Institute of Transportation Engineers. ITE Journal, May 2010 by Jackson, Jeremy
CONSTRUCTION ACTIVITY IN HIGHWAY WORK ZONES CREATES CONSTANTLY CHANGING TRAFFIC CONDITIONS THAT REQUIRE REAL-TIME TRAFFIC INFORMATION TO KEEP MOTORISTS INFORMED OF THE CONDITIONS AHEAD. SMART WORK ZONES NOT ONLY HELP INCREASE SAFETY AND MINIMIZE DELAYS, BUT THE COLLECTION OF TRAFFIC DATA CAN BE USED BY CONSTRUCTION PERSONNEL TO MAKE INFORMED DECISIONS.
INTRODUCTION
Smart work zone technology has long been an important part of work zone management, providing motorists with real-time information through variable message signs or through Web sites designed to aid travelers before they ever leave their house. The technology is constantly evolving, enabling engineers and construction personnel to actively monitor work zone operations and make important, real-time and near-real-time decisions in the field.
As part of the Oregon Transporration Investment Act (OTIA) III State Bridge Delivery Program, the Oregon Bridge Delivery Partners (OBDP), in conjunction with the Oregon Department of Transportation (ODOT), have been evaluating the use of traffic data gathered using smart work zone technology and its potential applications during a project’s design and construction phases. OBDP is a joint venture between HDR Engineering and the Fluor Corporation and is managing the repair or replacement of hundreds of bridges throughout the state of Oregon, USA, over the span of eight years.
In response to the overwhelming number of highway work zones as a result of bridge construction, ODOT has adopted a proactive policy in dealing with work zone mobility statewide. New mobility standards require that work zone traffic analysis be performed for every project that involves potential impacts to traffic flow. Work zone traffic analysis is performed at the planning stage of every project and is continually revisited throughout design and the end of construction. The use of smart work zone technology to manage mobility is an integral part of ODOTs mission to keep freight and traffic moving through an unprecedented amount of bridge construction on Oregon’s highways.
WORK ZONE TRAFFIC ANALYSIS
Work zone traffic analysis is a tool that identifies the acceptable hours of the day during which traffic lanes can be closed for construction or maintenance activities while maintaining stable and efficient traffic operations. This analysis is critical because lane closure restrictions can preserve highway safety, alleviate cosdy staging strategies and reduce lengthy travel delays. The lane closure restriction hours identified during a work zone traffic analysis are written into the project specifications for a construction project.
Preserving highway safety is the single most important goal of work zone traffic analysis. A recent report on determining the major causes of highway work zone accidents in Kansas, USA, published by the Kansas Department of Transportation and the University of Kansas Center for Research, found that 68 percent of work zone accidents were multi-vehicle crashes. These crashes included head-on, sideswipe and rear-end collisions, where 40 percent of them were caused by heavy trucks. Of these three accident types, the number of rear-end collisions in work zones can be reduced or eliminated through effective work zone traffic analysis.
Determining acceptable windows of time in which a traffic lane can be safely closed requires an estimation of traffic volumes throughout construction and a threshold for maintaining stable and efficient traffic operations. Traditional work zone traffic analysis uses up to seven manual traffic counts for day-to-day and hour-tohour differences and seasonal adjustment factors to account for month-to-month variations in traffic. An example of a weekday, Monday through Thursday, lane closure chart used to determine lane closure restriction hours is shown in Figure 1.
The resulting 24-hour, 12-month estimation of traffic volumes are compared to a free-flow threshold that represents the maximum sustainable volume that yields average travel speeds at or near free-flow conditions. Free-flow thresholds differ depending on the type of work being performed, specific operational issues such as merging or weaving segments and driver population. Traffic volume estimates that exceed the free-flow threshold are highlighted to indicate the hours of the day when a traffic lane cannot be closed during construction.
Given the variable nature of traffic patterns over the course of a construction project, work zone traffic analysis must be performed early on in the project development process and continued throughout design to the completion of construction. During the design phase, the results of the analysis can affect project staging strategies and schedule development and have the potential to change the final design
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