Details:

Creators:
Click, Steven M. ; Rajagopalan, Aswini
Click, Steven M. ; Rajagopalan, Aswini Less -
Corporate Creators:
Tennessee Tech University. Department of Civil and Environmental Engineering
Corporate Contributors:
University of Arkansas. Mack-Blackwell Transportation Center ; United States. Department of Transportation. University Transportation Centers (UTC) Program
University of Arkansas. Mack-Blackwell Transportation Center ; United States. Department of Transportation. University Transportation Centers (UTC) Program Less -
Subject/TRT Terms:
[+]
Adaptive Control Green Interval (Traffic Signal Cycle) Rural Highways Rural Transportation Traffic Delays Traffic Signal Control Systems Traffic Signal Timing Traffic Simulation Variables Vehicle Miles Of Travel
Publication/ Report Number:
MBTC Project 2093:
Resource Type:
Research Paper
Geographical Coverage:
Arkansas
Corporate Publisher:
University of Arkansas. Mack-Blackwell Transportation Center
Abstract:
On April 20, 2005, the first National Traffic Signal Report Card was issued by a coalition of leading transportation organizations. This evaluation of traffic signal operations was based on input from 378 state, county, and local agencies. The overall national grade of D- clearly indicates need to address several key aspects of traffic signal operations. One key issue identified in the report: a lack of regular updates to traffic signal timing. Such poor results came as little surprise to transportation professionals. The Federal Highway Administration reports that an estimated 75% of the 260,000 traffic signals in the United States could be improved “by updating equipment or by simply adjusting and updating the timing plans.” The same report indicates that poor timing is likely responsible for “5-10% of all traffic delay or 295.8 million vehicle-hours of delay each year.” The importance of efficient traffic signal operations has increased significantly in the past two decades, as the growth of travel has greatly outpaced that of roadway capacity. From 1980 to 1998, growth in roadway capacity increased about 1% per year while travel grew by 72% . If agencies were able to provide proper traffic signal timing at all signalized intersections, estimates suggest that motorists could expect a 10 to 40% reduction in delay, up to a 10% reduction in fuel consumption, and up to a 22% reduction in harmful emissions. In addition to the poor overall national grade, the Report Card also indicated that agencies responsible for very small signal systems (< 50 signals) “scored markedly lower… than larger systems.” Virtually all rural areas will fall in this category, which averaged a full letter grade lower than their larger (i.e. suburban and urban) counterparts. The identified causes: staffing and funding. Rural agencies are unlikely to have dedicated traffic engineering staff, instead shifting traffic signal maintenance into a general public works department with little or no expertise in signal operations. Rural signals are also less likely to have dedicated funding for local or system-wide improvements, and are simply not considered candidates for the advanced upgrades which, though expensive, are becoming common in suburban and essential in urban systems. Fortunately, the continuing reduction in cost for computing capabilities has brought with it more advanced traffic signal control capabilities built into standard controllers, including many which have not yet been tested. One such feature is commonly referred to as a Variable Maximum Green Time (VMGT). This feature, provided on at least five control platforms by at least two different manufacturers, allows a local signal controller to determine if a phase failed to serve all waiting vehicles, and to adjust its length accordingly in subsequent cycles. The goal: improved traffic signal efficiency through real-time adaptation of signal timing to current conditions. The current state-of-the-practice in isolated traffic signal operations is a fixed maximum green time which terminates a phase after a given period of time. While detection systems can allow a phase to terminate early in the absence of demand, there is no mechanism to determine or adjust for unmet demand. VMGT allows for variation in the maximum green based on the presence or absence of unmet demand, essentially providing more green time in the following cycle to phases with unmet demand in the current cycle, and vise-versa. While VMGT is available on several current controllers, it is rarely used due to a lack of data on its effectiveness, an absence of guidelines for its application, and a lack of understanding of its purpose. Similar “adaptive” control strategies have been studied over complex systems of intersections with encouraging results. Reports indicate the potential for reduced delay (as much as 30%6), increased throughput, and more equitable distribution of delay. To date, most such studies have focused on large, highly complex, very costly systems for multiple intersections without considering the benefits of low cost isolated intersection techniques like VMGT. The primary objective of this proposal is to investigate the potential to improve traffic signal operating efficiency in rural areas through the use of VMGT as low cost local adaptive control. The primary measures of intersection efficiency to be investigated are average delay and intersection throughput. The primary investigative method involves HITL and CSITL simulation, which allows for computerized traffic simulations to be connected in real time with field traffic signal controller hardware, thus allowing multiple strategies to be tested with identical traffic conditions and without the difficulties of in-field traffic disruption.
Format:
PDF
Collection(s):
University Transportation Centers
Main Document Checksum:
[+]
urn:sha256:ccba785af2989470812ad1046c79f74cc0c475639de8da7ad5c5ac1172ed5885
Download URL:
https://rosap.ntl.bts.gov/view/dot/60890/dot_60890_DS1.pdf
File Type:

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