Mitigating Work Zone Safety and Mobility Challenges through Intelligent Transportation Systems Case Studies: Chapter 6 - FHWA Work Zone
CHAPTER 6 - SUMMARY OF KEY CONCEPTS
As this nation’s roadway infrastructure continues to age, more and more work zones will be needed to repair, rehabilitate and reconstruct this infrastructure. At the same time, the demand for travel on this infrastructure is likely to also rise, meaning that the work zones that do occur will generate significant adverse impacts on safety, mobility, traveler satisfaction, and highway work crew productivity.
Fortunately, research and experiences over the past 10+ years have made it clear that properly designed and implemented intelligent transportation systems (ITS), implemented as part of a well thought out transportation management plan (TMP), can help mitigate these work zone impacts. However, ITS is only one tool within a TMP designer’s toolbox. A systems engineering decision process should be followed to determine whether an ITS deployment is the best mitigation strategy to deploy for a particular work zone, and to determine the appropriate ITS devices, systems, and/or strategies to implement. Although the overall scope of a given project ultimately determines the complexity and level of effort required for this systems engineering design process during planning, it should apply to the range of deployments, from small-scale, temporary deployments lasting a few months using commercial off-the-shelf (COTS) systems to complex, multi-year ITS deployments that may eventually be incorporated into permanent traffic monitoring and management systems. This process consists of five key steps:
- Defining the problem.
- Specifying the requirements of a solution.
- Identifying and evaluating alternatives, as necessary.
- Selecting, designing, and implementing the best solution.
- Evaluating (i.e., describing the lessons learned).
This report documented work zone ITS deployments at five case study sites. These case studies illustrate four different ways in which ITS was used to address certain work zone challenges:
- Using Commercial Off-The-Shelf ITS to Mitigate High-Speed Rear-End Work Zone Crashes,
- Using ITS for Traffic Mobility Performance Specification Monitoring,
- Supplementing an Existing Permanent ITS to Manage Traffic During Construction, and
- Using Permanent ITS to Manage Work Zone Traffic.
Numerous lessons learned can be gleaned from these five case study sites for each step of the engineering design process, as presented below.
Defining the Problem
A well-defined problem is an important first step and the basis for all subsequent steps in the systems engineering process for crafting an appropriate solution, which may or may not require work zone ITS. It is also important to drill down beyond the obvious general concerns about congestion, delays, and crashes to understand the true “problems” underlying those concerns. Failing to define the problem well can result in an overly costly or unnecessary system that fails to address any real need.
In the Illinois case studies, for example, concerns existed over unpredictable queues occurring at work zone bottleneck locations due to varying traffic demands on the facilities, as well as the incidents that occur which could not be quickly moved out of available travel lanes due to a lack of shoulders. Conversely, for the Utah Bangerter Highway case study, lacking the capability to accurately monitor and assess individual motorist delays was the main problem in trying to develop and implement a mobility-related performance specification for contractors. Even the two case studies involving existing transportation management centers had slightly different problems to address relative to work zone mobility and safety management. For the Utah I-15 CORE project case study, the key problems were:
- A lack of convenient alternate routes to rely on when lane and full roadway closures on I-15 were required, and
- The potential for congestion to develop in locations along I-15 where existing ITS infrastructure was limited or non-existent, limiting the ability of traffic operations center (TOC) personnel to respond quickly and properly to any issues that arose.
For the Las Vegas Freeway and Arterial System for Transportation (FAST) system case study, key problems included:
- Being included early enough in work zone design and scheduling decisions to help determine how best to make use of existing ITS resources (both equipment and personnel), and
- Estimating how work zone impacts in one part of the system will influence traffic operation on other parts of the system.
Specify Requirements of the Solution
The next step in the decision process is the development of well-defined requirements to compare against the strengths of various proposed alternatives. This step should occur without a pre-conceived expectation that a particular solution, such as an ITS deployment, will be used. These requirements define what a solution will do and are intended to be sure that it will meet the needs identified in the previous step. Failing to adequately specify requirements can result in a solution that is not adequate to address the actual work zone needs.
In the Illinois examples, concerns over unpredictable location, time, and extent of queues and delays led to requirements for:
- Continuous monitoring of roadway travel conditions upstream and through the project limits,
- The ability to quickly detect if a queue had formed, and
- Quick notification of the presence of a queue and delays to approaching traffic.
In the Utah Bangerter Highway case study, the requirements were for a mechanism to monitor travel times of individual vehicle movements through the project limits, and an ability to quickly determine if those travel times were above a performance specification that defined what the acceptable travel times were for the various movements.
For the two case study examples involving existing TOC infrastructure, defining the requirements of a solution differed significantly. In the I-15 Corridor Expansion (I-15 CORE) project example, requirements included a need to maximize available capacity on the key alternate route to I-15, and the enhancement of monitoring and control capabilities along I-15 in regions where such capabilities were not fully available. Conversely, for the Las Vegas FAST example, there was a need to improve coordination across agencies in the region (such as between FAST personnel and Nevada Department of Transportation (NDOT) project planning and design staff) in order to maximize the permanent ITS capabilities that already existed. A secondary requirement was a need for continuing evaluation and monitoring of conditions during work activities to develop a better understanding of how travel patterns change within the region during work operations.
Identify and Evaluate Alternatives, as Necessary
In this step, technologies and strategies that meet the defined requirements should be identified and evaluated to: 1) verify that they will accomplish what is needed, and 2) assess the implications of the alternatives based on cost and how well they will address the identified problem. Although multiple alternatives may meet the specified requirements, cost must be balanced with how well the requirements are met: alternatives may be too costly, unnecessarily robust, or provide additional secondary benefits for minimal additional cost, and a customizable system may be preferred for a unique situation versus a cheaper COTS system.
In all of the case study examples described previously, it was already apparent that ITS was the primary feasible option to address the requirements, and the identification of alternatives involved determining appropriate vendors (in the Illinois case studies) and/or technology options available (as was the situation for the other three case studies). However, it should be noted that the agencies often already had significant experiences (typically less than successful) with some possible alternatives and had already excluded them from consideration. Two of the challenges that exist in evaluating alternatives are the uncertainties in how traffic conditions will actually be impacted during a project, and how each alternative will be able to mitigate the impacts. Consequently, this step and the following one often must rely on past experiences and engineering judgment.
Select, Design, and Implement the Best Solution
Selection, design, and implementation of the best solution will be dictated in large part by the alternative selected and the procurement method being used. Agency processes regarding permanent ITS selection, design, and implementation in most regions have evolved over time and are fairly well established and are guided by an ITS Architecture. However, this is often less so for work zone-specific solutions. Agencies must balance the need for specificity in their desired solutions to allow fair competition among vendors, but must guard against over-specifying the solution, which has the effect of limiting available competitors.
With regards to work zone ITS solutions, the case studies have demonstrated that it is important to include ITS device maintenance as a condition in the contract, in order to keep the contractor engaged in maintaining device operability throughout the project. The case studies have also shown that the benefit of providing drivers with real-time information is greatest during the first days of the roadwork activity and subsequent phase changes. This makes it important to have an adequate testing period prior to the start of monitoring and performance assessment to validate system operation and develop confidence in and ensure accuracy of the values being generated.
The final step in the decision process should be an evaluation of how the selected solution met the requirements and addressed the problems initially identified. Agencies gain experience and insight with each deployment, and formally incorporating this learning process into future decisions is enhanced through a proper evaluation and documentation effort. This does not imply that the effort needs to be extensive or exhaustive, however.
From the perspective of work zone ITS solutions, it is apparent that a good data archival structure is important to have to facilitate quick and accurate analysis of work zone impacts that have occurred. The Utah Bangerter Highway case study illustrated that performance-based specifications require significant evaluation to ensure accurate enforcement of penalties. While it is not necessarily important to monitor every movement in a performance-based specification, a mechanism must be established to document non-construction events that cause delays as they occur.< Previous | Next >