I-40 in Winston Salem, North Carolina

Work Zone and System Description

Over the past several years, the North Carolina Department of Transportation (NCDOT) has undertaken several construction projects that included the deployment of ITS technologies to help mitigate the impacts to traffic. NCDOT sought to alleviate work zone issues such as back-of-queue crashes and traffic delays, which may be more likely to occur in work zones due to capacity reductions and movement of materials and trucks to and from work sites via open travel lanes.

In early 2004, NCDOT designed an ITS system for a work zone shown in Figure 6 on Interstate 40 west of Winston Salem. The goal of the ITS system was to monitor traffic conditions and improve mobility and safety through the work zone along I-40 between the NC 801/I-40 interchange in Davie County and the State Route 1101/I-40 interchange in Forsyth County. NCDOT designed the ITS system to monitor traffic conditions within and in advance of the work area from each direction. The system components included a central base station equipped with processing software and wireless communications to link the system components, 10 portable DMS remotely controlled via the central computer base station, and 10 portable traffic sensors linked to the central computer base station. NCDOT procured the system using a special provision through the prime construction contract.

Figure 6. I-40 Work Zone and Signed Alternate Routes

Based on predetermined delay and travel time thresholds, the system provided real-time delay information and, if delays exceeded 25 minutes, recommended alternate routes via DMS.

Focus of the Evaluation

The evaluation focused on key performance metrics directly related to several main objectives for the system as defined by NCDOT. The main objectives of the system were to:

• Reduce demand and congestion (by actively diverting traffic).
• Provide delay information to warn motorists of slowed traffic ahead.
• Provide pre-trip planning information to commuters and allow system monitoring by DOT personnel via a project website.
• Build public confidence in real-time traveler information.

The study team collected traffic and construction data from May 22, 2004 through July 16, 2004.

Findings

Several schedule and data issues hindered the full assessment of each hypothesis; however, an assessment of data and other information from the overall deployment uncovered useful insights that are outlined in this section and in the lessons learned below. The study team made several interesting observations throughout the deployment, one of which showed that the ITS system never reached its full potential as it was never fully activated to encourage diversion. The level of demand was generally lower than the threshold for full activation. Several weeks of construction occurred along the corridor prior to full implementation of the system. The traffic impacts during the time period prior to deployment may have warranted full activation for active diversion. The deployment process took NCDOT longer than expected and the system was not available during the first phases of construction. Based on the analysis, which showed some inconsistencies in the data, the study team suspects that there potentially may have been some issues with system function or data archiving. Consequently, all hypotheses were inconclusive due to limitations in the information available for analysis.

Tips and Lessons Learned

The ITS schedule needs to be linked to the construction schedule to maximize use and benefit of the system. At this site, the system was deployed after several weeks where significant traffic impacts had occurred. To achieve the maximum benefit, ITS should be operational prior to any lane restrictions.

In design and implementation of ITS for work zone applications, agencies should involve the construction contractor to the fullest extent possible. Local NCDOT representatives cited the need to involve the construction contractor to the extent that they are fully aware of goals and objectives for the system, even if the contractor is not involved in the procurement of the system.

ITS deployments for work zone applications require communications and technology experts along with traffic engineering experts. A hardware / software / communications expert should be in regular (e.g., daily) contact with a traffic engineer to ensure full system functionality and that the ultimate goals of the system are achieved. For this deployment, NCDOT engineers coordinated with vendor communications experts to deploy the system.

Implementing agencies should use verification techniques to validate the outputs of the system and refine system operating procedures as needed prior to implementation. Agencies should perform a dry run using a test data set to simulate traffic condition information to monitor the system and verify output. Agencies should also develop performance metrics prior to system implementation to establish specific means of monitoring how well the system worked during the deployment. For this deployment, observation and analysis of interim data proved difficult due to the level of effort needed to access and view preliminary data sets. Therefore, NCDOT relied on the vendor to ensure system functionality and accuracy.

Personnel from the implementing agency should have real-time access to archived system data to identify any issues and monitor system functionality. A website could easily provide password protected access to the data being used by the system to make decisions. The website for this project provided access to real-time data but did not provide access to the data archives.

Deploying agency representatives should engage personnel responsible for use of supplemental components (such as NCDOT's permanent DMS for use during high delay periods) on a regular basis to ensure that everyone is current on the concept of operations and their roles and responsibilities. The North Carolina deployment relied on a portable work zone system as well as using some components of a permanent traffic management system.

Previous | Next