The Iowa Department of Transportation (DOT) has made improving work zone (WZ) safety a high priority. Managing vehicle speeds through work zones is perceived to be an important factor in achieving this goal. A number of speed reduction techniques are currently used by transportation agencies throughout the country to control speeds and reduce speed variation at work zones. The purpose of this project is to study these and other applicable work zone speed reduction strategies. Furthermore, this research explores transportation agencies' policies regarding managing speeds in long-term, short-term, and moving work zones. This report consists of three chapters. The first chapter, a literature review, examines the current speed reduction practices at work zones and provides a review of the relevant literature. The speed control strategies reviewed in this chapter range from posting regulatory and advisory speed limit signs to using the latest radar technologies to reduce speeds at work zones. The second chapter includes a short write-up for each identified speed control technique. The write-up includes a description, the results of any field tests, the benefits and the costs of the technology or technique. To learn more about other state policies regarding work zone speed reduction and management, the Center for Transportation Research and Education conducted a survey. The survey consists of six multipart questions. The third chapter provides summaries of the response to each question.

This report summarizes and evaluates the important findings from the literature review of the studies on work zone speed control techniques. The following treatments are included in this report: 1) flagging, 2) lane width reduction, 3) law enforcement, 4) changeable message signs (CMS), 5) rumble strips, and 6) flashing beacons. The effects of the speed control treatments on speed and traffic flow are evaluated based on: A) experiences with treatment, B) effects of treatment on speed, C) effectiveness of treatment, and D) comments about treatment. A brief description of the conditions under which the treatments were applied is provided, and the speed reduction effects of each technique are discussed. A reference matrix was prepared to identify publications related to each type of speed reduction treatment used in work zones.

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.

This synthesis documents information regarding the current state of practice for work zone speed management. The report compiles data, procedures, techniques, and technical issues related to observing and comparing work zone speeds. The speed management measures have been organized into four categories: engineering, operational, enforcement, and public education and outreach. Information included in this study was acquired through a review of the literature, two surveys of state department of transportation representatives in all states, a compilation of state agency public information campaigns, and follow-up interviews with select survey respondents from several U.S. states and one Canadian province.

Variable Advisory Speed Systems (VASS) provide drivers with advanced warning regarding traffic speeds downstream to help them make better decisions. Vehicle use on highways is increasing and the need to improve highways brings increased construction of highways, which increases the need for reducing the number of traffic lanes thus reducing capacity during construction. This often causes queues at the entrance to work zones. The purpose of this study was to evaluate the effectiveness of a VASS at mitigating queues in work zone entrances.