WORK ZONE PERFORMANCE MEASURE NEEDS

Conceptually, an agency can select from a wide range of potential measures for monitoring work zone safety and mobility performance. Examples of safety measures being used by some agencies include (3) :

• Crash statistics (frequencies, rates, and types; injuries and fatalities),
• Frequency of work zone intrusions,
• Speeds and speed variance,
• Percent of motorists exceeding the speed limit,
• Speeding citations issued,
• Service patrol or fire department dispatch frequency,
• Work zone inspection scores, and
• Worker fatalities and injuries.

Meanwhile, work zone mobility measures in use by certain agencies include:

• Delay,
• Queue length,
• Queue duration,
• Speeds,
• Volume-to-capacity ratio,
• Level of service,
• Volume (throughput),
• Percent of time operating at free-flow speed, and
• Percent of work zones meeting expectations for traffic flow.

For many of the safety and mobility measures listed, some exposure data and performance measure needs are also implied. Examples of exposure measures that have been used by agencies to normalize safety and/or mobility performance measures in work zones or to describe the amount of mitigation effort expended include:

• Vehicle-miles-travelled through the work zone,
• Number of vehicles passing through the work zone,
• Number of hours of work activity, and
• Hours of dedicated enforcement in the work zone.

Finally, some measures can actually cut across multiple categories. For example, user costs can be computed from the delay and crash data as another type of performance measure (4) . Likewise, customer surveys and complaints, although more commonly considered an indication of work zone mobility, may actually be influenced by both safety and mobility concerns.

PROJECT- LEVEL PERFORMANCE MEASURE NEEDS

An agency should begin the process of selecting work zone performance measures by examining its current goals, objectives, and thresholds of acceptability for work zone performance. Performance measures are desired which can be easily compared to those goals, objectives, and thresholds to see how well the agency is meeting these criteria. Agencies should also consider the types of traffic impacts analyses it performs during work zone planning and design. In many agencies, one or two impact assessment tools are used for most analyses because agency staff is most familiar with those tools (3) . One of the uses of work zone performance measures is to evaluate how well work zone impact assessments of planning and design decisions reflect what actually happens once the work zone is implemented in the field.

Not all work zones are created equal. One project may require just a few work activity periods that create intense delays (with several other work periods of no impacts to motorists), whereas another project may have a comparatively small, but consistent delay to motorists throughout the duration of the project. Both projects may thus generate the same amount of total delay overall, but would likely be perceived quite differently by the public. Therefore, agencies will typically also need to select more than one performance measure in each category to fully capture all facets of the impacts that are occurring.

With few exceptions, agencies have the option of choosing:

• When work should occur on a particular roadway,
• How much of the roadway to allocate to the work and how much to leave for traffic to use ,
• What construction strategies and techniques to use, and
• What techniques or strategies to use to mitigate the impacts of the work zone and improve roadway capacity, safety, traffic flow, etc.

The performance measures selected should allow agencies to assess the effectiveness of these types of decisions as well. It may be desirable to establish separate performance measures for different project phases, work operations, time periods during the day or night, or other criteria in order to better assess the ramifications of the decisions that were made. Depending on the measures selected, it may be necessary to obtain data during a few key days or weeks in an overall project (e.g., the first week of each phase change), rather than have to collect a large amount of data over the entire duration of a project. By being targeted and selective, an agency can maximize the effectiveness of its efforts to monitor and evaluate work zone performance.

Finally, some agencies have begun to monitor and track congestion and travel time reliability measures on an ongoing basis on certain roadways in its jurisdiction. Selected work zone performance measures should be compatible with other traffic-related performance measures the agency is using to evaluate overall operations.

AGENCY PROGRAM-LEVEL PERFORMANCE MEASURE NEEDS

Performance measurement begins at the project level, since that is where the impacts the agency is trying to manage occur. However, not meeting agency-established goals and objectives on a single project may not be indicative of an overall performance issue. Agency efforts to improve its policies, processes, and procedures (as required by the Work Zone Safety and Mobility Rule (1) ) will be enhanced if impacts are ultimately aggregated and interpreted across multiple projects.

One of the major challenges that agencies face is how to properly aggregate the performance measures computed for individual projects so that useful assessments across multiple projects can be made. For example, should an agency compute an average increase in crash rates across all work zones it has monitored, or compute separate averages for each type of roadway on which the work zones were located? Should the number of projects where queue length thresholds were exceeded be summed together, or should they be counted based on the type of work that was being performed (resurfacing, pavement rehabilitation, roadway widening)?

Many factors will influence the magnitude of work zone safety and mobility impacts that occur. Site characteristics, traffic volumes, and amount of truck traffic are just some examples. However, in terms of items under direct agency or contractor control, two main categories of decisions or actions exist:

• Type of work being performed (and how it is accomplished), and
• Traffic management approach used.

Agency program-level performance measures that are developed around these main categories will likely serve as a useful starting point for policy and procedure reviews.

As was recommended for developing project-level measures, agencies may be best served by taking an incremental, iterative approach. For example, an agency might initially target work zones that involve either long-term or regular short-term lane closures on its freeway facilities, and focus efforts on developing and interpreting performance measures from that set of projects. As the agency develops an understanding of the measures and makes improvements to its processes pertaining to freeway work zones, the agency may begin to monitor and assess work zones on major urban arterial roadways. Eventually, work zones on two-lane highways could be added as well. For some measures, such as fatal crashes, an agency may track the measure across all of its work zones as one measure of overall work zone safety. For other measures, such as delay, an agency may sample a portion of its work zones as this may provide a sufficient indication of whether congestion estimates during planning and design and management efforts during construction are working.

Regardless of how an agency chooses to implement work zone performance measures into its regular program review process, the intent should be to collectively assess how well the work zones being tracked meet the policies and objectives the agency has established. This can often be most easily achieved by developing rates across multiple projects under the agency’s jurisdiction for how often the agency’s policy goals and objectives are being met. This does not necessarily involve the monitoring or collection and processing of large amounts of data on all projects. Agencies typically have a good idea of which projects will not induce significant impacts, and those which will. In addition, those projects may only experience them during certain phases or work tasks. By focusing their efforts on key times, agencies can keep work zone performance monitoring and evaluation to a manageable level.

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