Work Zone Mobility and Safety Program
Table of Contents

EXECUTIVE SUMMARY

Performance measures quantify how a particular work zone or several work zones together are affecting traveler safety and mobility. In addition, performance measures can help agencies and contractors assess if and how their work zone safety and mobility policies, processes, and procedures are working well or should be improved. In the context of highway work zones, there are three major data needs for performance measurement:

  • Performance data (“how much” a work zone affects travelers, the agency, and/or contractor);
  • Exposure data (“who” or “what” are being affected); and
  • Work zone indicator or stratification data (“when” or “where” the effects are occurring).

With regards to how much work zones affect conditions, four categories of performance data are viewed as important:

  • Mobility – data that characterize how trip duration for an individual or the number of trips being made are affected by a work zone;
  • Safety – data that characterize how risks to travelers and highway workers are affected by a work zone;
  • Customer satisfaction – data that characterize how travelers, residents, and business owners in or near a work zone perceives its effect on them; and
  • Agency and contractor efficiency and productivity – data that can be used to assess contractor/agency efforts to minimize the duration and extent of travel impacts from a work progress perspective.

Within the mobility category, performance data can be further subdivided into the following subcategories:

  • Throughput;
  • Unit travel times or delay;
  • Travel time reliability; and
  • Traffic queues.

Likewise, the safety performance category can be further divided into the following:

  • Traffic crashes;
  • Operational safety surrogates; and
  • Worker accidents.

Exposure data categories include:

  • Counts or distances traveled through work zones by travelers or vehicles;
  • Project, phase, activity durations (such as hours of work activity), or worker-hours in the field; and
  • Number of phases or activities that occur.

Meanwhile, indicator or stratification data categories include:

  • General roadway design characteristics (type of road, normal number of travel lanes, shoulder presence and size, speed limit, etc.) before the project began, and design characteristics of interest within the work zone (lane and shoulder widths, long-term lane closures, design characteristics of crossovers and lane shifts, etc.);
  • Locations and times of work activities of interest (temporary lane closures, full road closures, etc.) and dates of major phase changes; and
  • Time and characteristics of events of interest (weather events, major incidents, special events, etc.).

There are several ways practitioners may obtain data for use in work zone performance measurement. One method for accessing data is to extract it from existing sources. Another method is to specifically collect the data of interest through a variety of methods. Lastly, data may be interpolated or estimated from existing or collected data sources. For exposure and indicator or stratification data (which are used to compute many of the specific performance measures presented later in this document), it typically requires digging into project-specific files and databases, culling the desired data from them (usually by hand), and then collating and correlating these data with the performance data.

Overall, work zone performance measure selection and use involves five main steps:

  • Step 1. Determine the categories of work zone performance that are of interest
  • Step 2. Decide which work zones will be measured
  • Step 3. Decide what work zone conditions are of most value to measure
  • Step 4. Determine what data sources are available for computing performance measures at each work zone of interest, and assess their potential usefulness and limitations
  • Step 5. Identify and compute specific performance measures of interest

Several sources of data exist for most of the performance measure subcategories of interest. These are identified, along with the key considerations regarding their application for work zone performance measurement, throughout this guidance document. A set of recommended performance measures that could be computed with the available data, prioritized by the expert practitioner panel assembled for this project, are also presented throughout the document.

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