IHSDM 2015 Overview

8/18/2019 IHSDM 2015 Overview

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Interactive Highway

Safety Design Model

(IHSDM)

September 2015


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What is the intent of the safety analysis for

a transportation improvement project?

o h e lp m ake

m o re in fo rm ed

pro jec t des ign

dec i s i ons

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Integrating Safety Analysis in Design


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The safety analysis should helpguide design decisions in effort to:

•

Mitigate existing risk features thatpotentially contribute to increasednumber and severity of crashes

• Reduce future safety risks bymaking effective and efficientdesign choices

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Good design is more than just looking up values “in the book”

It’s applying engineering knowledge of the relationship between

design factors and the “ safety performance” of the facility.


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IHSDM:

A Quantitative Approach to

Evaluating Highway Safety


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What is IHSDM?

• A suite of software tools that supportproject-level geometric design

decisions by providing quantitativeinformation on the expected safety andoperational performance

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What Benefits does IHSDM Provide?

• IHSDM results help project developersmake design decisions that improve the

expected safety performance of designs

• IHSDM helps project planners, designers,and reviewers justify and defend

geometric design decisions

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•As a tool to identify facilities where the “safetyperformance” is worse than expected

•Assists in making decisions where to investlimited resources in ways that will clearly improvesafety performance

Potential IHSDM Applications

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“… evolution in safety analysis fromdescriptive methods to quantitative,

predictive analysis” AASHTO Highway Safety Manual – Chapter 1 Introduction and Overview


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• As a tool to assess the safety “benefit” whenconducting a B/C analysis

- Predict crashes before and afterreconstructing or improving a facility


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•As a tool to assess design options:- Evaluate alternatives- Evaluate proposed design exceptions

- Evaluate and refine preliminary geometry


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• Enables more informed decision-making

• Helps explain decisions to stakeholders

IHSDM: A Quantitative Approach

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IHSDM

Evaluation

Module

Relationship to HSM

Crash Prediction Faithful implementation of HSMPart C Predictive Method

Policy Review Evaluates nominal safety; use in

conjunction with – not in place of –HSM Part C methods

DesignConsistency

Diagnostic tools that can supportHSM Part C evaluations

Traffic Analysis

IntersectionReview

Driver/Vehicle 12


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What Highway Types can

IHSDM Evaluate?

• Facility types:

– Two-lane rural highways (All Modules)

– Multilane rural highways (Crash Prediction &Policy Review)

– Urban & suburban arterials (Crash Prediction)

– Freeway segments (Crash Prediction)

– Freeway ramps/interchanges (Crash Prediction)

• Existing and proposed alternative highwaygeometric designs

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Data Needs

• Vary by IHSDM evaluation module (and byhighway type in CPM)

• Highway Segment Data (all modules)

• Intersection Data (CPM, IRM)

• Interchange Data (CPM)

• Crash Data (CPM - optional)

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IHSDM

Evaluation

Module

Relationship to HSM




DesignConsistency


Traffic Analysis

IntersectionReview

Driver/Vehicle 15


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Crash Prediction Module (CPM)

Typical Uses

Predicts crash frequency for highway

segments, intersections and interchanges

Evaluates the safety impact of highwayimprovements/treatments

Compares relative safety performance of

design alternatives

Assesses safety cost effectiveness of

design decisions

Crash

Prediction

Module

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Relationship between

IHSDM CPM and the HSM

A. Introduction and Fundamentals

B. Roadway Safety Management Process

C. Predictive Method (IHSDM CPM)

Chapter 10: Rural, Two-Lane Roads

Chapter 11: Rural, Multilane Highways

Chapter 12: Urban & Suburban Arterials

Chapter 18: Freeways

Chapter 19: Ramps

D. Crash Modification Factors

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Estimating Expected Crashes

•Model components for crash prediction:

• Safety Performance Functions (SPFs)

(i.e., “base models”)•Crash Modification Factors (CMFs)

•Calibration Factors

•

Site-specific crash history (Empirical-Bayes process)

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2014 Supplement to the HSM

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Predictive Method for:

• Freeways

• Ramps


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CPM for Freeway Segments

and Ramps/Interchanges

• Implements methods described inHSM 2014 Supplement, including theCalibration procedure

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CPM for Freeways / Ramps

Capabilities

• Evaluation of freeway segments,including segments with speed

change lanes• Evaluation of freeway ramps/

interchanges, including:

– Ramps– Collector-Distributor (C-D) Roads

– Ramp Terminals

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CPM for Freeways/Ramps

Capabilities

• CPM automatically segments highways forevaluation (including freeway segments,

ramps and C-D roads), following HSMChapters 18/19

• Application of the Empirical-Bayes (EB)

process to factor in historical crash data -for freeway segments, ramps, C-D roadsand ramp terminals

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CPM Data Needs

• Highway Segment Data

• Intersection Data

•

Crash Data (optional)

CPM data needs vary by highway type:

• Rural 2-lane Highways (2R)

• Multilane Rural Highways (MR)

• Urban/Suburban Arterials (U/SA)

• Freeways (F)

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HSM Roadway Segmentation

= IHSDM Roadway Segmentation

From HSM Ch. 10, p. 10-11:

For all HSM Part C chapters:

“ The definit ions of roadway segments and intersections…

are the same as those used in the FHWA IHSDM.”


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Site-Specific Crash Data

(Empirical-Bayes Process)

• Improves accuracy of estimates for a particular highway.

• Captures effects of many factors not in model or CMFs.

• Has a synergistic effect when combined with a model

estimate of producing data that is more accurate than either

component could produce alone.

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CPM Output

• Highway data

• Evaluation Report

– Crash frequency and rate

– Crash type distribution• Graphs

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CPM

Calibration Utility

• Assists agencies in implementing thecalibration procedures described in theAppendix to HSM Part C

– Organizes Required and Desired Data

– Calculates Calibration Factors

• Allows agencies to enter their own SPFsand to modify default crash distributions

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Why use IHSDM to implement

HSM Part C Methods?

• Can evaluate many highwaysegments, intersections andinterchanges over a number of years

• “Station-Based” Data Inputautomatically segments the highwayinto homogeneous segments as per

HSM Part C• “Site-Based” Data Input – especially

useful for projects where detailed,station-based geometry not available

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HSM Part C Methods?

• Can handle complex (and simple)alignments

•

Seamlessly evaluates a highway thatchanges facility type (e.g., rural 2-lane to rural multilane)

• Implements the Empirical-Bayes

procedure

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HSM Part C Methods?

• IHSDM “Navigation tree” helps usersto organize projects, highways,evaluations, etc.

• Evaluation Reports and Graphsprovide extensive documentation ofresults / output

• Highway Viewer provides graphicalrepresentation of design

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HSM Part C Methods?

• Extensive documentation in “HelpBrowser”

• Tutorial provides step-by-step “soupto nuts” guidance

• IHSDM Administration Tool includesa Calibration Utility to help agencies

implement HSM CalibrationProcedures

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Other IHSDM Evaluation

Modules

• IHSDM Evaluation • Module

• Relationship to HSM

• Crash Prediction• Faithful implementation of HSM Part C Predictive Method• Policy Review• Evaluates nominal safety; use in conjunction with – not in place

of – HSM Part C methods• Design Consistency

• Diagnostic tools that can support HSM Part C evaluations• Traffic Analysis• Intersection Review• Driver/Vehicle

IHSDM

Evaluation

Module

Relationship to HSM




DesignConsistency


Traffic Analysis

IntersectionReview

Driver/Vehicle32


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Policy Review Module

Scope

•Checks roadway segmentgeometry against relevant

design policy and “flags”variations

•Applies to rural 2-lane and

rural multilane highways

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Policy Check Categories

•Cross-Section

•Horizontal Alignment

• Vertical Alignment

• Sight Distance

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Stopping Sight Distance Graphs

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Other IHSDM Evaluation

Modules

• IHSDM Evaluation • Module

• Relationship to HSM

• Crash Prediction• Faithful implementation of HSM Part C Predictive Method• Policy Review• Evaluates nominal safety; use in conjunction with – not in place

of – HSM Part C methods• Design Consistency

• Diagnostic tools that can support HSM Part C evaluations• Traffic Analysis• Intersection Review• Driver/Vehicle

IHSDM

Evaluation

Module

Relationship to HSM




DesignConsistency


Traffic Analysis

IntersectionReview

Driver/Vehicle36


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Design Consistency Module

Scope

• Estimates 85thpercentile speed profile

along alignment toevaluate operatingspeed consistency

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Design Consistency Module

Estimated Operating Speed Profile

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Traffic Analysis Module

Scope

• Traffic simulation model

• Estimates traffic quality of servicemeasures (mean speeds; % following)

•Helps evaluate climbing and passinglane alternatives, volume, and capacity

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Traffic Analysis Module

Mean Speed and Following

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Intersection Review Module

Scope

• Expert system that applies rules ofgood practice in a comprehensive

diagnostic review of a singleintersection

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Identifies possible safety concernsand typical treatments

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Intersection Review Module

Evaluation Report

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Driver/Vehicle Module

Scope

• Simulates driving behavior andvehicle dynamics on a two-lane

highway

• Provides profiles of predictedspeed and other response

variables, via a simulation of asingle driver/vehiclecombination

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Driver Vehicle Module

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IHSDM Workflow

1. Create a project

2. Establish highways, intersections, and

interchanges; input data

3. Run evaluation module(s)

4. View results (output)

Synthesize IHSDM Output

Establish project goals

I

H

S

D

M

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IIHSDM User Interfacee

Desktop

Operations

Panel

Message

Box

Menu Bar

Navigation

Tree

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Data Input Options

Data Input

Export data from

design software into

LandXML format and

then import into IHSDM

Copy and paste

data from a

spreadsheet

Add data via the IHSDM Highway Editor,

Intersection Editor or Ramp Terminal

Editor; or via the IHSDM Site Set Editor


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Typical IHSDM Applications

• Evaluate relative safety impacts ofalternative designs for EIS (CPM+)

• Evaluate expected safety impacts of

recently completed improvements (CPM+)• Safety analysis of preliminary construction

plans (CPM+)

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Evaluate operational impacts of passing/climbing lanes (TAM)

• In conjunction with Road Safety Audits(CPM, DCM, IRM, PRM)

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Typical IHSDM Applications

• Quantify relative safety/operationalperformance of alternatives and compareagainst other (e.g., environmental, cost)

impacts (CPM, TAM+)• Refine alternatives to optimize safety and

operational performance (All)

• Evaluate / prioritize 3R safetyimprovements (All)

• Verify design exception areas (PRM, CPM)

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2015 Release

• Download: http://www.ihsdm.org

• Technical support:– [email protected]

– (202)-493-3407

• Training:– On-Site: FHWA-NHI-380071

– Web-based: FHWA-NHI-380100

– See NHI catalog at http://nhi.fhwa.dot.gov

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http://www.ihsdm.org/mailto:[email protected]://nhi.fhwa.dot.gov/http://nhi.fhwa.dot.gov/mailto:[email protected]://www.ihsdm.org/

Documents

IHSDM 2015 Overview