EXECUTIVE SUMMARY
Work zone performance measures are metrics that help to quantify how work zones impact travelers, residents, businesses and workers. Some measures describe the impacts of a specific work zone (project-level metrics), whereas other measures describe the impacts of a set of work zones (agency program-level metrics). What is expected to occur at a work zone with regard to safety or mobility impacts can be quite different from what is ultimately experienced at a site. Every work zone is unique, and the combined effects of design decisions, work phasing and sequencing operations, and impact mitigation strategies implemented at a site can be challenging to predict beforehand. Work zone performance measures help agencies improve their understanding of how their decisions during planning, design, and construction affect work zone safety and mobility, and thus can help improve how they make decisions for future work zones.
Work zone performance measurement does not need to be an overwhelming activity for an agency. Not all work zones need to be measured, and those work zones that are measured do not necessarily need to be monitored at all times. Work zone performance measurement should be driven by agency and other stakeholder needs and priorities. One advantage of establishing work zone performance measures is that it focuses attention on what is considered important to the agency and stakeholders.
To be useful, it is important for agency staff to understand:
- What is being measured,
- How it is being measured, and
- Why it is being measured.
Efforts to improve work zone policies, processes, and procedures will be more effective if agencies also look at measures across multiple projects to assess their overall efforts and outcomes. Tracking how often an agency meets its performance expectations for work zone safety and mobility across multiple work zones can be more indicative of overall performance and useful as program-level performance measures.
Agencies should choose a few good measures carefully based on their particular needs and characteristics, communicate those to all stakeholders and staff, and track them clearly, seriously, and consistently. Three basic types of performance measures are useful to quantify work zone safety and mobility impacts:
- Exposure measures,
- Safety measures, and
- Mobility (traffic operations) measures.
Exposure measures describe the amount of time, roadway space, and/or vehicle travel that a work zone or a collection of work zones affects or requires. Safety measures describe how crash risk has changed for the individual motorist and/or for the traveling public in general, relative to pre-work zone levels. Safety measures can also be defined for contractor or agency personnel working on the roadway. Finally, mobility (traffic operations) measures describe how travel mobility has been affected for motorists (and potentially other types of travelers as well).
Work zone performance measures should:
- Relate to the safety and mobility goals and objectives that the agency has established for itself,
- Be consistent with the measures used in impact assessment efforts for work zone planning and design analyses,
- Characterize the different facets of impacts that are occurring,
- Enable the agency to evaluate the effects of alternative strategies for mitigating traffic impacts caused by work zones, and
- Be compatible with other performance measures that an agency is using to evaluate its system.
Once work zone performance measures have been selected, agencies need to define the data sources, collection techniques, and calculation methodologies that will be used to compute those measures. For some measures, only one data source and/or methodology will exist for an agency; for others, several sources and methodologies may be available. Agencies must balance the data needs for performance measures with available resources and other factors to determine the most appropriate sources or methodologies to use.
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