Summary

This study quantifies benefits of ITS deployments for work zone applications and also documents key lessons learned from previous experience. Agencies interested in deploying similar systems can benefit from the findings of this study. Interested agencies also can use the tips and lessons learned from the deploying agencies to advance their knowledge and to assist with planning, design, and operation of a work zone ITS deployment.

This study helps to fill a specific gap in current research by providing findings of a quantitative nature for the effects of mobile traffic monitoring and management systems. While some studies have shown benefits, they often are limited due to difficulties with data collection, difficulties in measuring effects due to timing of construction activities, and limited funding for research and evaluation.

This study produced several quantitative benefits and provided information and outcomes as anticipated. The dynamic lane merge site showed results similar to that of previous studies, while expanding on comparisons between time periods with activation and no activation. The Arkansas site provides information on the opinions and reactions of drivers as stated directly in survey responses. The findings from the sites with active diversion noticeably expand the body of knowledge regarding work zone ITS, as quantitative information on diversion rates was not abundant prior to this study. Additionally, this study provides practitioners with information on what to expect when deploying similar systems, and also provides key insights into how to design them and tie the design to the objectives for system operation.

Based on this study, several key considerations are identified that should be considered for every ITS deployment:

• The intensity of construction activities and anticipated traffic mobility and safety impacts.
• The level of demand for the area under construction.
• Availability and adequacy of alternate routes, especially when diversion is planned.
• Needed enhancements to ensure that alternate routes operate efficiently during construction (signal timing changes, minor improvement projects prior to mainline construction, etc.).
• Access to and availability of other mode choices during the construction period.

Assessing these considerations during system design and development is important to help ensure that the ITS is needed and can be used effectively, both of which are key to knowing if an ITS deployment in a particular work zone is likely to be a good investment.

Overall, the benefits from this quantitative study were positive, as shown in Table 3.

Table 3. Key Measures by Site

System Objectives	Key Performance Measures	Benefits Based on Relative Change in Measures
District of Columbia Real Time Information System
Provide delay and travel speed information, and reduce congestion by actively diverting traffic.	Traffic Diversion, Queue Lengths	3% to 90% lower observed mainline volumes (with an average of 52%) over 9 observation periods by warning motorists prior to entering the mainline, compared with similar days of the week.*
Texas Delay Monitoring System
Provide delay information, and reduce demand and congestion by actively diverting traffic.	Traffic Diversion	1% to 28% reduction in mainline traffic volume (with an average of 10% reduction) over 20 observation periods where the system actively diverted traffic during congested periods, lessening the demand for restricted mainline capacity.
Michigan Dynamic Merge System
Reduce aggressive driving and smooth traffic flow and reduce delay at merge point.	Aggressive Maneuvers	Significant reduction in forced and dangerous merges when flashers were on (by a factor of 7 for forced merges, and a factor of 3 for dangerous merges), potentially reducing the risk of rear-end and side-swipe collisions near the merge taper.
Reduce delay from aggressive passing at the merge area.	Travel Times	Increase in travel times (from an average of 4 minutes to 7 minutes) when lights were flashing due to slightly longer queues prior to merge.
Arkansas Work Zone Information System
To improve traveler safety by providing real-time information to motorists.	Survey Response to Safety-Related Questions	82% of surveyed drivers felt that the ITS system improved their ability to react to stopped or slow traffic. 49% of surveyed drivers agreed that they felt safer traveling through the work zone because of the electronic messages. 17% were neutral, 32% disagreed, and 2% did not answer.
North Carolina Delay Monitoring System
To provide delay information and reduce demand and congestion by actively diverting traffic.	Traffic Diversion	N/A – system did not fully activate.
* Reduction includes potential reduced throughput due to queues and congested conditions (likely significant for the higher end of the range).

The findings of this study are comparable to previous research for several of the sites, and go beyond previously available knowledge on benefits for others. Previous lane merge studies showed significant reductions in aggressive maneuvers at the work zone taper, similar to the findings of this study. For sites with the potential for longer queues, agencies implemented and studied the late merge system, which also showed direct benefits. The traffic monitoring systems have proven more difficult for measuring quantified benefits, as the benefits are typically indirect in that these systems generally provide enhanced information to motorists. The systems that display alternate route guidance have been implemented to a greater degree recently, including those studied for this project. The following sections outline some of the previous research and show how the findings of this study compare with other studies.

Two types of systems are identified from previous research studies for comparison. The first is the type of system that physically controls traffic conditions such as the Dynamic Lane Merge System deployed in Michigan. The second functions as a monitoring and information dissemination system that provides motorists with real-time information so that they can make informed route choice decisions, such as the systems deployed in Arkansas, North Carolina, Texas, and the District of Columbia. Both types of systems have an element of controlling traffic to improve the operational performance of the work zone.

Enforceable Merge Systems

Michigan DOT undertook several studies in the recent past to evaluate the effectiveness of the Dynamic Lane Merge System. The system merges traffic early in locations where queue spillback is at acceptable levels. MDOT cited an effectiveness range of 3,000 to 3,500 vehicles per hour for the three-to-two lane drop, and 2,000 to 3,000 vehicles per hour for the two-to-one lane drop. Queuing will occur in both of these travel conditions and is needed to warrant use of the system since queue conditions create a potential for forced merges. For the I-94 deployment¹ (three-to-two merge), the average number of aggressive maneuvers during the peak hour decreased from 2.88 to 0.55. For a two-to-one deployment on M-53 in Grand Rapids, Michigan, the average number of aggressive maneuvers decreased from 68.0 to 32.0 during the morning peak period, and decreased from 38.0 to 9.0 during the afternoon peak period. The percent reduction in aggressive maneuvers for the Michigan site in this study was higher than previous studies; however, the total number of observed aggressive maneuvers was lower.

For higher traffic locations, agencies have successfully used the Late Merge System to smooth merges at the work zone taper. The Late Merge System allows traffic to use both lanes on one approach and advises motorists via changeable message signs to take turns merging from each lane. The Minnesota Department of Transportation (MnDOT) found that upstream usage of the lane that is closed downstream increased to 60 percent at one sensor location on I-494.² While MnDOT was not able to perform a true before and after comparison (temporary traffic control conditions both with and without ITS), evaluators observed minimal queues during the course of the study. Research has shown that the late merge system is better for higher traffic levels and where the availability of queue storage is low, while the early merge system is a tool for lower demand, higher queue storage locations. However, a system of message signs and sensors that can adjust automatically between the early merge and late merge concept, as has been pilot tested in Minnesota, may be most beneficial to owner-agencies. No sites using the late merge concept were available for study during the course of this project.

Traffic Information Systems

Some agencies have tested and used mobile traffic monitoring and management systems to provide real-time information to motorists. These systems display information about work zone conditions, but also can play an important role in alleviating traffic congestion due to incidents. It is often more difficult to evaluate the benefits of these types of systems in a quantifiable way, especially for metrics such as safety. For example, a system may provide advance warning of queued conditions to reduce speed variability and the potential for rear end collisions. But, with many common limitations in evaluating crash records for safety performance, agencies may find it difficult to quantify the benefits. Such benefits are often needed to build support from decision makers to continue use of such systems.

Some systems are also designed to provide information but with direct outcomes in mind, such as to reduce speed at a work zone thereby improving the safety performance of the work zone. A Smart Work Zone Deployment Initiative study of a speed monitoring and display system found a significant reduction in speed (5 mph) near the work zone taper. Three other deployments along I-80 near Lincoln showed similar results. The study team observed a 3 to 4-mph reduction in mean speed, a 2 to 7-mph reduction in 85th percentile speed, and about 20 percent to 40 percent increase in vehicles complying with the speed limit during system deployment.³ For another study, 46 percent to 73 percent of motorists said they slowed down when they observed speed advisory messages approaching the work zone.⁴

Some studies have tested diversion around work zones based on real-time information. Some systems actively divert traffic by providing alternate route guidance to motorists, while others provide general delay information and allow motorists to make route decisions. The limitation of the latter concept is that only motorists familiar to the area are likely to divert without the specific guidance to do so (some states offer specific alternate route guidance, lessening the burden on motorists to find their own route). For areas with mainly through traffic, this concept should be considered in the design stages to ensure the intended outcome is realized. A study of the effectiveness of an Automated Work Zone Information System on Interstate 5 in California showed diversion rates of 9 percent to 12 percent based on general condition information.⁵ Similar studies in Nebraska and Kentucky showed very little diversion based on general condition information. While the traffic makeup is unknown for the sites mentioned (commuter versus through trips), specific guidance for motorists on when to divert to alternate routes should, under the appropriate conditions, have a better result. For example, a study of a North Carolina Smart Work Zone deployment found that, "...alternate route usage is increased in the range of 10 to 15 percent with the presence of a Smart Work Zone that provides specific information about delays and alternate routes."⁶ In general, practitioners in North Carolina, on average, have observed, "...some increase in usage of alternate routes," across their various deployments of work zone ITS.⁷

The results of this study are comparable to the other studies referenced herein. Additionally, this study provides further evidence of the benefits of properly planned and design work zone ITS deployments. Examining the effectiveness of these systems over extended periods of time is an area that warrants further research.

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