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39 demonstrate negative trends, the committee works to address the plan development, but implementation and monitoring of issues that promote the variation in driver behavior. The the work zone is handled by the division and contractor with changes in trends can be identified by any of the committee some coordination from the WZTC Section. The establish- participants, including the resident engineer, contractor, and ment of the Safety and Traffic Operations Committee allows even the NCSHP. Once a mitigation strategy has been imple- any affected stakeholder to voice concerns about the work zone mented, the safety and mobility of the area are monitored to and traffic control plan at any point during the construction ensure that the strategy has been effective and does not gen- project. erate more problems, such as an increase in congestion. Committee meetings allow identified issues to be presented As an example, the committee recently managed an I-40 and resolutions to be discussed because each of the stakehold- project that had no fatalities in the work zone throughout ers provides a specific focus for the work zone. Having a discus- the construction project and a decrease in the crash rate on the sion about potential solutions with all the stakeholders allows corridor during the project. The committee feels that the each partner to voice concerns that could affect their particular reduction in the crash rate can be attributed, in part, to a com- focus area. For example, a full ramp closure could eliminate bination of the proactive management of the work zone, a dangerous weave conditions on the mainline but also may higher level of law enforcement, and extensive outreach to eliminate a key access point for emergency responders to access inform the public of the project. the roadway. The ramp closure also may eliminate key access to the local municipality. The committee approach to address- ing issues yields the most effective and supported solutions. Benefits The continuous evaluation of the work zone evaluates the The Safety and Traffic Operations Committee has developed average speed and crash rates so that problem locations can be greater trust and partnership between contractors, NCDOT, identified early and addressed. The attention to observed issues and the NCSHP. Working toward a common interest of results in greater mobility and safety within the project limits improving safety for workers and motorists has strengthened and better travel time reliability on the network. The ability to the trust developed between the multiple agencies. The com- quickly assemble stakeholders, discuss options, and implement mittee provides a means to evaluate traffic management plans solutions demonstrates an effective approach to mitigating before implementation and during construction. The continu- identified issues. The specific focus of meetings also establishes ous monitoring of the work zone provides a safer work environ- trust with the stakeholders that meetings will be successful and ment and roadway. Modifications to the traffic management results will be produced. plan can be easily implemented because everyone is continu- ally involved. Additional benefits and increased efficiencies are Michigan: MDOT Work Zone experienced through targeted enforcement on areas within the Traffic Control Modeling work zone where safety issues and a higher rate of violations are observed. The Michigan DOT I-75 Ambassador Bridge Gateway Project includes the reconstruction of the I-75 and I-96 freeways, a new interchange for the Ambassador Bridge, a redesign of the Lessons Learned Ambassador Bridge Plaza, and a pedestrian bridge across I-75 The committee has seen great success on the few projects where and I-96 to connect east and west Mexicantown in southwest a traffic management plan has been implemented. The success Detroit. The Ambassador Bridge, which connects Detroit, is based on established trust between the partners and docu- Michigan, and Windsor, Ontario, Canada, is one of the busiest menting the safety and mobility of work zones. This trust is commercial bridges in the world and the largest commercial established through targeted meetings that are held only when border crossing in North America, with approximately 11 mil- needed and involve the correct stakeholders. Documenting the lion vehicles crossing the bridge each year. It is a vital inter- impacts of work zones will provide reference points for deci- national trade route and access to the bridge needed to be sions made on future traffic management plans based on well- maintained at all times during the reconstruction. I-75 also documented successful practices. serves as a critical link for trade and manufacturing in the Midwest. For Michigan's large manufacturing industry and their many suppliers along the corridor from Ohio to Ten- Analysis and Research Observations nessee, I-75 is a necessary lifeline. The process has provided a means by which all affected stake- Construction started on the I-75 Ambassador Bridge Gate- holders can provide continuous feedback concerning the effec- way Project in February 2008 and was scheduled for completion tiveness of a traffic management plan. On typical construction in fall 2009. As part of the construction, I-75 was scheduled to projects, stakeholders are involved to a certain degree during be closed for 18 months through downtown Detroit and a
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40 complete closure of the I-75/I-96 interchange was scheduled for best laid plans. For example, MDOT found that a bridge on three months. To determine the impacts of the closure and plan another segment of I-75--part of the detour route and a criti- detours and traffic management strategies, MDOT used large- cal evacuation route from downtown Detroit--had only been network microsimulation. scheduled for resurfacing but actually needed to be completely The microsimulation model was created on the Paramics reconstructed. This required freeway lane closures on a detour model software platform by a consultant. MDOT Metro Region route for 3 months. What was planned to be a short-term clo- Planning staff and Traffic and Safety staff closely coordinated sure of this bridge ended up being a long-term closure and took with the consultant to develop and implement work zone a critical link out of the system during summer 2008. In addi- mobility mitigation plans. This case study was based on inter- tion, each time a new lane closure was required, it was critical views with MDOT Metro Region staff. to maintain access for emergency vehicles and key evacuation routes. Although the network simulation model was capable of modeling each of the many possible scenarios, the process was Description not adapted to the time-consuming coordination require- This case study examines the modeling process that MDOT ments. Operations applications, in contrast to planning appli- used to evaluate the impacts and to develop work zone traffic cations, have shorter time horizons and require faster turnover control plan alternatives. The ability of MDOT to develop and shorter information feedback loops. In order for the model network microsimulation models of work zones around the to accommodate changes in the field, a contract amendment project began years before construction started, with the for the model would need to be updated, funding would need development of the Southeast Michigan Freeway Simulation to be allocated, results would need to be analyzed, and work (SEMSIM) model on the Paramics platform. SEMSIM was zone mitigation measures would need to be updated. Addi- originally developed as a tool for helping facilitate MDOT proj- tional coordination would be needed with project staff and ect funding decisions for Southeast Michigan. MDOT Metro managers to develop, review, approve, and implement mitiga- Region Planning repurposed the SEMSIM model and applied tion measures. Large-scale network microsimulation is a new it to work zone modeling of the I-75 Ambassador Bridge Gate- technology, and time and effort will be needed for the business way Project. This marked the first time that network micro- processes to adapt to this new technology. simulation had been used in an operations analysis, as opposed The microsimulation model proved to be effective in mod- to planning applications. The model also had to take into eling impacts of major freeway closures and in evaluating a account numerous other planned closures of I-75 and sur- number of work zone traffic control strategies. MDOT was rounding roads partly because of the I-75 Ambassador Bridge able to quantitatively evaluate the impacts in terms of delay on Gateway Project and partly because of other planned freeway motorists and commercial vehicles and assign costs to that and local construction projects (3). delay to measure the economic impacts of construction clo- The MDOT consultants modeled several scenarios corre- sures and the various work zone traffic control strategies. An sponding to various project stages. The scenario for the sum- evaluation of the Gateway simulation model results showed mer of 2008 was most critical because, in addition to the I-75 that the work zone mobility plan for the 90-day period during mainline closure, it included the complete closure of the the complete closure of the I-75/I-96 interchange would save I-75/I-96 interchange, as well as other scheduled project clo- about $1.63 million a day in user costs in just the a.m. and p.m. sures within the Gateway simulation network. The MDOT peak periods alone. This was an extremely conservative esti- consultants worked closely with MDOT Metro Region Engi- mate based on an assumption of $16 per hour in user costs. neering staff, Construction staff, and Traffic and Safety staff, However, as effective as the microsimulation model was in this including the Michigan Intelligent Transportation System project, without a process in place to continually update the (MITS) Center, to evaluate various alternatives for construction model based on actual conditions during construction in the closures. They eventually came up with a plan that demon- field, the model will likely become out of date on large projects strated congestion would be high, but that the plan would work during the construction phase. and could handle the projected traffic volumes. Concurrent with the modeling effort, three major efforts Construction began in February 2008, with the most critical were developed and implemented. These included incident phase occurring in summer 2008, which entailed the complete management under the direction of Metro Region Traffic and closure of the I-75/I-96 interchange. During the three months Safety and the MITS Center; the addition of real-time sensors modeled for summer 2008, MDOT found that the traffic and and travel advisories brought into operation under the MITS congestion predicted by the model was close to what MDOT was Center; and a public involvement and stakeholder outreach observing in the actual construction work zones. effort involving meetings, presentations, and the generation of Field conditions on this complex and interdependent free- feedback from major corporations in the auto, auto supplier, way network often unexpectedly changed, upending even the and logistics industries. A comprehensive public involvement
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41 program was maintained with Detroit's Mexicantown com- City of Detroit and the major state trunkline roads, thus pro- munity as well. Coordination with MDOT's Detroit Trans- viding this capability. portation Service Center (TSC) was also critical to the work Finally, the U.S. Department of Transportation (USDOT) zone mobility effort. The Detroit TSC is responsible for all the Final Rule on Work Zone Safety and Mobility requires that the other projects on the Detroit network and for responding to impacts of work zones be determined and that transportation events and other contingencies. management plans be developed to mitigate those impacts. These new rules require that planning for work zone mobility should start as early as possible, even in the project concept Background of Agency stage. These requirements and the technology for large-scale Four groups within MDOT Metro Region worked together in microsimulation were not available until just before construc- the work zone modeling for the I-75 Ambassador Bridge Gate- tion of the Gateway Project. However, this same SEMSIM/ way Project: Planning, Traffic and Safety, Construction, and the Gateway model is being repurposed for two other mega proj- Detroit TSC. Once an initial model of the closure was devel- ects, which are presently in predesign. Thus, for the first time oped, MDOT Metro Region Planning, Traffic and Safety, and ever, MDOT will be employing advanced traffic modeling Construction worked together to evaluate different construc- techniques to perform construction staging and work zone tion scenarios and, where possible, adjusted closure schedules mobility planning before design. Microsimulation will allow or construction staging to minimize the impacts of the project. MDOT to effectively determine the impacts of the work zones The MITS Center also participated in planning for the con- and test various strategies to mitigate those impacts in the most struction. Although the MITS Center was not directly involved effective ways. in work zone mobility modeling and planning, they were inte- gral to the effort through their operation of the real-time and Detailed Process and Integration Points incident management programs. The MITS Center serves as MDOT's TMC for southeast Michigan and monitors over Figure 4.2 presents an overview of the process that was used 200 mi of freeway. The MITS Center manages real-time oper- to develop the work zone traffic control model for the I-75 ations and, under the direction of Traffic and Safety, runs the Ambassador Bridge Gateway Project. MDOT Metro Region Incident Management Program. In addition to the permanent Planning, Construction, and Traffic and Safety reviewed the traffic detectors, CCTV cameras, and DMS that the MITS Cen- models that were developed of the alternatives for construction ter regularly operates, numerous portable devices were brought closures for each phase of construction and selected the closure in to assist with monitoring traffic and providing traveler infor- plans based in part on the impact of the closures on motorist mation throughout the work zone. delay and mobility. The selected plans were shared with the MITS Center before the start of construction to allow the MITS Center time to develop strategies for the operation of the Process Development system, including how to handle incident management and The process used for the work zone modeling of the I-75 provide real-time information. One of the challenges of the Ambassador Bridge Gateway Project can be attributed to three process was that, when conditions changed in the field, there factors. First was the great likelihood that shutting down I-75 was not a process available that allowed for quick updates to would adversely affect the mobility of residents in southeast the model. A process that could adjust the model for changes Michigan, manufacturing along the I-75 corridor, and inter- in the field and assist MDOT in selecting new alternatives for national trade with Canada. It was critical for MDOT to construction closures would be valuable and assist MDOT in understand the impacts of shutting down I-75 and to deter- minimizing delay and maintaining mobility. mine how to set up traffic control and detour routes in a man- This process is considerably different from the process used ner that would have the least impact on the transportation in planning applications. Traditionally, MDOT has used micro- network. simulation for environmental clearance for large capacity The second factor that drove the process was the existence improvement or expansion projects. This process involves a of the SEMSIM model that allowed MDOT to build on the much wider cross-section of the department and is much more existing network model and to develop detailed models of integrated into ongoing MDOT business processes. Timelines the work zone traffic control strategies. Unlike other planning and information feedback loops are much longer. In addition, and design applications, work zone mobility requires a system these planning applications were focused on individual proj- perspective. Closing a part of an interstate freeway would have ects and did not involve modeling the whole network. A systemic impacts on other freeways, system interchanges, and CORSIM simulation model of the Gateway Project was origi- major arterial roads. The SEMSIM model, as enhanced for the nally created in the Environmental Clearance stage of the Gateway Project, included the core freeway network in the project, but this was project-specific and did not involve the
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42 Figure 4.2. Detailed business process diagram of MDOT work zone traffic control modeling. network. The technological innovations of programs such as Types of Agencies Involved Paramics and VISSIM opened up new opportunities for net- In addition to MDOT Metro Region Planning, Traffic and work traffic analysis. Safety, Construction, Detroit TSC, and the MITS Center, the Several key integration points were identified in the MDOT process also relied on the work completed by the consulting work zone traffic control modeling process, including the team selected to do the modeling and the contractor doing the following: construction. These groups all worked well in the initial plan- ning stages for construction. However, the real challenge was · Integration between MDOT Metro Region Planning, Con- during construction, when changes to the actual construction struction, and Traffic and Safety to model impacts of con- schedule were occurring daily because of another project in the struction, select the best work zone traffic control strategies, Gateway Project's influence area and it was not feasible to and develop operational strategies; update the Paramics model. In reviewing the process, MDOT · Coordination and integration with the Detroit TSC, which recognized that it will be important in the future to develop a is responsible for other Detroit projects. Some of these were tool that will allow field engineers and technicians to change included in the simulation for the Gateway. All required the model and to try different work zone traffic control scenar- coordination of traffic plans; ios. While the microsimulation model was effective for this · Continual integration during construction between MDOT high-budget, high-impact project, which also had a long plan- engineers responsible for construction and MDOT plan- ning horizon, other projects with smaller budgets and shorter ners responsible for modeling to incorporate construction planning horizons will require a more flexible approach. Specif- changes into the model and develop new work zone traffic ically, general project scheduling and work zone mobility for control strategies; and the annual program, which has multiple simultaneous proj- · Use of existing SEMSIM Paramics network model of south- ects, will require a more flexible process and technology that eastern Michigan to repurpose it for microsimulation of will shorten the planning and implementation cycle. Presently, freeway closures. the MDOT Metro Region is looking at developing an in-house
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43 mesoscopic model that can be used for routine scheduling Lessons Learned and staging. The existence of the SEMSIM microsimulation model was crit- Organizational changes also might be considered, such as ical in allowing MDOT to perform a detailed microsimulation bringing modeling under the direct control of the users, includ- of the entire network around the I-75 Ambassador Bridge Gate- ing the MDOT Metro Region Traffic and Safety engineers way Project. By repurposing the Paramics' SEMSIM model, responsible for operational decisions. MDOT was able to accurately and cost-effectively develop and evaluate work zone traffic control strategies around the project. Types of Nonrecurring Congestion Addressed The rapidly changing conditions in the field during con- struction led to changes from the initial mitigation plans. This process addressed nonrecurring congestion caused by Because field engineers and technicians could not access the work zones for a major project like that of the 18-month clo- model used for developing work zone traffic control strategies, sure of I-75. As noted, for projects of lesser impact, a more flex- there were a few instances when construction plans changed ible approach is needed. By using microsimulation to develop but were not incorporated into the model. Problems arose detailed models of work zone traffic control, MDOT's Metro when other projects whose closures were in the area of influ- Region was able to objectively evaluate scenarios and work ence of the Gateway Project encountered changes. To address with MDOT Traffic and Safety staff and Construction staff to this challenge, MDOT Metro Region plans to test a one- select strategies that provided the most effective mobility. county mesoscopic model using DYNASMART for modeling on a future project. Although DYNASMART does not provide Performance Measures as many capabilities as Paramics, it is an easier tool to use and more suitable for in-house use by engineers and technicians The primary performance measure that MDOT used was to that will not have the time to do detailed modeling. The hope determine the overall cost to motorists based on total delay of is that an engineer or technician in a field office can use the various scenarios. The cost savings provided an effective DYNASMART to keep up with changing conditions and con- way to compare different work zone traffic control strategies tinue to refer to the model to select the best work zone traffic against each other, and the potential for monetary savings control strategies. clearly demonstrated the benefits of careful modeling and selecting the best work zone traffic control strategies. The Gate- way Project did not have many alternatives for detour routes, Analysis and Research Observations so the task was to make the only available alternative work. The Use of microsimulation models to evaluate the impact of work simulation model helped MDOT devise ways to ensure that zone traffic control strategies proved to be effective for the ini- traffic would flow on the detour routes. For example, through tial construction. However, this project revealed some weak- the simulation model, MDOT found that selective closing nesses in the process. These primarily concerned the lack of of system interchange ramps would allow them to maintain flexibility that limited the use of the Gateway Model to respond throughput on the main detour route, which was a freeway that to unexpected developments. This flexibility relates to both ran through the heart of Detroit. In addition, auto and truck the technology and the process. The modeling work was per- delay along a set of 35 specific routes was assessed to identify formed by consultants, and the MDOT contracting process mobility issues along specific pathways. The focus was on in effect on this project did not allow quick enough response maintaining regional and international truck mobility. to sudden changes. While a large-network microsimulation model is very useful for high-impact projects such as the Gate- Benefits way, there is a need for a more flexible tool for other, lower- impact closures, as well as for staging multiple projects on the The MDOT work zone traffic control modeling provided sev- system. The problem that emerged during the Gateway clo- eral benefits. It provided MDOT with a quantitative measure of sures was related to another project that was on the Gateway total delay based on a project design, as well as the ability to detour route. The planning horizon and budget for such proj- compare work zone traffic control strategies and determine ects do not permit large-scale microsimulation. An alternative options with the least delay. By associating cost with delay, approach might be a network mesoscopic model that can be MDOT was able to measure the monetary impact of different run in-house and be under the control of the operations engi- scenarios. The process also allowed the MITS Center to coor- neers who are responsible for making decisions. dinate incident and real-time management along the detour The Ambassador Bridge Gateway Project marks the first time routes, giving them advance notice of closures and projected that network microsimulation has been used in an operations traffic volumes so that they could develop operational strategies. application. This provided a valuable learning experience on