Timed zone

Brake lights, detours, lane closures and exposed construction personnel are all common sights in roadway work areas, otherwise known as the "cone zone." Much emphasis has been placed on public campaigns to reduce speeds in the cone zone to enhance safety. These campaigns have been very successful. However, too much of a good thing is often a bad thing. Excessive construction-related congestion and low speeds create problems including lack of mobility through the work area, driver impatience and greater rear-end crash potential. Complicating things further are the ever-changing stages of construction. Therefore, collaboration with the construction team to provide cost-effective, quick-response solutions implemented in a streamlined fashion is critical.

This article presents a dynamic methodology for construction traffic management to maximize safety and minimize delays. At its core, this methodology capitalizes on state-of-the-art technology coupled with intimate collaboration. Technologies such as micro-simulation and intelligent transportation systems (ITS) can be used to assess traffic operations before and during construction, develop feasible mitigation strategies quickly and assist in incident detection and management. Collaboration among the construction team and affected stakeholders is crucial during both design and construction of the project.

Specific elements of the methodology include: (1) regular discussion with the construction team and affected stakeholders; (2) traffic data collection throughout construction; (3) travel pattern assessment and monitoring to identify potential issues, constraints and congestion points; (4) traffic operations analysis and micro-simulation; and (5) streamlined mitigation identification and implementation to alleviate congestion throughout the construction process.

Come together

Figure 1 provides an overview of the construction traffic management process. As illustrated, the traffic engineer serves as the linkage between collaboration efforts and state-of-the-art transportation technology. Maximizing safety and minimizing delay are the ultimate goals of construction traffic management; however, these goals are constrained by time and money.  Collaboration among all team members throughout the entire construction process is of the utmost importance for meeting objectives and effectively dealing with constraints. The use of state-of-the-art technologies, such as micro-simulation and ITS, facilitates quick-response, cost-effective problem solving. Collaboration and use of state-of-the-art technologies are further discussed in this article from the traffic engineer's perspective.

The ultimate effectiveness of a construction traffic management strategy is often in direct proportion to the level of collaboration achieved. The single most important component of effective, quick-response traffic management is collaboration.

Collaboration must occur throughout the process amongst a wide range of participants. The traffic engineer needs to be attuned to the real and perceived needs of the owner, contractor, construction manager, city staff, design team, transit agency, emergency service providers, bicyclists, area businesses and residents . . . the list can go on and on. To ensure success, shortcuts cannot be taken. It is critical to engage with all parties who can affect the project.

Collaboration begins on a focused level at a strategy selection meeting. This meeting involves the core internal group responsible for delivering a successful project: owner, contractor, construction manager and design team. The intent of this meeting is to describe the wide range of options available to manage construction traffic, their costs and their benefits. This core group can then collaboratively select the traffic management strategy that best responds to anticipated concerns and available budget. By matching the strategy to the project at hand, the scaleable nature of construction traffic management is capitalized on in a very real way.

It is often the case that the contractor is not involved at the early stages of project design and staging development; however, experience has revealed that their participation in the process as early as possible reaps many benefits. Rather than requiring the contractor to fit their construction process into a predetermined traffic management scheme, they can work with the team to develop a construction process and traffic management strategy that work together.  Construction phasing can be selected that responds to both the contractor's need to contain budget and the traffic engineer's need to maintain the safe and efficient flow of goods and people.

Collaboration does not end once the traffic management strategy is selected and implemented.  Ongoing internal conversations and meetings must continue to evaluate new and emerging issues and potential solutions. Meetings with staff from outside agencies and perhaps the public are needed to identify and address issues such as transit route detours, temporary pedestrian pathway needs and emergency services. The collaboration needed is most often expansive. Figure 2 illustrates a sample product, an emergency vehicle rerouting plan, of the collaborative process.

The benefits of collaboration at this level are wide-ranging. The most appropriate traffic management strategy is selected. The owner saves time and money. The contractor avoids costly delays and change orders. The design team develops cost-effective construction phasing. The construction manager identifies issues and solutions before problems arise. The traffic engineer becomes the confidant--and a broker of solutions--to all involved.

The numbers game

Data collection is an integral element of effectively managing construction traffic. However, it also can be the most costly, and the appropriate timing of data collection activities can have an impact on the overall project schedule. Fortunately, data collection is easily scaleable to fit the project at hand. For these reasons, it is critical to collaboratively identify the data to be collected and how often it will be updated.

Depending upon the issues likely to arise during construction, various types of data may be useful. The most rigorous approach is to collect all elements of data before construction begins and after each major phase of construction traffic handling is implemented. This, however, can be very costly and is often not necessary.

To assist in the selection of data to be collected and the development of a data update schedule, several data types are described below, along with discussion of the potential usefulness of each.

Field observation is an essential but often overlooked element of effective construction traffic management. Simply driving and walking a jobsite on a regular basis creates a mind's picture of conditions available to the traffic engineer at all times. Field observation can facilitate the identification of expected vehicular and non-vehicular issues to be addressed prior to construction. Visits to the site can be extremely informative in characterizing pedestrian, bicyclist and transit travel patterns, elements that are often overlooked in traditional data collection efforts. Follow-up observations during construction are essential and should be included in ongoing monitoring efforts.

Traffic counts assist in characterizing travel behavior and identifying emerging travel patterns during construction. Traffic count data may be collected at intersections or on roadway segments. A set of traffic counts collected before construction begins can serve as a baseline for comparison to conditions during construction. Periodic collection of new traffic counts during construction enables identification of potential problems even before they are fully manifested.

Origin-destination data helps to project new traveler behavior during construction. Road closures and congestion during construction often result in motorists choosing a different route. The traffic engineer can utilize origin-destination data to identify likely diversion patterns, assess potential problems and develop strategies to minimize these problems. Once again, problems can be mitigated before significant issues arise. Collection of new origin-destination data during construction is very costly and should only be considered when there are clearly significant changes in prevailing travel patterns that make the original data useless.

Travel time surveys along key routes through and adjacent to the construction zone also assist with the identification of future route choices during construction. To maximize the quality of data and minimize collection costs, travel time surveys can be conducted with Global Positioning System (GPS) units that record exact vehicle locations at one or two second intervals. During construction, travel time surveys can be useful to enable the traffic engineer to monitor issues such as emergency vehicle response times and transit route impacts.

Signal timing plans assist with the creation of an accurate traffic operations model representing current conditions. During construction, as travel patterns change and detours are implemented, one of the most cost-effective mitigation strategies is signal retiming. Having current signal timing represented within the operations model enables the traffic engineer to quickly identify, recommend and implement retiming options. When changes are made to signal timing during construction, the operations model should be updated to reflect the change, effectively becoming a database of current signal timing information.

On the lookout

Ongoing monitoring is at the heart of effective, quick-response, construction traffic management. Monitoring takes many forms including site visits, evaluation of data collected and possibly the application of state-of-the-art ITS elements.

After each change in traffic handling, vehicle, pedestrian, bicycle and transit operations should be reviewed. Frequent visits to the site by the traffic engineer allow for identification of new, unexpected issues. Visits should occur during morning, evening and off-peak times to ascertain what problems might exist.

Evaluation of the data collected to identify emerging travel patterns and issues is an important element of minimizing or eliminating problems before they become onerous. Traffic data can help identify which routes are most heavily used and can be used to update the traffic operations model for the current construction stage to facilitate quick-response problem resolution.

ITS can be incorporated into the monitoring process using traffic monitoring stations (TMS) and closed-circuit television (CCTV). These ITS technologies can detect vehicles, using both intrusive and non-intrusive methods, as well as determine travel speeds, volumes and queue lengths. These capabilities can assist in the identification of traffic problems. CCTV also can be used to visually locate and assess problems as they arise.

Properly analyzed

Analysis of traffic operations is often needed to identify the best solution to anticipated or emerging issues. There are many choices for the type of analysis and the tools utilized. The best option for the situation at hand should be cost-effective and capable of developing quick-response solutions.

Operations may be tested using various traffic operations models, ranging from those that analyze intersections independently to those that account for the interaction between intersections to high-end simulation software. Software available today, to name a few, includes Highway Capacity Software, developed by McTrans; Synchro, developed by Trafficware; TSIS (CORSIM), developed by the Federal Highway Administration; and VISSIM, developed by Innovative Transportation Concepts Inc. Data input requirements typically include traffic volumes, intersection geometrics and signal phasing. More advanced software accounts for the interaction between closely spaced intersections through the use of signal timing plans.

VISSIM is particularly useful when public consensus is desired, because it provides elaborate graphics. VISSIM allows for incorporation of bicyclists, pedestrians and transit vehicles into the operations analysis. This high-end simulation software also is capable of performing dynamic assignment in order to estimate vehicle rerouting during heavy congestion periods. Figure 4 provides two examples of traffic operations models using the VISSIM software package.

The cost to utilize each software package increases with the capability for detailed graphical representation and for operational complexities. The appropriate tool should be chosen given the funds and time available, as well as the specific needs of the project.

When the use of a traffic operations model is deemed appropriate, the model should be created and calibrated to existing conditions. Before construction begins, the model should be used to assess each phase of construction and test mitigation measures. During construction, field observations may indicate the need for new mitigation measures because of emerging issues. Because the traffic model already exists, new measures can be tested and implemented quickly.

Mitigation measures can be established before construction begins by assessing operations for each stage of construction using a traffic operations model. Mitigation measures that minimize vehicle delay and maximize safety should be established and tested both before and during construction.

Mitigation may include the use of ITS, such as a CMS, to alert motorists of upcoming construction activities, incidents downstream, recommended rerouting and roadway closures. A project website and regular communication with local media representatives also are useful methods for disseminating information to the public.

A steady balance

The assignment of managing traffic during construction tests an engineer's ingenuity. A balance between schedule and budget and between efficient traffic operations and safety must be sought. Too much of the first may result in too little of the second. A healthy level of collaboration must be achieved at the onset of the project and maintained throughout construction. Appropriate technology must be chosen to assist in data collection, traffic operations assessment and monitoring. Similarly, a balance between these two must be reached. Collaboration is of little use to the traffic engineer if the proper tools are not available to identify project impacts and test various mitigation measures. Likewise, the use of state-of-the-art traffic operations software is of little use if the traffic engineer does not have the opportunity to communicate the findings with the project team and implement field changes quickly. 

An appropriate balance between the various elements presented in this article cultivates a dynamic process that allows for flexibility and ensures cost-effective, quick-response solutions to be obtained and implemented in a streamlined fashion.