Transportation Management Plan Effectiveness Framework and Pilot
Chapter 5. Summary and Conclusions
Presently, very few agencies evaluate how well their impacts analysis results compare to what actually happens in the field, let alone assess how well the mitigation strategies employed affected the impacts of the work zone. Even for those strategies for which some assessments have been performed, the methods used and MOEs evaluated have varied widely, making it difficult to draw conclusions about how well the strategies would work as part of the TMP for an upcoming project. Therefore, this report was prepared to help practitioners formulate and follow clear, consistent approach towards assessing the effectiveness of TMP strategies. The report provides an inventory of the MOEs that each of the TMP strategies may affect at a particular work zone, depending on the characteristics of that work zone and other TMP strategies that are used. An overall framework is presented to guide analysts on the available approaches towards TMP strategy effectiveness evaluations, possible scopes of those evaluations, and potential analytical methods. A synthesis of evaluations is also for those TMP strategies for which previous and current literature and data were available.
TMP strategies attempt to mitigate impacts by:
- Increasing the amount of traffic-carrying capacity through the work zone or on alternative routes.
- Performing work that reduces capacity when traffic volumes are lower.
- Encouraging additional travel diversion away from the work zone beyond what would have happened otherwise.
- Reducing traveler surprise to unexpected conditions and features.
- Encouraging safer driving behavior through the work zone.
- Reducing the consequences of an errant vehicle leaving the travel lane relative to what would have happened if the mitigation strategy had not been employed.
- Reducing the consequences of crashes that do occur.
- Reducing other worker accident risks by providing more work space in which to operate.
- Reducing the duration of the work zone.
- Reducing public frustration and anxiety about the work zone.
Consequently, different MOEs are needed to evaluate the effectiveness of different strategies. In general, TMP strategies can be evaluated through one or more of the following MOE dimensions:
- Mobility.
- Safety.
- Customer satisfaction.
- Agency and contractor productivity and efficiency.
Many strategies affect MOEs in more than one of these dimensions, regardless of whether they are implemented specifically to mitigate work zone impacts within that dimension. Consequently, the effectiveness of multiple TMP strategies implemented at a work zone will often confound each other to generate an overall effect on impacts at that location. In some cases, methods do exist to dissect the influence of individual TMP strategies, but these typically require data from multiple projects and more advanced analytical techniques.
Multiple ways exist to assess whether a TMP strategy had some type of effect on one or more measures used to assess work zone safety and mobility impacts, specifically:
- Qualitative assessments.
- Quantitative assessments.
- Some hybrid of the two.
Meanwhile, assessments of TMP strategy effectiveness can also vary in scope. Common evaluation scopes include:
- Full-scale evaluation of all strategies on a project.
- Agency-wide evaluation of a single TMP strategy.
- Research evaluation of a single strategy implemented by several agencies.
- Case study of a single strategy at one location.
- Process review.
Ultimately, the selection of MOEs to use, assessment approach, and assessment scope varies depending on the question the practitioner is trying to answer, such as:
- Do we think this TMP strategy (or set of TMP strategies together) had some type of effect upon mobility, safety, customer satisfaction, and/or agency or contractor productivity and efficiency? In simplest terms, do we think this strategy was "effective?"
- How much of an effect did this TMP strategy/set of strategies have upon mobility, safety, customer satisfaction, and/or agency or contractor productivity and efficiency MOEs?
- How does the effectiveness of this TMP strategy/set of strategies upon mobility, safety, customer satisfaction, and/or agency or contractor productivity and efficiency vary as a function of differences in roadway, traffic, and work zone characteristics?
The challenges posed in assessing the effectiveness of TMP strategies to mitigate work zone impacts are particularly noteworthy. If introducing a work zone on a route adversely affects operating conditions on the route to a significant degree, a certain percentage of drivers will choose to alter their trip-making behavior by departing at a different time, changing their route, or perhaps even changing their choice of travel mode. This will occur even if no TMP strategies to encourage those changes are implemented. Conversely, the number of travelers modifying their trip-making behavior will affect how significantly the work zone itself affects operating conditions on that route. This same type of circular relationship between changes in trip-making decisions and the resulting operating conditions will also exist on alternative routes in the corridor. Therefore, strategies that attempt to also affect trip-making decisions and behaviors need to be measured not against what was happening before the work zone was introduced into the corridor, but rather measured relative to what would have occurred had the strategy not been implemented. In order to effectively accomplish such a comparison, a network-based model that performs route assignment and which can also represent the effect of TMP strategies being considered for a project is required.
Several studies performed over the past 25 years have made some attempt to assess the effects of certain TMP strategies upon work zone impacts. Although most have, to date, not focused on the four main MOE dimensions described above, they do provide some insight into the strategy influences on travel behavior that could be used to assess actual impact mitigation effects. In a few instances, syntheses of multiple study results were possible. Specifically, a range of effectiveness were developed and presented for the following strategies:
- Speed management techniques.
- Work zone ITS.
- Construction acceleration techniques.
- Increased transit service capacity.
- Night work (on safety).
