Work Zone Mobility and Safety Program
Work Zone Performance Management Peer Exchange Workshop

Work Zone Performance Measurement – Safety

slide 1: Work Zone Performance Measurement – Safety

Work Zone Performance Management Peer Exchange Workshop

May 8, 2013
Atlanta, Georgia

Texas A&M Transportation Institute logo


slide 2: Safety-Related Performance Measures

Safety impacts commonly measured as

  • Crashes
  • Safety Surrogates
  • Worker Accidents

slide 3: Work Zone Crash Performance Measures


  • # Crashes or change in # of crashes
    • Per time period(s) of interest
  • Change in crash rate per vehicle mile traveled
    • Per time period(s) of interest
    • Aggregated across projects
  • Change in % distribution of crashes by severity, type, manner of collision, etc.
  • Change in crash costs

slide 4: Crashes


  • Existing Agency Data Sources
    • Statewide traffic crash records database entries
    • Crash report forms (hard-copy or electronic)
    • TOC incident database entries
    • Emergency response/service patrol dispatch logs
  • Future Sources
    • Agency-collected work zone crash information
    • Connected vehicle initiative data

slide 5:


Data Source Key Considerations and Trade-offs
Statewide Crash Records Database
  • Limited work zone features and activities information
  • Time lags in obtaining crash data for a given work zone
Electronic or hard copy crash report forms
  • Limited work zone features and activities information
  • Requires manual coding
  • May need to work with multiple enforcement agencies
TOC operator incident logs
  • Includes non-reported as well as reported crashes
  • Includes non-crash events
Dispatch Logs of Emergency Response or Service Patrols
  • Likely to include non-traffic crash events as well
  • Potential privacy concerns
Agency-collected crash and work zone database
  • Significant agency effort required
  • Requires upper agency support and emphasis
Connected vehicle data
  • Date of availability still uncertain

slide 6: Tracking Crash Frequency Trends


Case 1:

  • Work zone on roadway that normally experiences 5 crashes per month
  • Have had 7, 3, 10, 7 crashes in past 4 months during work zone (+40%, -40%, +100%, +40%)

A crash freqency trends chart shows the number of crashes expected if the work zone had not occurred (x-axis) and minimum number of crashes in the work zone that would indicate that craashes have increased relative to expectations (y-axis). The chart plots a line signifiying an increase in crashes significantly greater than 20 percent and a line signifying an increase in crashes is significantly greater than 0 percent. Two red dots appear between the lines and a red dot appears on each line.


slide 7:


A crash freqency trends chart shows the number of crashes expected if the work zone had not occurred (x-axis) and minimum number of crashes in the work zone that would indicate that craashes have increased relative to expectations (y-axis). The chart plots the trend curve for a 90 percent chance, 75 percent chance, and 50 percent chance that crashes have increased. Two red dots appear above the 50 percent chance line and two appear below it. The graph is labeled "Nugenix"


slide 8:


Typical Number of Crashes Actual Crashes in Work Zone Change for Month
75 90 20%
75 100 33%
70 100 43%
60 80 33%

slide 9:


A crash freqency trends chart shows the number of crashes expected if the work zone had not occurred (x-axis) and minimum number of crashes in the work zone that would indicate that craashes have increased relative to expectations (y-axis). The chart plots the trend curve for a 90 percent chance, 75 percent chance, and 50 percent chance that crashes have increased. Two red dots appear above the 50 percent chance line and two appear below it.


slide 10:


A crash freqency trends chart shows the number of crashes expected if the work zone had not occurred (x-axis) and minimum number of crashes in the work zone that would indicate that craashes have increased relative to expectations (y-axis). The chart plots the trend curve for a 90 percent chance, 75 percent chance, and 50 percent chance that crashes have increased. A series of red dots indicate "Series 1".


slide 11: Work Zone Safety Surrogate Performance Measures


  • Speeds
    • Compliance percentage
    • Variance
  • Change in emergency response dispatches
  • Work zone inspection scores
  • Frequency of erratic maneuvers
    • High deceleration rates
    • Short times-to-collision (headways)
    • Forced merges

slide 12: Safety Surrogates


  • Existing Agency Data Sources
    • Speed data collected by hand-held devices
    • Speed data extracted from ITS sensors
    • Travel times
    • Videotaped traffic behaviors at key locations
    • Work zone inspection scores
 A speed data report screen.
Source: Oregon DOT
  • Future Sources
    • Microscopic traffic simulation output
    • Connected vehicle initiative data

Screenshot of a microsimulation output screen.


slide 13:


Data Source Key Considerations and Trade-offs
All data types
  • Correlation to crashes not yet fully verified
  • Most can be obtained relatively quickly
TOC or work zone ITS speed sensor data
  • Value of data depends on the locations of the sensors.
  • Need to verify data availability and archival once work starts
Speed data collected with hand-held radar or lidar
  • Data collection easy to accomplish
  • Useful for assessing speed behaviors
  • Inconspicuous data collection techniques required
Travel times through the work zone
  • Speed change locations can indicate problems
  • Can be used to assess compliance with wz speed limit
Videotaped traffic behavior
  • Can be difficult to find a unobtrusive viewing point
  • Data analysis is labor intensive
  • Requires precise definition of behaviors of interest

slide 14:


Data Source Key Considerations and Trade-offs
Work zone inspection scores
  • Requires significant effort to establish scoring/ratings
  • Correlation of scores to actual safety levels not yet verified
Traffic simulation output (analyzed with SSAM)
  • Significant coding and calibration effort required
  • Correlation to actual work zone safety conditions not yet verified
Connected vehicle data
  • Date of availability still uncertain

slide 15: Worker Accident Performance Measures


  • Frequency of worker accidents
  • Worker injury rates per hours of work
  • Distributions of injury types, contributing factors

slide 16: Worker Accidents


  • Existing Agency Data Sources
    • Agency or contractor worker injury records
    • State worker compensation commission accident statistics
    • Bureau of Labor statistics database
  • Future Sources
    • Connected vehicle initiative data

slide 17:


Data Source Key Considerations and Trade-offs
Agency or contractor worker injury records
  • Use must be monitored due to privacy concerns
  • Small sample size for many companies will make it difficult to identify trends
State worker compensation commission statistics
  • Useful for comparisons to agency or contractor accident trends
  • Level of detail will be limited
BLS, OSHA worker accident statistics
  • Useful for comparisons to agency or contractor accident trends
  • Level of detail will be limited
Agency-collected work zone crash and accident database
  • Significant effort required
  • Requires upper agency support and emphasis
  • Use of accident reports must be monitored carefully due to privacy concerns

slide 18: Discussion


  • Are there other Safety-related measures you have thought about using in your agency? Why are you considering those?
  • How would you use these or other safety measures to decide how to modify your agency's current policies or practices?

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