Practices in One-Lane Traffic Control on a Two-Lane Rural Highway (2018)

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101 Conclusions The primary objective of this synthesis was to identify and synthesize practices and devices for establishing one-lane traffic control on rural two-lane highways. Traffic control methods dis- cussed in the MUTCD (FHWA 2009) for 1L2W operations include flagger control, flag transfer, self-managed (Stop/Yield) control, AFADs, TTCSs, and pilot car operations. In addition, several state DOTs utilize advance flagger methods. Research methods designed to achieve the synthesis objectives included a comprehensive literature review and survey questionnaire responses from members of AASHTO Subcommittee on Construction and FHWA Work Zone contacts at state DOTs. Responses from 45 state DOTs and 3 Canadian transportation organizations were received. Following the review of survey questionnaire results from responding organizations, seven organi- zations including California, Florida, Kansas, Massachusetts, Michigan, Oregon, and Rhode Island DOTs were identified for follow-up telephone interviews to obtain additional information. Results of the research are summarized in Table 5-1. Human flagger control is the most common traffic control method for 1L2W operations among state DOTs. Advance flaggers, flag transfer, and self-managed controls are not commonly utilized. Despite the safety benefits of moving flaggers further from travel lanes, AFADs are not rou- tinely used by state DOTs; however, state DOTs including Florida, Kansas, Minnesota, Missouri, Oregon, and Virginia have developed plans and guidelines for the use of AFADs. TTCSs are generally preferred over AFADs for long-term operations. For short-term operations, contrac- tors often prefer human flagger control due to initial AFAD implementation costs and setup and removal time. After flagger control, TTCSs and pilot cars are the most common traffic control methods used for 1L2W operation. TTCSs are best suited for long-term operations because continuous human interaction is not required. Pilot cars are often used to maintain vehicle speeds and guide motorists through TTC zones. Several state DOTs—including Massachusetts, Connecticut, and Rhode Island DOTs—use law enforcement to help control traffic in 1L2W operations. For example, Massachusetts con- trols traffic in 1L2W TTC zones primarily with law enforcement details. Until 2008, MassDOT was required by law to use police details in 1L2W operations. Non-law enforcement flagger control in Massachusetts was first allowed in 2008 for low-speed (less than 45 mph) and low- volume roadways. Self-managed control methods are utilized in TTC zones with short closure length and very low traffic volumes. When AFADs are used, they are often used in short-term TTC zones, and TTCSs are often utilized in long-term 1L2W operations. Pilot cars are often deployed in long and complex 1L2W TTC zones. C H A P T E R 5 Conclusions and Future Research

102 Practices in One-Lane Traffic Control on a Two-Lane Rural Highway State DOTs use different design criteria including length of closure, vehicle delay, traffic volumes, and speed for selecting traffic control methods in 1L2W operations. Often, state DOTs require justification and traffic management plans when design criteria are not met. The maximum length of closure allowed by state DOTs varies between 100 feet and 4 miles, depending on the traffic control method. Single flagger and self-managed controls have lower distance thresholds while pilot car and human flagger control (one flagger at each end) have greater distance thresholds. The maximum length of closure with TTCSs is often less than with pilot cars and human flagger control, which is primarily due to challenges with communication and excessive vehicle delay. Communication and coordination become problematic with TTCSs on long 1L2W sections, especially if there are multiple side roads or driveways with high volumes. If the length of closure is long and pre-timed signal control is used, unacceptable vehicle delays may occur. Self-managed or single flagger methods are best employed when traffic volumes are less than 2,000 vpd. Several DOTs also require the posted speed limit to be less than 45 mph when a single flagger is utilized. In state DOT guidelines, the maximum allowable vehicle delays vary between 5 and 30 minutes. Speed limit is also considered in selecting proper 1L2W methods. State DOTs often analyze capacity and vehicle delays in 1L2W TTC zones by consulting the HCM. ODOT utilizes a web-based tool to examine TTC zone traffic analysis (WZTA). The web-based WZTA tool provides lane closure restrictions and delay estimates resulting from Traffic Control Method Advantages Disadvantages Flagger Is readily available Operations are efficient Quick setup and removal Flaggers can handle irregular, emergency, or noncompliant motorist situations Flaggers are exposed to traffic Personnel management is problematic Advance Flagger Alerts drivers when sufficient sight distance is not available Additional cost Advance flagger safety concerns Flag Transfer Provides a means of communication between flaggers when other communication methods are not available Not efficient since drivers often do not return the flag to the flagger at the other end AFAD Improves human flagger safety by positioning them off the roadways Setup and removal is easier than temporary signals Cannot be used in constant, long-term operations Setup and removal time is longer than flagger control Higher initial equipment costs Additional maintenance costs Self-managed Is the least expensive method Cannot be used in long 1L2W TTC zones Cannot be used in TTC zones with high traffic volumes TTCS Suitable for long-term operations No flagger safety/management concerns Actuated signals provide efficient services Motorists are familiar with signal indications Long setup and removal times Not suitable for long TTC zones Pre-timed signals may increase delay Higher initial equipment costs Requires engineering expertise to establish efficient timing plans Required regular maintenance and malfunction inspections Coordination with side road signals is problematic Pilot Car Maintains desirable vehicle speed Suitable for TTC zones with multiple side road intersections Assists motorist through long and/or complex TTC zones Higher operation costs for driver and vehicle Controlling vehicle queue behind the pilot car is problematic Table 5-1. Advantages and disadvantages of 1L2W traffic control methods.

Conclusions and Future Research 103 construction, maintenance, utility work, or incident response. MDOT uses a software tool called CO3 to estimate the magnitude and impacts of traffic congestion during a construction project. When side roads intersect with 1L2W TTC zones, additional traffic control devices are required at the side roads. The self-managed method, flagger method, and TTCSs are frequently used for side road treatment. When traffic volumes are low, self-managed control can be effective. If traffic cannot be effectively self-managed, flaggers are utilized at side roads within the 1L2W work area. TTCSs are used at side road intersections; however, these signals need to be coordinated with signals located at both ends of 1L2W TTC zones. In some cases, pilot cars are also used to safely direct traffic through 1L2W sections when multiple side roads or driveways exist. In 1L2W TTC zones at intersections, state DOTs—including Delaware, Indiana, Oregon, and Pennsylvania—use flaggers to control traffic. The number of required flaggers and the position of the flaggers vary among the DOTs. 1L2W operations at roundabouts, TPRSs, and DADs are innovative practices used by a very small number of DOTs. Roundabout applications are included in guidelines developed by Colo- rado, Oregon, and Washington State DOTs. Typical applications utilize only flagger control. Design thresholds (e.g., maximum allowable traffic volumes on approaches), number of flag- gers to provide efficient and safe operations, and managing circulating vehicles require further investigation. TPRSs in 1L2W operations are included in typical applications by Caltrans, ODOT, KDOT, and TxDOT. The distance between the TPRSs and the flagger station varies. In addition, the conditions under which state DOTs require TPRS deployment vary. TTC devices have been used to regulate traffic at access points and driveways within 1L2W TTC zones. Ongoing experiments with DADs across the United States show that standards and guidelines applicable to all DOTs for designing and implementing the devices are needed. Future Research Suggestions for future research are as follows: • Data. Limited data are available on the safety and efficiency of 1L2W traffic control methods. Additional research is required to study the safety implications of each method when utilized under different conditions (e.g., different traffic volumes and various length of closures). • Combination of 1L2W methods. Various combinations of 1L2W traffic control methods, such as utilizing pilot cars with TTCSs or AFADs where the pilot car driver can control TTCSs or AFADs, require further investigation. • Pedestrians and bicyclists. This synthesis focused on vehicles traveling in 1L2W TTC zones and did not cover pedestrians and bicyclists. Further studies on managing pedestrians and bicyclist in 1L2W TTC zones are required. • Roundabouts. The deployment of different traffic control methods in 1L2W roundabout TTC zones needs additional investigation. Different roundabout configurations, proper design threshold, and managing circulating vehicles are topics requiring additional investigation. • DADs. Sufficient field data to evaluate the effectiveness of the devices in regulating traffic are required. Further studies on locating the devices, managing existing signs and traffic control devices, and understanding drivers’ behavior when DADs are utilized are needed.