Institute for Transportation

About the research

This study examined the effect of lane drop arrows on lane distributions, vehicle speeds, and vehicle conflicts at a long-term work zone in Missouri. The arrows were primarily intended to reduce traffic speeds, speed variability, and the percentage of vehicles in the closed lane. The data analysis examined the difference in the parameters before and after the lane drop arrows were installed. The primary measures of effectiveness were lane distributions, speed mean, and speed variance; however, other parameters were also studied for significance in the evaluation of the traffic control devices. For the before and after studies, the analysis took into consideration the effects of time of day and class of vehicle.

The lane drop arrows were associated with improved lane distributions at Sites 3 and 4 during the day. In general, the arrows were associated with improved mean, 85th percentile, and mean speeds of the fastest 15% of vehicles. The standard deviation of speed apparently improved in the daytime when the arrows were in place.

Vendor: Advanced Traffic Markings

About the research

This study examined the effect of rumble strips on lane distributions, vehicle speeds, and vehicle conflicts at a long-term work zone in Missouri. The rumble strips were primarily intended to reduce the percentage of vehicles in the closed lane, traffic speeds, and speed variability. The data analysis examined the difference in the parameters before and after the devices were installed. The primary measures of effectiveness were lane distributions, speed mean, and speed variance; however, other parameters were also studied for significance in the evaluation of the traffic control devices. For the before and after studies, the analysis took into consideration the effects of time of day and class of vehicle.

The rumble strips were associated with improved lane distribution at the beginning of the lane drop during both the day and night. The mean, 85th percentile, and mean speeds of the fastest 15% of vehicles all showed improvement with the rumble strips in place. The only negative change in traffic flow characteristics associated with the rumble strips was a tendency for increased speed variance, exhibited in some of the observations through an increase in the standard deviation of speed and a decrease in the percentage of vehicles within the 10-mph pace.

The study also examined the ease of installation and removal and the durability of the rumble strips. Installation required approximately 3.5 hours for a two-person team, including temporary lane closures for both lanes, while removal required approximately 2.0 hours. In general, the rumble strips maintained their structural integrity under eight days of traffic, with about 14,600 vehicles per day, including 25.6% vehicles with three or more axles. The first, failed installation attempt indicated that installing the rumble strips on possibly damp pavement without the use of a 200-lb roller can result in nearly immediate failure. The second, successful installation indicated that the rumble strips can adhere well when applied to dry pavement with a 200-lb roller.

Finally, the study examined the safety of the rumble strips. No adverse effect on traffic safety was found.

Vendor: Advanced Traffic Markings

About the research

Based on the results of this study, a recorded CB message near the beginning of a lane closure on an interstate highway work zone can be expected to be heard and understood by a high proportion of truck drivers. There is strong evidence that truck drivers appreciate the warning and will adjust their lane choice based on the warning. The effect of the warning on speed and speed variance is less certain. There may be some beneficial effect on speed and speed variance near the beginning of the lane closure, but the results are inconclusive.

The primary costs of the CB Wizard Alert System include the system itself and staff time for installation, recording the message, and removal. No lane closures are required as the system is installed, operated, and removed without traffic disruption.

Vendor: Highway Technologies, Inc.

About the research

This study examined the effect of rumble strips on traffic speeds along the northbound and southbound directions of US 65 in Springfield, Missouri. The results indicate that the rumble strips can be placed in a reasonable amount of time and can remain visible and attached to the pavement for several months. However, the desired reductions in speed and speed variability did not occur. The rumble strips should not be expected to reduce speed or speed variability on multilane highway work zones.

About the research

Improving freeway work zone traffic control could lead to more efficient traffic flow and greater safety to workers and the driving public. Newer technologies are being developed for improving work zone traffic control as in the case of dynamic speed advisory systems. Such systems have the potential to warn drivers of slow downs near work zones and streamline traffic approaching the work zone. An evaluation of a particular speed advisory system was conducted using multiple performance measures on I-70 in St. Louis, Missouri. The use of mean speed, speed variance, and driver surveys show that the system helped to improve the safety of the work zone. Data also show that static and dynamic operations of the system produced different effects on the traffic pattern. Time headways and conflict video were collected but were not useful in this particular evaluation.

About the research

Improving safety at nighttime work zones is important because of the extra visibility concerns. The deployment of sequential lights is an innovative method for improving driver recognition of lane closures and work zone tapers. Sequential lights are wireless warning lights that flash in a sequence to clearly delineate the taper at work zones. The effectiveness of sequential lights was investigated using controlled field studies. Traffic parameters were collected at the same field site with and without the deployment of sequential lights. Three surrogate performance measures were used to determine the impact of sequential lights on safety. These measures were the speeds of approaching vehicles, the number of late taper merges and the locations where vehicles merged into open lane from the closed lane. In addition, an economic analysis was conducted to monetize the benefits and costs of deploying sequential lights at nighttime work zones. The results of this study indicates that sequential warning lights had a net positive effect in reducing the speeds of approaching vehicles, enhancing driver compliance, and preventing passenger cars, trucks and vehicles at rural work zones from late taper merges. Statistically significant decreases of 2.21 mph mean speed and 1 mph 85% speed resulted with sequential lights. The shift in the cumulative speed distributions to the left (i.e. speed decrease) was also found to be statistically significant using the Mann-Whitney and Kolmogorov-Smirnov tests. But a statistically significant increase of 0.91 mph in the speed standard deviation also resulted with sequential lights. With sequential lights, the percentage of vehicles that merged earlier increased from 53.49% to 65.36%. A benefit-cost ratio of around 5 or 10 resulted from this analysis of Missouri nighttime work zones and historical crash data. The two different benefit-cost ratios reflect two different ways of computing labor costs.

About the research

Incentive/disincentive clauses (I/D) are designed to award payments to contractors if they complete work ahead of schedule and to deduct payments if they exceed the completion time. A previously unanswered question is, “Did the costs of the actual work zone impacts that were avoided justify the incentives paid?” This report answers that question affirmatively based on an evaluation of 20 I/D projects in Missouri from 2008 to 2011. Road user costs (RUC) were used to quantify work zone impacts and included travel delays, vehicle operating costs, and crash costs. These were computed using work zone traffic conditions for partial-closure projects and detour volumes and routes for full-closure projects. Conditions during construction were compared to after construction. Crash costs were computed using Highway Safety Manual methodology. Safety Performance Functions produced annual crash frequencies that were translated into crash cost savings. In considering an average project, the percentage of RUC savings was around 13% of the total contract amount, or $444,389 of $3,464,620. The net RUC savings produced was around $7.2 million after subtracting the approximately $1.7 million paid in incentives. In other words, for every dollar paid in incentives, approximately 5.3 dollars of RUC savings resulted. I/D provisions were very successful in saving RUC for projects with full-closure, projects in urban areas, and emergency projects. Rural, non-emergency projects successfully saved RUC but not at the same level as other projects. The I/D contracts were also compared to all Missouri Department of Transportation contracts for the same time period. The results show that I/D projects had a higher on-time completion percentage and a higher number of bids per call than average projects. But I/D projects resulted in 4.52% higher deviation from programmed costs and possibly more changes made after the award. A survey of state transportation departments and contractors showed that both agreed to the same issues that affect the success of I/D contracts. Legal analysis suggests that liquidated damages is preferred to disincentives, since enforceability of disincentives may be an issue. Overall, in terms of work zone impact mitigation, I/D contracts are very effective at a relatively low cost.

About the research

Ramp metering has been successfully implemented in many states to improve traffic operations on freeways. Studies have documented the positive mobility and safety benefits of ramp metering. However, there have been no studies on the use of ramp metering for work zones. This report documents the results from the first deployment of temporary ramp meters in work zones in the United States. Temporary ramp meters were deployed at seven urban short-term work zones in Missouri. Safety measures such as driver compliance, merging behavior, and speed differentials were extracted from video-based field data. Mobility analysis was conducted using a calibrated simulation model and the total delays were obtained for under capacity, at capacity, and over capacity conditions. This evaluation suggests that temporary ramp meters should only be deployed at work zone locations where there is potential for congestion and turned on only during above-capacity conditions. The compliance analysis showed that non-compliance could be a major safety issue in the deployment of temporary ramp meters for under-capacity conditions. The use of a three-section instead of a traditional two-section signal head used for permanent ramp metering produced significantly higher compliance rates. Ramp metering decreased ramp platoons by increasing the percentage of single-vehicle merges to over 70% from under 50%. The accepted-merge-headway results were not statistically significant even though a slight shift towards longer headways was found with the use of ramp meters. Mobility analysis revealed that ramp metering produced delay savings for both mainline and ramp vehicles for work zones operating above capacity. On average a 24% decrease in total delay (mainline plus ramp) at low truck percentage and a 19% decrease in delay at high truck percentage conditions resulted from ramp metering.

About the research

Variable advisory speed limit (VASL) systems could be effective at both urban and rural work zones, at both uncongested and congested sites. At uncongested urban work zones, the average speeds with VASL were lower than without VASL. But the standard deviation of speeds with VASL was higher. The increase in standard deviation may be due to the advisory nature of VASL. The speed limit compliance with VASL was about eight times greater than without VASL. At the congested sites, the VASL were effective in making drivers slow down gradually as they approached the work zone, reducing any sudden changes in speeds. Mobility-wise the use of VASL resulted in a decrease in average queue length, throughput, number of stops, and an increase in travel time. Several surrogate safety measures also demonstrated the benefits of VASL in congested work zones. VASL deployments in rural work zones resulted in reductions in mean speed, speed variance, and 85th percentile speeds downstream of the VASL sign. The study makes the following recommendations based on the case studies investigated: 1. The use of VASL is recommended for uncongested work zones to achieve better speed compliance and lower speeds. Greater enforcement of regulatory speed limits could help to decrease the standard deviation in speeds. 2. The use of VASL to complement the static speed limits in rural work zones is beneficial even if the VASL is only used to display the static speed limits. It leads to safer traffic conditions by encouraging traffic to slow down gradually and by reminding traffic of the reduced speed limit. A well-designed VASL algorithm, like the P5 algorithm developed in this study, can significantly improve the mobility and safety conditions in congested work zones. The use of simulation is recommended for optimizing the VASL algorithms before field deployment.

About the research

In the last decade, Intelligent Transportation Systems (ITS) have increasingly been deployed in work zones by state departments of transportation. Also known as smart work zone systems, they improve traffic operations and safety by providing real-time information to travelers, monitoring traffic conditions, and managing incidents. Although there have been numerous ITS deployments in work zones, a framework for evaluating the effectiveness of these deployments does not exist.

To justify the continued development and implementation of smart work zone systems, this study developed a framework to determine ITS effectiveness for specific work zone projects. The framework recommends using one or more of five performance measures: diversion rate, delay time, queue length, crash frequency, and speed. The monetary benefits and costs of ITS deployment in a work zone can then be computed using the performance measure values. Such ITS computations include additional considerations that are typically not present in standard benefit-cost computations. The proposed framework will allow for consistency in performance measures across different ITS studies thus allowing for comparisons across studies or for meta analysis. In addition, guidance on the circumstances under which ITS deployment is recommended for a work zone is provided.

The framework was illustrated using two case studies: one urban work zone on I-70 and one rural work zone on I-44, in Missouri. The goals of the two ITS deployments were different: the I-70 ITS deployment was targeted at improving mobility whereas the I-44 deployment was targeted at improving safety. For the I-70 site, only permanent ITS equipment that was already in place was used for the project and no temporary ITS equipment was deployed. The permanent DMS equipment serves multiple purposes, and it is arguable whether that cost should be attributed to the work zone project. The data collection effort for the I-70 site was very significant as portable surveillance captured the actual diversion flows to alternative routes. The benefit-cost ratio for the I-70 site was 2.1 to 1 if adjusted equipment costs were included and 6.9 to 1 without equipment costs. The safety-focused I-44 ITS deployment had an estimated benefit-cost ratio of 3.2 to 1.