Modification Factor (CMF) Clearinghouse○ Overview
○ New feature in IHSDM (Ver. 15.0.0): “User-defined CMFs”
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Road Safety in the US
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Road safety in the US (Cont.)
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NY-30A & NY-30, Schoharie, NY 12157
Schoharie Limousine Crash (October 6th, 2018)
The deadliest road crash since 2005
20 people killed:
● Driver and 17 passengers of a limousine
● Two pedestrians in parking lot
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Road Safety in the News
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Road Safety in Research
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Highway Safety Manual (HSM)
● The 1st edition published: 2010○ New chapters on freeways & ramps were released in 2014
● Methodology is like that for assessing and assuring
the adequacy of capacity
● HSM allows the transportation professionals to
understand and quantify highway safety performance
for informed and balanced decision making;
however, does not replace design manuals.
● “[T]he HSM is written for practitioners at the state,
county, metropolitan planning organization (MPO), or
local level (HSM, Page 1-1).”
7www.highwaysafetymanual.org
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(Cont.)
Objective
● Reduce the number / severity of crashes within the limits of available
resources, science, technology, and priorities
Application
● Identify facilities with the greatest potential for safety improvement
● Compare different design options
● Assess the safety “benefits” when conducting a B/C analysis
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Source: FHWA
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(Cont.)
Application: Same traffic volume, two alternatives vs. No-Build!
The HSM can be used in conjunction with Road Safety Audits (RSA).
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(Cont.)
HSM four parts:
● Part A — Introduction, Human Factors, and Fundamentals
● Part B — Roadway Safety Management Process
● Part C — Predictive Method
● Part D — Crash Modification Factors
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❖ Network Screening
❖ Diagnosis
❖ Select Countermeasures
❖ Economic Appraisal
❖ Prioritize Projects
❖ Safety Effectiveness Evaluation
CRSMS Tool for ConnDOT
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(Cont.)
HSM four parts:
● Part A — Introduction, Human Factors, and Fundamentals
● Part B — Roadway Safety Management Process
● Part C — Predictive Method
● Part D — Crash Modification Factors
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❖ Rural Two-lane Roads
❖ Rural Multi-lane Highways
❖ Urban / Suburban Arterial Highways
❖ Freeway Segments & Speed-Change Lanes
❖ Ramps, C-D Roads, & Ramp-Terminals
HSM Spreadsheet Tools
(including ISATe)
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(Cont.)
HSM four parts:
● Part A — Introduction, Human Factors, and Fundamentals
● Part B — Roadway Safety Management Process
● Part C — Predictive Method
● Part D — Crash Modification Factors
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421 CMFs
❖ Roadway Segments
❖ Intersections
❖ Interchanges
❖ Special Facilities and
Geometric Situations
❖ Road Networks
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(Cont.)
● Safety performance of different facility types investigated:○ Roadway segments, Intersections / Interchanges
○ Rural, Urban & Suburban
● Safety impact of different factors examined:○ Lighting
○ Horizontal Curvature (e.g., radius)
○ Lane Width
○ Automated Speed Enforcement
○ Median Width
○ Right / Left Shoulder Width
○ Left / Right Side Barrier
○ Driveways
○ Roadside Fixed Objects
○ etc.13
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(Cont.)
● The 2nd edition of the HSM is under development.
● Revised chapters and improved content (e.g., expanded human factors)
● More facility types:
○ More intersection types (e.g., roundabouts)
○ More roadway segment types (e.g., one-way highways)
● Improved approach of predicting crashes involving pedestrians / bicyclists
● Improved transfer / calibration approach to apply models to local conditions
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Interactive Highway Safety Design Model (IHSDM)
● A “free-of-charge” product of FHWA’s Safety Research and Development
Program: Geometric Design Laboratory (GDL)
● A suite of software tools that support project-level geometric design decisions
● Provides quantitative information on the expected safety and operational
performance
● IHSDM results help project developers make design decisions that improve
the expected safety performance
● IHSDM helps project planners, designers, and reviewers justify and defend
geometric design decisions (e.g., RSAs)
15www.ihsdm.org
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● Crash Prediction Module (CPM) ⇒ Faithful implementation of the HSM Part C
● Policy Review Module (PRM) ⇒ Faithful review of the AASHTO Green Book
● Design Consistency Module (DCM)
● Intersection Review Module (IRM)
● Traffic Analysis Module (TAM)
● Driver/Vehicle Module (DVM)
● Economic Analysis Tool
● Administration Tool (including Calibration utility)
(Cont.)
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IHS
DM
Mo
du
les
Substantive Safety
Nominal Safety
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(Cont.)
Pennsylvania: PA I-70 Yukon/Madison Interchanges
18Source: Michael Dimaiuta, Mohamad Banihashemi, Pennsylvania’s Use of IHSDM for a Safety Analysis of Freeway
Interchange Design Alternatives on I-70, TRB 2016
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(Cont.)
Maryland: Finding hot-spots on MD-100 using IHSDM
20Source: Seyedehsan Dadvar et al., Complexity vs. Predictability: Evaluation of Different Levels of HSM Predictive
Methods on Maryland Route 100, TRB 2017
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(Cont.)
Colorado: Ramp reconfiguration & restriping alternatives safety analysis using IHSDM
21Source: Michael Dimaiuta, Mohamad Banihashemi, Jacob Southard, Colorado I-225/I-25 Ramp Reconfiguration and
Restriping Alternatives: Safety Analysis Using IHSDM, TRB 2018
Existing
Note: Due to using uncalibrated models, numbers are valid
for alternative comparison only.
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(Cont.)
Minnesota: Connection safety analysis using IHSDM
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Source: Ellen Nightingale, Brandon Yarbrough, US-31 at I-94 Connection Alternative Analysis, TRB 2020
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(Cont.)
Wisconsin DOT Safety Certification Process Development
● Incorporating HSM & IHSDM in the process
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Source: Lee Gibbs, Identify Cost-Effective Safety-Driven Improvements for Roadways, TRB 2020
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(Cont.)
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Example of Economic Analysis on a freeway segment:
● 3.8 mile section
Base Case:
● Shoulders vary from 4 ft to 10 ft
● Lane widths vary from 10.6 ft to 13 ft
Alternative 1 ⇒ Widening all shoulders to 10 ft
Alternative 2 ⇒ Changing lane widths to 12 ft
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(Cont.)
Example of Economic Analysis on
a freeway segment (Cont.)
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Crash Modification Factor (CMF) Clearinghouse
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Source: FHWA Safety Data and Analysis: Application of CMFs
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(Cont.)
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Source: FHWA Safety Data and Analysis: Application of CMFs
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(Cont.)
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Source: FHWA Safety Data and Analysis: Application of CMFs
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(Cont.)
● The CMFs quantify the expected
changes in crashes compared to base
conditions due to given countermeasures
or existing conditions at applicable sites.
● The CMF Clearinghouse is a web-based,
comprehensive, and searchable
database of published CMFs:○ Illuminating an unlighted road segment
○ Paving gravel shoulders
○ Signalizing a stop-controlled intersection
○ Choosing a signal cycle time of 70 seconds
instead of 80 seconds
○ etc.29www.cmfclearinghouse.org
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(Cont.)
As of Feb. 10th, 2020:
● 1,203 countermeasures
● 8,310 CMFs○ 7,288 CMFs (star-rated)
○ 1,022 CMFs (non-star-rated)
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(Cont.)
Comparison table of
selected CMFs:
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(Cont.)
Top 20 countermeasures on CMF Clearinghouse by number of CMFs:
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(Cont.)
State Selected CMF Lists
● Help practitioners to
find appropriate CMFs
● Consistency in CMF
use across the state
35As of July 2019
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&
New feature in IHSDM (Ver. 15.0.0):
● The capability for users to define and apply “User-defined CMFs”
● The CMFs can be from CMF Clearinghouse and other sources
● The locally-developed CMFs can be used as well.
● Currently, “User-defined CMFs” can be entered by crash severity (FI, PDO, & Total)
36Example application: Curve radius CMF for multilane arterials
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Conclusions
The HSM / IHSDM / CMF Clearinghouse have broad applications:
● Identify sites with the most potential for crash reduction
● Recognize factors contributing to crashes
● Find associated countermeasures to address the issues
○ CMF Clearinghouse (more than 8,000 CMFs)
● Conduct economic appraisals of improvements and prioritize projects
● Assist practitioners in their RSAs
○ IHSDM can be a handy tool to compare alternatives and make informed decisions.
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FHWA Training
● National Highway Institute (NHI) Training
○ HSM Practitioner's Guide Courses (NHI 380070), (NHI 380070A), and (NHI 380070B)
○ Interactive Highway Safety Design Model (NHI 380071) & more
● Safety Data and Analysis Training videos
○ Predictive method, Observed, Expected Predicted Crashes
○ Application of CMFs, Selecting / Applying a Method to Analyze Multiple CMFs & more
● Resource Center Training
○ FHWA Practitioner’s Workshop for the Highway Safety Manual
○ FHWA HSM Roadway Safety Management Process & more
38https://safety.fhwa.dot.gov/rsdp/training.aspx
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Seyedehsan (Ehsan) Dadvar, Ph.D., RSP1
National Research Council (NRC) Research Associate
Geometric Design Laboratory (GDL)
Turner-Fairbank Highway Research Center (TFHRC)
Federal Highway Administration (FHWA)
[email protected]
(202) 493-3134
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