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1 Summary In the United States, between 2010 and 2018, an average of 679 people died and about 36,750 people were injured each year as a result of motor vehicle crashes in work zones (National Work Zone Safety Information Clearinghouse). It is also estimated that work zones account for nearly 24% of nonrecurring traffic delays. Reducing these crashes and traffic delaysâand their negative effects on lives and the economyârequires a better understanding of the effectiveness of work zone transportation management strategies. Transportation management plans (TMPs) are a set of coordinated strategies designed to help agencies achieve their work zone projects goals related to traffic mobility, efficient system operation, motorists and workers safety, and other operational targets. State Departments of Transportation (DOTs) and other transportation agencies currently develop and implement TMPs, which typically involve coordinated strategies related to temporary traffic control (TTC), transportation operations (TO), and public information. TMPs also help road users traverse work zones safely by understanding project effects, alternatives, scheduling, and anticipated benefits. State DOT practices, however, vary considerably with respect to what the agency considers when selecting strategies to integrate into a TMP. Additionally, practitioners can be uncertain of the effectiveness of their strategies and the value of their economic benefit. As a result, transportation agencies may not fully understand the application, safety/operational effectiveness, or the cost-efficiency of their TMP decisions. The objectives of this project, NCHRP 03-111: Effectiveness of Work Zone TMP Strategies, are: â¢ Provide information on a wide range of strategies for work zone practitioners in the form of a âGuidebook.â â¢ Conduct field evaluations of three selected TMP strategies: truck lane restrictions, ramp metering, and reversible lanes. The guidebook is published as NCHRP Research Report 945 and is available on the TRB website. The guidebook provides a compendium of current knowledge on work zone strategies, including suggestions on when to use each and its benefits, effectiveness, related technical issues, design requirements, state of the practice, and cost. This report focuses on the field evaluation portion of the project, results of which are discussed below.
2 Truck Lane Restrictions. A field evaluation of the effectiveness of work zone truck lane restrictions (TRUCKS USE LEFT LANE) was conducted at three work zone sites in Michigan. â¢ Truck use of the left lane for all sites combined increased by 234.96% while decreasing by 59.36% in the right lane. â¢ Average passenger car and truck speeds showed mixed results with increases and decreases at each test site. However, across the three study sites, the overall average truck speeds reduced by approximately 3 mph (5%) with the truck lane restrictions. â¢ The comparisons of the headways of vehicles on the left lane (lane trucks were restricted to) of the freeway during with and without conditions improved. Lower headways (less than 300 feet) improved between 19% and 66%. â¢ Headways of truck following a car or truck increased on the left lane (the lane trucks were restricted to). Conditions most appropriate for truck lane restrictions are roadways with two or more lanes in each direction and interchanges spaced more than two miles apart with low ramp volumes and truck percentages between 10% and 25% of the total main line traffic stream. Ramp Metering. The effectiveness this strategy was evaluated at two work zone sites in the first full-scale deployment of work zone ramp metering in the United States. Two ramp metering scenarios were implemented during the study periodâfixed- and variable-cycle lengths. The evaluation found ramp metering had a positive effect on the following: â¢ Vehicle speeds on the mainline. Overall, under saturated conditions, fixed-cycle length ramp metering performed slightly better than variable-cycle length ramp metering with speeds increasing 8.6 mph and 5.18 mph, respectively, when compared to baseline conditions. When the mainline was less than 80% saturated, variable-cycle length ramp metering performed better than fixed-cycle length ramp metering. In each scenario, the left lane showed the larger increase as fewer vehicles attempted to merge laterally. â¢ Vehicle travel times. Fixed-cycle length ramp metering performed slightly better than variable-cycle length ramp metering with travel time improvements greater than 20%. When the mainline is less than 80% saturated, variable-cycle length ramp metering performed better than fixed-cycle length ramp metering with travel time improvement in excess of 60%. â¢ Ramp metering did not consistently affect vehicle headways at the merging areas of ramps and the mainline. The minimum average headway was 2.4 seconds.
3 â¢ Driver compliance rates for fixed and variable-length ramp metering ranged between 60% and 90% respectfully, absent any type of enforcement. â¢ A critical design feature for ramp metering is to set the ramp metering to begin at least 15â30 minutes prior to the time of saturation. Traditional ramp metering-design volume criteria cannot accommodate work zone conditions. â¢ Recommended total lane/ramp vehicles should not be greater than 1,600 vehicles per hour (ramp volumes should not exceed 400â600 vehicles per hour). â¢ For maximum effectiveness, traffic volumes should be close to 1,400 combined vehicles per hour per lane (vphpl), with ramp volumes below 600 vphpl. Reversible Lanes. The effectiveness of using reversible lanes as a work zone strategy was evaluated at three sitesâtwo in Michigan and another in Minnesota: â¢ Vehicle speeds on the mainline were generally maintained across all test sites. â¢ Travel times were shorter. The t-test results indicated using reversible lanes decreased travel time for most of the time periods analyzed. On average, travel time improved across all sites ranged between 5.6% and 15%. â¢ On occasion, vehicle headways in the reversible lane configuration decreased because of increase in traffic volumes; however, the minimum average headway was 2.7 seconds. â¢ Key to a successful reversible lane operation is understanding the traffic flow pattern, daily and weekday and knowing when to change over the lanes. Operation must be flexible enough to adjust to changes in demand. â¢ The reversible lane does not carry less traffic than other lanes as previously thought, with a maximum traffic flow per lane from 1,600 to 2,250 vphpl. â¢ The capacity reduction factor for reversible lane operation appears to be 0.90 to 1.20, the latter occurring in cases where the reversible lane operation is within barriers and not affected by ramps and other merging traffic. â¢ The number of crashes were higher when compared to a non-work zone condition, but less than expected for a work zone condition. Advanced signs and pavement markings on the approach to the taper will improve the safety/operation of the reversible lane.