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

Work Zone Performance Measurement - Mobility

slide 1: Work Zone Performance Measurement - Mobility

Work Zone Peer Exchange

May 2013
Atlanta, GA

Texas A and M Transportation Institute logo.


slide 2: Mobility-Related Performance Measures


Mobility impacts commonly measured as

  • Throughput
  • Delays
  • Travel times
  • Travel time reliability
  • Vehicle queues

slide 3: Throughput Performance Measures


  1. Reduction in maximum vehicle throughput flow rate
    • Overall
    • During certain work tasks
    • When work zone inactive
  2. Maximum person throughput flow rate

slide 4: Throughput


Existing Agency Data Sources

  • TOC or traffic signal system vehicle count data
  • Toll facility usage data
  • Automatic traffic recording (ATR) station data
  • Planning and programming AADT estimates

Work Zone Specific Throughput Data

  • Data from work zone ITS deployment
  • Temporary mechanical data collection device
  • Manual vehicle count at key times & locations

Person Throughput Data

  • Manual sampling of per-vehicle occupancy levels
  • Manual sampling or video detection of pedestrian throughput

Two cameras mounted on a street sign structure.

A worker next to a road tube traffic counter.

slide 5: Throughput


Potential Future Data Source

  • Connected vehicle technology (sufficient market penetration of V2V and V2I technology will be needed).

Modified photo shows merging vehicles overlaid with concentric circles indicating vehicle-to-vehicle and vehicle-to-infrastructure communications.


slide 6: Throughput


Illustration of a non-congested lane closure. Diagram depicts a lane closure where demand is less than capacity and throughput equals demand, resulting in no congestion.

Illustration of a congested lane closure. Diagram depicts a lane closure where demand exceeds capacity and throughput equals capacity, resulting in congestion.


slide 7


Data Source Key Considerations and Trade-offs
All data types
  • Is it a demand or throughput measurement?
  • Multiple days of data is needed to reduce day-to-day variations
TOC sensor data and toll facility usage data
  • Important to verify data will be available once work has started
ATR station data
  • Important to verify that counts are "true" values (not adjusted)
Agency AADT estimates
  • Overestimates throughput and exposure if diversion occurs
Work Zone ITS Data
  • Important to verify that data will be archived
Mechanical counters or manual counts
  • Not practical for high-volume, high-speed roadways
  • Labor intensive
Manual collection of person/vehicle occupancy levels
  • Useful for evaluating non-vehicular travel mitigation strategies
Manual or electronic collection of pedestrian throughput
  • Useful if non-vehicular travel mitigation strategies
  • Pedestrian and vehicle peak hours may not coincide
Connected Vehicle Data
  • Date of availability still uncertain

slide 8: Travel Time and Delay Performance Measures


  • Average unit travel times (or changes in unit travel times)
    • Corridor-based (when multiple work zones)
    • During specific periods or work tasks
  • Average delays per vehicle
  • Percent of time when delays exceed threshold
  • Total delay (veh-hrs)

slide 9: Travel Time and Delay Measures (cont’d)


  • Time required to convey delay information to travelers
  • % of projects exceeding delay thresholds
    • Maximum value
    • Allowable duration
  • % of travelers experiencing delays
    • Corridor or region-wide
    • In a specific project

slide 10: Travel Time Reliability Performance Measures


  • Change in "xx"-percentile travel times
    • Project
    • Corridor or route
  • Change in planning time index
    Equation. Planning index equals the result of average travel time divided by freeflow travel time.
  • Change in buffer index
    Equation. Buffer index equals the result of the "xx"-percentile travel time divided by average travel time.

slide 11: Delay, Travel Time, Travel Time Reliability


Existing Agency Data Sources

  • TOC spot speed sensor data
  • TOC tracking of vehicles through use of cameras
  • TOC point-to-point travel time data using AVI, AVL, or license-plate recognition technology

Work Zone Specific Travel Time and Delay Data

  • Data extracted from a work zone ITS deployment
  • Portable point-to-point travel time data collection devices
  • Manual spot speed sampling using radar or lidar devices
  • Travel time runs through the work zone
  • Estimation of travel time delays from observed queue length data

This image shows a pole-mounted sensor.


slide 12: Delay Estimation from Observed Queue


Equations explaining how to estimate delay from the observed queue.

slide 13: Delay, Travel Time, Travel Time Reliability


Potential Future Data Source

  • Travel Times from Bluetooth Address Matching
  • Private (3rd Party) Sources of Travel Time and Speed Data
  • Connected vehicle technology

slide 14


Data Source Key Considerations and Trade-offs
TOC spot speed data
  • Less accurate when congestion is present
  • Important to verify data availability once work has started
TOC point-to-point travel time data
  • Important to verify data availability once work has started
Work zone ITS Data
  • Data must be archived and available for PM computations
Portable point-to-point travel time data collection
  • Accuracy depends on market penetration of technology
  • Time lags exist during congestion.
Manual spot-speed data
  • Labor intensive
  • Most useful if the impacts occur in a fairly small section
  • Most useful for assessing short time periods
Manual travel time data collection
  • Labor intensive
  • Most useful for assessing short time periods
  • Multiple runs increase accuracy and precision
3rd party travel time and speed data
  • Level of detail available may vary by vendor
  • Translation to agencies' data mapping protocol is needed
Bluetooth data
  • Accuracy depends on market penetration
  • Time lags exist during congestion
Connected Vehicle Data
  • Date of availability still uncertain

slide 15: Traffic Queue Performance Measures


  • Average queue duration
    • Overall
    • During certain times or tasks
  • % of time when queues occur
    • Overall
    • Those exceeding a threshold level
  • Maximum queue length
    • Project
    • Combined along route or corridor

slide 16: Traffic Queue Measures (cont’d)


  • Average queue length
    • Overall
    • During certain phases or work tasks
  • % of projects with queues exceeding thresholds
    • Maximum length
    • Maximum duration
  • % of travelers experiencing a queue

slide 17: Traffic Queue Data Sources


Existing Data Sources

  • Speed data extracted from a work zone ITS deployment
  • Observation of queues from a permanent or work zone TOC
  • Observation of queues by field personnel at the work zone

Queue Length Estimation from Spot-Speed Sensors

This is a four-step process diagram. The steps are 1) divide the roadway into regions of assumed uniform speed; 2) examine speeds and volumes hour-by-hour at each sensor location; 3) compare hourly speed/volume profiles across sensors to identify length of queue; 4) sum region lengths where speeds are below thresholds.


slide 18


  • Spot traffic sensors are located 0.2 mile, 0.8 mile, and 1.3 miles upstream
  • Project diary information indicates that a lane closure began at 9:00 AM and ended at 3:30 PM.
Time Estimated Location of Upstream End of Queue Estimated Queue Length
11:00 am None 0
12:00 pm Between Sensors 1 & 2 0.2 + (0.6 / 2) = 0.5 mile
1:00 pm Between Sensors 2 & 3 0.2 + 0.6 + (0.5 / 2) = 1.05 mile
2:00 pm Between Sensors 2 & 3 1.05 mile
3:00 pm Between Sensors 2 & 3 1.05 mile
4:00 pm None 0

Examples of travel speeds during a lane closure

slide 19: Traffic Queue Data Sources

Potential Future Data Sources

  • Screen shot Captures from 3rd Party Traveler Information Providers
  • Private (3rd Party) Sources of Travel Time and Speed Data
  • Connected vehicle technology

Screen capture of a Google Map with the traffic layer turned on. Modified photo shows merging vehicles overlaid with concentric circles indicating vehicle-to-vehicle and vehicle-to-infrastructure communications.


slide 20


Data Source Key Considerations and Trade-offs
All data types
  • Definition of queues (e.g., min speed threshold) is critical
  • Both queue duration and queue length are important
TOC or work zone ITS data using spot speed sensors
  • Requires speed analysis on sensor by sensor basis
  • Important to verify data availability once work has started
Visual queue identification by TOC operators
  • Requires good camera coverage upstream of work zone
Collection of queue data by field personnel
  • Data collection protocol training is needed
  • May be difficult to accurately monitor the end of queue
Screen shot of real-time traffic condition maps
  • Required screen resolution depends on expected queue length
  • Time-lapse capabilities do not exist in most screen capture software
3rd party traveler information data
  • Level of detail available may vary by vendor
  • Translation to agencies’ data mapping protocol is needed
Connected vehicle data
  • Date of availability still uncertain

slide 21: Discussion


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

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