Work Zone Mobility and Safety Program
Work Zone Performance Measures Pilot Test - Table of Contents

EXECUTIVE SUMMARY

Transportation professionals are increasingly pressed to demonstrate sound management decisionmaking and resource allocation. Performance management is a method to quantify and improve performance, and engage and communicate with citizens and other stakeholders. One of the challenges facing state Departments of Transportation (DOTs) is to determine how to best measure and track safety and mobility impacts associated with highway work zones. The development and use of work zone safety and mobility performance measures can be valuable to agencies in several ways, including the following:

  • They allow agencies to quantify how work zones are impacting motorists, and how actions being taken (management strategies, technologies deployed) to mitigate those impacts are or are not working.
  • They assist agencies in making investment decisions, developing and improving policies, and defining program priorities.
  • They assist agencies in communicating with elected officials and with the public.

This report describes the results of a pilot test conducted to assist state DOTs in identifying the following:

  • What work zone performance measures can and should be targeted?
  • What data is needed to compute the measures?
  • What methods exist to obtain that data?

In addition, the test was designed to generate practical guidance, lessons learned, useful tips, etc., that state DOTs could use to initiate and/or improve upon a successful work zone performance measurement program.

A series of potential work zone performance measures were developed to address potential state DOT needs under each of the following five priority categories:

  • Exposure
  • Traffic queuing
  • Traveler delay
  • Travel time reliability
  • Safety

For the pilot tests, emphasis was placed on collecting the needed data and performing the necessary computations for the measures in four of the five categories. Safety performance measures were excluded from the pilot test effort because of the potential for significant lag times in obtaining crash data at the pilot test locations, and because safety performance measures themselves are fairly well-defined and understood. For the remaining categories, the proposed performance measures in each category were pilot tested at five different projects nationally:

  • I-95, Lumberton, North Carolina
  • I-95, Philadelphia, Pennsylvania
  • I-405, Seattle, Washington
  • I-15/US95 Design-Build Project, Las Vegas, Nevada
  • I-15 Express Lane Project, Las Vegas, Nevada

In addition, two different methods for collecting the data necessary to compute the performance measures were also tested (to the extent possible) at each project:

  • Electronic traffic surveillance data of conditions (e.g., speeds) at particular points on the roadway, or of elapsed travel time along a particular roadway segment
  • Manual observations of queue durations and lengths by field personnel during work activities.

The performance measures computed with each type of data were compared to each other, and to ground-truth measurements of travel times, delays, and queues made by research staff. Key findings with regard to the computation and use of work zone performance measures were as follows:

  • Work activity measures (percent of days worked, average hours per day of work) is useful in tracking and comparing contractor level of effort.
  • Capturing lane closure hours (percent of hours involving 1, 2, etc. lanes closed) is relevant only if total lanes remaining open is also captured.
  • The percent of time when queues exceed selected threshold values should be useful as a potential performance specification for work zone traffic control and impact mitigation.
  • The measure “percent of traffic encountering a traffic queue” provides a direct indication of the breadth of impacts of the work zone to the motoring public.
  • The average duration of queues, average queue length, and maximum queue length all have value for assessing both project-level and process-level traffic management decisions pertaining to work zone mobility.
  • The average delay per queued vehicle, along with the percent of traffic encountering a queue, appears to be a straightforward way to account for both the intensity and breadth of work zone impacts on motorists.
  • The buffer index, as a travel time reliability measure for work zone performance monitoring, appears to offer useful insights into another dimension of user impacts due to the work zone at locations where recurrent traffic congestion already exists prior to the start of the project.

Key lessons were also learned with respect to data collection and analyses of work zone exposure and mobility data, and include the following:

  • Estimates of queue lengths need to include a description of the location of the queue relative to the lane closure (upstream, beyond taper and into work zone, partially upstream and partially within the work zone, etc.).
  • Field personnel documentation of when and where lane closures were placed and hours of work activity will still be needed to compute mobility performance measures, even if electronic traffic surveillance data is being used to monitor traffic conditions.
  • It is important to make sure that the traffic sensors themselves will remain operational when construction begins.
  • The level of accuracy in work zone mobility performance measurement achievable with electronic traffic surveillance data depends heavily on the design of the system (particularly traffic sensor spacing).

To assist practitioners in applying the findings and lessons learned from this pilot test effort, a primer on selecting and computing work zone performance measures is being developed to accompany this report.

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