By: Chris Pourteau; Contributing Author
At the heart of intelligent transportation systems (ITS) is the notion of getting information about the transportation network to those who need it in a timely, efficient manner.
Better-informed drivers make smarter, safer traveling decisions. Traffic-management personnel—if armed with better information about the network they’re managing—can divert traffic around incidents on the roadway, improving travel-time reliability and decreasing the likelihood of crashes.
Occasionally inattentive drivers and exposed maintenance workers make work zones particularly dangerous areas for both. Researchers at the Texas A&M Transportation Institute (TTI) completed a study for the Texas Department of Transportation (TxDOT) that looked at better coordinating information collected in work zones with regional transportation-management centers (TMCs) as a way of making work zones safer, particularly in rural areas.
They’re a little different
Many existing urban-area TMCs support work-zone operations: from detecting, monitoring and responding to incidents on the roadway to collecting information on planned or current lane closures and disseminating it to drivers via traveler-information websites, dynamic-message signs, highway advisory radio or even 5-1-1 telephone systems. In some locations, TMCs even track information for performance-monitoring purposes.
“Rural areas are different,” said TTI Research Engineer Dan Middleton, who headed up TTI’s Project 0-6427, Use of Intelligent Transportation Systems in Rural Work Zones. “Typically rural roadways have less monitoring infrastructure than urban areas. But there are new, mobile technologies that can help monitor and mitigate the effects of rural work zones on the motoring public. These technologies can also make traveling through work zones safer for motorists and workers.”
Some commercially available systems are designed with a typical, manned TMC in mind, where an operator makes decisions on how to respond to the information received and what information to share with the traveling public. Other systems operate automatically, detecting certain traffic conditions (e.g., speeds, occupancies, volumes, queue lengths) and disseminating certain information (e.g., travel times, speeds, delays) on portable changeable message signs (PCMSs), highway advisory radio or a vendor-developed website.
In both cases, the vendor usually builds the overall system using requirements specified by the highway contractor or the state DOT, then monitors the system and provides necessary maintenance support. However, there have been a few instances where state DOTs have purchased and operated their own systems. TxDOT charged TTI with determining how it could better use ITS technologies in rural work zones to benefit the Texas transportation network. Specifically, the goals of Project 0-6427 were:
Determine the state of the practice in smart work zones (SWZs) across the U.S.;
Develop an architecture to integrate work-zone ITS into existing TMCs;
Use simulation to develop proof-of-concept testing of selected ITS treatments; and
Identify new and innovative uses of ITS as applied to smart work zones.
Researchers conducted a literature review and polled TxDOT traffic managers to identify their safety and mobility needs in a work zone. They also researched the current market to determine commercially available technologies to potentially address those needs. Based on this research, Middleton and his team developed two levels of architecture for integrating work-zone ITS data using these products with a regional TMC. They also explored new uses for work-zone information and made recommendations for operating existing ITS systems in concert with SWZs.
Researchers derived the following list of justifications for choosing to use an SWZ:
Crashes due to work zone;
Excessive queuing;
Excessive delay;
Traffic volume above some minimum level;
Project length more than some value;
Traffic impact on local business, etc.; and
Site-specific issues such as sight-distance limitations.
To determine if one or a combination of these circumstances truly warrants implementing an SWZ, TTI suggests conducting a benefit-cost analysis. To determine the potential benefits of SWZs, researchers investigated implementations nationwide (see Table 1).
Decision makers also should consider another option: Choose an alternate route for traffic around the work zone. Two factors impact deciding if an alternate route is the best solution: (1) the availability of a route and (2) the ability of the route to be safe, simple and capable of handling the additional traffic volume. If an alternate route is not feasible, a DOT should consider what advantages might derive from introducing ITS into a rural work zone.
Give them options
“Since different circumstances require different solutions, we wanted to give TxDOT options,” explained Middleton. “So we came up with recommendations for integrating ITS with or without a TMC involved.”
Local work-zone functions might include operations where data collected within the work zone trigger actions defined by a traffic-management plan. For example, excessive traffic volume might trigger displaying messages on changeable message signs. (The message might involve general delay information and/or guide motorists to an alternate route.) Simpler systems might involve stand-alone architecture not requiring coordination with a TMC. More complex environments would likely require interfacing ITS data-collection equipment with a TMC. At the stand-alone level, though there is no TMC involvement, a local DOT engineer would still need to monitor the work zone. Table 2 shows both shared and differentiated characteristics for introducing ITS into a Texas work zone, whether or not a TMC is involved.
At the stand-alone level, the DOT must be able to:
Monitor the work-zone site.
o Speeds from detectors;
o Messages sent to PCMSs; and
o End-of-queue warnings.
Receive alerts or alarms indicating problems.
o Text message or other correspondence; and
o Speed reductions below thresholds.
At the integrated level, TxDOT must be able to:
Maintain full control.
o Integrate with normal TMC operation; and
o Integrate using LoneStar protocols and center-to-center (C2C) functionality.
Monitor and control the work-zone site.
o Speeds and counts from detectors;
o Notification of equipment malfunctions (optional);
o Messages sent to PCMSs;
o Alternate route (if available); and
o Real-time weather information at key locations.
Table 3 indicates some criteria for determining if a stand-alone or integrated solution is right for a given work zone.
Working conditions
Determining the conditions for justifying a SWZ began with simulations focusing on end-of-queue warning and travel-time monitoring. For queue monitoring, the research team used speed-based information to keep track of the queue status and inform drivers upstream of the approximate back-of-queue location via PCMSs.
Travel-time monitoring simulated Bluetooth technology to provide an estimate of segment travel time. Time lag in reporting data can be a problem, leading to differences in travel-time estimates that the drivers see on the PCMS versus what they actually experience. The problem worsens when the Bluetooth segment is long and the congestion location is relatively close to the beginning of the segment. To address the problem, Middleton and his team developed and tested an algorithm to improve the travel-time estimate using the real-time information from the queue-monitoring system. The algorithm significantly improved the travel-time delay estimate when the queue conditions existed (volume-to-capacity ratio > 1).
Based on TTI’s simulations for queue warning, the number of detector stations depends on the expected maximum queue length. After establishing this length for a particular work zone, determining the number of detector stations is a function of the spacing of the stations. Based on simulation results and the experience of SWZ vendors, the maximum recommended spacing is 1 mile and the desirable spacing is 1⁄2 to 3⁄4 mile.
Armed with an estimate of the maximum queue length, decision makers can then design the SWZ, which will include the number of monitoring stations on the approach to the work zone and the number of PCMSs. Based on this design, one can develop a cost estimate to buy or lease the necessary equipment for the SWZ. Once capital and operational costs are estimated, one can develop a benefit-cost analysis to justify funding the SWZ.
Researchers used “reductions in crashes expected to result from use of an SWZ” to represent the benefits side of the equation. One could also use “projected-delay reductions,” although they are usually not as critical in rural work zones. The benefits depend on:
The annual average daily traffic;
Whether the work zone is daytime or nighttime; and
The length of the zone of influence (length of queue plus length of work zone) where crashes are likely to happen as a result of the work zone.
Without relatively high traffic demand, long work zones, long queues and projects lasting longer than 1 year, conditions are not likely to meet the desired B-C criterion exceeding 1.0. For rural areas, the conditions would not be likely except on high-volume interstate highways (possibly on segments near urban areas).
Nevertheless, where opportunities exist, integrating SWZs with permanent ITS can help urban-area TMCs more effectively manage traffic by providing advance traveler information to motorists (e.g., long-haul truckers) before they enter a corridor. A rural SWZ system located on an interstate highway connecting two major urban areas could communicate critical work-zone information to the urban-area TMCs, allowing for more proactive traffic management downstream.
For example, an SWZ along the I-45 corridor could provide delay information for operators at TranStar and DalTrans, the respective TMCs in Houston and Dallas. If the delay reported by the SWZ system exceeds some predetermined threshold, TMC operators could use dynamic-message signs in their respective urban areas at strategic points to disseminate appropriate construction-related delay messages to motorists traveling in either direction on I-45. They also might use the information from the rural SWZ system to provide web-based travel-time and delay estimates for different segments along the I-45 corridor.
“Rural SWZs clearly offer substantial benefits to agencies depending on the calculated benefit-to-cost ratio,” said Middleton. “But agencies should not expect a noteworthy reduction in crashes—the most seemingly obvious benefit—without high traffic volume and long duration work zones.”
First with information
Building upon the research conducted under this project, TTI researchers are supporting TxDOT’s current I-35 Expansion Project with a first-of-its-kind traveler-information system. The construction project is expanding a 96-mile stretch of I-35 across four central Texas counties at a cost of $2.1 billion. Enhancements include widening the interstate from four to six lanes and changing frontage roads from two-way to one-way to improve safety.
On May 2, 2013, as part of its technological assistance to TxDOT on the project, TTI helped create a new end-of-queue warning system for motorists approaching nighttime interstate work-zone lane closures. The system’s main purpose is to let motorists know about a queue of stopped or slowed vehicles as they approach it.
Radar-detection devices ahead of work-zone lane closures are monitored to measure the speeds of approaching vehicles. Data from multiple sensors are analyzed and, as vehicles slow down, an algorithm triggers a message for display on PCMSs located a few miles upstream of the lane closure. As a result, motorists are warned well in advance of the slow-down as it occurs.
“This system will let motorists know how far in advance there is a slow-down,” TxDOT Director of Transportation Operations in Waco Larry Colclasure said. “It’s part of the overall effort to provide real-time information designed for motorists’ safety and the safety of the construction workers, too.”
The end-of-queue warning system is part of a larger construction traveler-information solution that also includes Bluetooth technology to help monitor traffic flow. After the I-35 Expansion Project is completed in 2015, TxDOT’s Waco District will keep this new ITS infrastructure to help manage mobility, reduce congestion and improve safety along I-35 in the district. ST
