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SPR 667 – Assessment of Statewide Intersection Safety Performance. TAC Meeting August 31, 2009 2:00-3:30PM. Agenda. Meeting Objectives. Research Objectives. To quantify the safety performance of typical intersections  

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SPR 667 – Assessment of Statewide Intersection Safety Performance

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Spr 667 assessment of statewide intersection safety performance

SPR 667 – Assessment of Statewide Intersection Safety Performance

TAC Meeting August 31, 2009 2:00-3:30PM



Meeting objectives

Meeting Objectives

Research objectives

Research Objectives

  • To quantify the safety performance of typical intersections  

    • To assemble a statewide inventory of intersections including location, geometry, control and volume data.

    • To characterize by a variety of geometric, operational, and volume features the safety performance of typical intersections.

      • This performance will include both statistical summaries and exploration of the applicability of predictive models.

Review of tasks

Review of Tasks

  • Project Initiation – complete

  • Literature Review – complete

  • Data Assembly & Research Design – 90% complete

  • Pilot Study – 85% complete

  • Full Intersection Study – 20% complete

  • Summary Data Analysis – 20% complete

  • Develop Safety Performance Functions

  • Final Report

    Budget: $122,516

    Encumbered: $42,086 (34%)

    Balance: $80,430



  • Nearly 21% U.S. fatalities were identified as intersection or intersection-related (2007)

  • ITE estimates 50% of all reported crashes occurred at intersections

    • 55% of injury crashes

    • 48% of property-damage crashes.

  • Oregon (2007) intersection crashes accounted for 38% of total

    • 18% of fatal crashes

    • 39% of injury crashes

Literature review

Literature Review

  • PART 1

    • A summary of individual geometric, operation, traffic control, and other features

  • PART 2

    • Statistical summaries

    • Methods for pattern diagnostics

    • Modeling the safety performance at intersections.

Part 1 sources for intersection elements

PART 1Sources for Intersection Elements

  • Harwood et al. “Safety Effectiveness of Intersection Left- and Right- Turn Lanes”

  • Model Minimum Inventory of Roadway Elements (MMIRE)

  • Highway Safety Manual (HSM) Draft 3.1

  • Elvik and Vaa “Handbook of Road Safety Measures”

  • Other research

  • List is not exhaustive

Part 2 statistical summaries crash rates

PART 2Statistical Summaries (Crash Rates)

Spr 667 assessment of statewide intersection safety performance

Functional class

District or region

Part 2 statistical summaries

PART 2Statistical Summaries

Part 2 pattern diagnostics and proportions

PART 2 Pattern Diagnostics and Proportions

  • Excess proportions

    • HSM/Safety Analyst

  • Direct diagnostics

    • Comparisons of individual crash type proportions to all others

Part 2 safety prediction methods

PART 2 Safety Prediction Methods

  • Regression models

    • Negative Binomial models

    • Tree-based regression

    • Probit models

  • Urban – rural

  • Intersection type

  • Severity or crash type

  • Volumes significant in all models

Literature review conclusions

Literature Review Conclusions

  • Identified a long list of potential intersection elements

  • Crash rates varied considerably from state-to-state

  • Most summaries aggregated at relatively high level

  • Interestingly, all summaries used total crashes and did not develop separate injury rates or rates by any other crash category or causation.

    • Roundabouts were not included as separate category

    • Pedestrian or bicycle elements were also absent.

  • All of the summaries are “snapshots” in time and do not appear to routinely updated.

Literature review conclusions1

Literature Review Conclusions

  • Summarizing the crash data in terms of typical diagnostics appears to be very valuable effort.

  • Data requirements for predictive models are significant and a primary reason why there has been limited development.

  • The relationship of intersection characteristics with crash frequency, crash severity, and particular crash types is complex.

  • In nearly every model, volumes were a significant variable.

Data assembly

Data Assembly

  • ODOT CAR Code Setup Book

    • State highway system intersections (9,139)

    • Other system (143,186)

  • ODOT Crash Data System (via OrTSDA)

  • ODOT Digital Video Log (DVL)

  • ODOT Integrated Transportation Information System (ITIS)

  • Google Earth / GIS Files

  • Counts

    • Traffic counting firms

    • City/County Engineering & Planning Offices

    • PORTAL, Google Traffic

Intersection crash data

Intersection Crash Data

  • State Highway

    • Highway and milepost

  • City

    • Intersecting street numbers

  • County

    • Either mileposted or intersecting street numbers




Odot car code setup book

ODOT CAR Code Setup Book

Car setup book

CAR Setup Book

Remaining records “NULL” traffic control

Pilot study

Pilot Study

  • Objectives

    • Test data collection strategies

    • Define feasible data elements

    • Estimate effort

    • Help formulate likely data distributions

    • Test crash data scripts and summaries

  • All data elements

    • 49 NCHRP Flashing Yellow Arrow Intersections

    • 55 HSM Calibration Project Intersections

  • Partial data elements

    • 244 State highway–state highway intersections

Google earth map of intersections

Google Earth Map of Intersections

Data collection form

Data Collection Form

Data collection google earth

Data Collection: Google Earth

Google Earth can provide an aerial view of:

-Intersection Type-Turning Lanes



-Lat/Long Coord.


-Bicycle Facilities

-Ped. Facilities


-Length, Width

Data collection

Data Collection

  • Resolution is an issue in rural areas when making measurements.

John Day:

US 26 (005) and US 395 (048)

Digital video log

Digital Video Log

  • ODOT’s Digital Video Log provides street level views which can be used to identify:

    • Signalization-Intersections (ex: S = 3 = S)

    • # of Turning Legs-Medians and Channelization

Aadts from jurisdictions

AADTs from Jurisdictions

Counts from traffic firms

Counts from Traffic Firms

Variable summary n 104

Variable Summary (N=104)

Variable summary n 1041

Variable Summary (N=104)

Crash frequency n 347

Crash Frequency (N=347)


Crash rates n 254

Crash Rates (N=254)


Crash patterns

Crash Patterns


Crash patterns by vehicle movement

Crash Patterns By Vehicle Movement

Draft results from pilot study

Draft Results from Pilot Study

  • Many elements probably not needed for summaries / patterns

  • Crash script developed

    • Refining / testing in Access database

    • Quality control checks needed

  • Traffic volumes

    • Hardest to get (off state system)

    • Time challenge (year of data collection)

    • Still some other avenues to pursue

  • Signal timing

  • Need to study appropriate aggregations

Work plan deliverables

Work Plan Deliverables

  • 1 - Literature review

  • 2 - Brief memo to TAC summarizing findings, progress, and recommendations for pilot study intersections and scope

  • 3 - Interim report summarizing findings of the pilot study, progress, and recommendations for full field study. Preview of statistical summaries that will be conducted.

  • 4 - Interim report summarizing the results summary data analysis

  • 5 - Final report

Revised work plan

Revised Work Plan

  • Discussion

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