Guidance for Conducting Effective Work Zone Process Reviews

Chapter 3. Eddective Use of Data and Performance Measures in Process Reviews

Importance of Data and Performance Measures

The Work Zone Rule requires SHAs to “continually pursue improvement of work zone safety and mobility by analyzing work zone crash and operational data from multiple projects to improve State processes and procedures.” To date, most process reviews have relied extensively on field reviews of temporary traffic management and control plan implementation quality, project inspections, examination of statewide work zone crash counts (typically work zone fatalities), and staff questionnaires and interviews as the data to be analyzed. However, field reviews and inspection scores typically provide only a final snapshot perspective of traffic control plan implementation and maintenance quality, rather than an overall assessment of an agency’s entire work zone safety and management program. Likewise, crash statistics provide some insight into work zone safety, but such measures also require exposure data in order to generate useful information on the effectiveness of work zone safety policies and procedures across the agency. Even questionnaire/interview responses of agency staff provide only a subjective view of work zone safety and mobility management efforts and perceived effectiveness.

Outcome-based performance measures describe how much effect work zones have on safety and mobility in terms of increases in crash risk, travel times, travel time reliability, or level of customer satisfaction (the traveling public, business owners, etc.) with travel conditions. Traditionally, agencies have not emphasized the collection and analysis of outcome measures of work zone safety and mobility. Fortunately, technology advances in recent years have increased the availability and timeliness of both mobility and safety data on major roadways and in work zones. Consequently, agencies should consider the opportunities to make use of such data as part of their process reviews.

Technology advances in recent years have increased the availability and timeliness of both mobility and safety data in work zones.

Examples of Data and Performance Measures for Work Zone Process Reviews

FHWA has published guidance on data needs and availability for work zone performance measurement as well as a primer on work zone performance measures (see https://ops.fhwa.dot.gov/wz/resources/publications/fhwahop13011/index.htm and https://ops.fhwa.dot.gov/wz/resources/publications/fhwahop11033/index.htm). SHAs refer to these resources to help include outcome-based measures in their process reviews. In general terms, agencies will need to gather and collate three different types of data:

• Exposure data – estimated or actual volumes, vehicle occupancies, pedestrian counts in and possibly around some of its work zones;
• Indicator/stratification data – times when certain work zone conditions and traffic control features were present at those work zones being examined. This data is combined with exposure data to focus on high-impact times such as when work activity is occurring or when temporary lane closures are in place; and
• Performance data – measuring how much those work zones being examined affected crashes, travel times, or customer satisfaction levels.

Mobility Performance Measures

Mobility data and measures for work zone process reviews can be used in at least two ways:

• To assess the degree of compliance with stated objectives or performance thresholds in the agency's work zone policy or procedures; and
• To assess changes in absolute measures pertaining to work zone mobility observed from one process review to the next.

Project staff can gather data on queues, travel times, etc. for certain time periods (such as peak periods, during temporary lane closures, etc.), but the accuracy and thoroughness of data collection efforts must be carefully monitored. Performance data can also be obtained from electronic traffic sensors on site or from private-sector data. These data can then be analyzed in terms of frequency of violation of target thresholds and/or the extent by which the threshold was exceeded. Once the collection and analysis procedures have been established and institutionalized, comparison of the measures from one process review to the next can illustrate whether work zone mobility performance is improving, being maintained, or degrading. Differences in performance measures for certain subsets of projects (those involving long-term lane closures, for example) may suggest a need for additional changes in agency policies and procedures for those types of projects.

Example Mobility Measures Useful for Process Reviewsa Compliance with Mobility Goals, Stated Thresholds Percent of significant projects with more than 10 events exceeding the maximum delay threshold stated in the agency’s policy Number of events during all significant projects where the maximum delay threshold was exceeded Absolute Mobility Measures and Changes over Time from Pre-Work Zone Conditions Average delay per vehicle during peak hour for significant projects examined Change in 95th percentile travel time experienced during a project Percent of time when queues existed at a project Percent of significant projects that experienced more than 5 events that exceed the maximum queue length and duration threshold stated in the agency’s policy Change in number of hour-miles along the facility with operating speeds less than 40 mph

Safety Performance Measures

Some agencies have also established safety-related goals and performance metrics as part of their work zone safety and mobility policy. Crash data is the most direct indicator of safety, but can be challenging to obtain in a timely manner. Safety surrogate data, typically speeds or erratic maneuvers, are easier to obtain but more difficult to interpret with respect to how safety is affected. Worker injury data may also be considered. Both crash and worker injury data are usually sparse for shorter duration projects.

Example Safety Measures Useful for Process Reviewsa Compliance with Safety Goals, Stated Thresholds Percent of significant projects that experienced statistically significant increases in crash frequency Average increase in crashes across the significant projects examined in the process review Absolute Safety Measures and Changes over Time from Per-Work Zone Conditions Change in crash rate per-vehicle-mile traveled during peak and off-peak periods throughout construction Percent of vehicles exceeding the posted work zone speed limit by more than 10 mph Frequency of forced merges per 1000 lane closure vehicle passages Worker injury rates per 200,000 worker-hours (for comparison to the national BLS injury rate)

A methodology useful for work zone safety performance measurement is to estimate what the expected frequency of crashes would have been on a segment of road if the work zone had not been present, and compare that to the frequency of crashes that actually occurred during the project. Some agencies have used simple 3-year averages prior to construction as the expected crash frequency, whereas others have begun to employ more sophisticated crash prediction methods such as those documented in the Highway Safety Manual. The advantage of the more advanced methods is their ability to better address regression-to-the-mean and other statistical challenges associated with analyzing crash data; however, they do require special training to use and more data to properly apply.

Customer Satisfaction Performance Measures

In many cases, customer satisfaction performance measures may correlate with the mobility and safety measures described above. However, customer satisfaction measures will also reflect the results of agency and contractor efforts to mitigate these mobility and safety impacts. The traveling public generally understands the need to perform roadway repair and improvements, but is frustrated when efforts to keep them informed and/or minimize the inconvenience are not made. This is why public information efforts are so important for those significant projects that are expected to cause safety and mobility impacts.

Example Customer Satisfaction Measures Useful for Process Reviewsa Compliance with Customer Satisfaction Goals, Stated Thresholds Percent of significant projects receiving more than 5 complaints per month Percent of customer satisfaction scores statewide below a “Good” value Absolute Customer Satisfaction Measures and Changes over Time Average rating scores for each survey question (e.g., “How easy is it to safely travel through work zones you encounter?”)

The most common method of obtaining customer satisfaction performance measures is through the use of surveys (one-on-one, focus groups, online/email, etc.). Social media is also seeing increased use as a tool for assessing customer opinions.

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