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1 SUMMARY Mobile operations can either move continuously along the roadway as during most striping operations, or intermittently as during a pothole patching operation. Mobile operations on two- lane roadways present unique challenges to transportation agencies, not the least of which is the highly variable conditions encountered in the field. Transportation agencies are therefore challenged with developing TTC procedures that ensure safe and effective operations under a variety of conditions. The purpose of this document is to describe the available TTC strategies currently in use, itemize the perceived hazards and practical challenges associated with implementation of those strategies, and explain how maintenance crews can adjust TTC strategies based on actual field conditions. Part 6 of the 2009 Manual on Uniform Traffic Control Devices (MUTCD) with revisions 1, 2, and 3, dated July 2022, provides standards, guidance, and options for performing mobile operations on two-lane roadways (1). In addition to this MUTCD information, some state departments of transportation (DOTs) have established supplemental state-level guidance for mobile operations in their jurisdictions. In order to explore how agencies use these options while performing mobile operations on two-lane roadways, the research team gathered and reviewed mobile operation guidance from state transportation agencies. This review revealed that: ⢠Significant differences in TTC strategies were discovered between continuously moving operations (where workers remain in work vehicles and the convoy progresses at a constant pace) and intermittent-moving operations (where workers are typically on foot, the work activity is stationary for a short period of time, and then workers move quickly to the next location). ⢠There are different definitions and agency practices for mobile operations. ⢠Traffic volumes and roadway topography appear to be key factors that dictate how mobile work operations are accomplished. Agencies generally use local knowledge and previous experiences with mobile operations on a roadway segment to determine how work can best be accomplished. Participants of a series of focus group meetings consistently cited poor driver behaviors around mobile operations as a major concern to workers, emphasizing distracted and impaired driving, excessive speeds, tailgating of the work vehicles, and rear-end collisions with truck-mounted attenuator (TMA) vehicles or with other vehicles already queued behind the work activity. When discussing challenges specific to mobile operations on two-lane roadways, participants struggled with the trade-offs between using stationary lane closures that are perceived to provide a higher level of safety and control (but are not practical or as efficient for the conditions) and using mobile TTC operations. Based on focus group findings, many agencies base their TTC decisions on their knowledge of and past experiences with deploying TTC on each specific roadway, without any formal agency policies that establish thresholds for switching strategies. There are many decision-making factors that are considered, so development of specific thresholds can be very complex.
2 The key challenge of performing work on a two-lane roadway is how to accommodate the desire of drivers to pass the work activity area. Overall, four basic methods exist to control passing maneuvers: ⢠Self-Regulated (Uncontrolled) Passing. ⢠Passing Prohibited. ⢠Right Shoulder Passing Permitted. ⢠Passing Controlled by Flagger(s). Using information and challenges obtained through the focus groups, three undesirable driver behaviors that could adversely affect safety and effectiveness of mobile operations were identified for further evaluation. These driver behaviors were the basis of a root cause analysis: ⢠Disobeying DO NOT PASS signs, ⢠Cutting between work vehicles, and ⢠Being unaware of the presence of the work operation. The research team then conducted field observations of mobile operations in use in Texas and Minnesota. Observations included measurement of vehicle queues and passing behaviors. Key findings from these field observations are: ⢠A major safety concern with two-lane mobile operations occurs when a vehicle farther back in the following queue decides to pass other following vehicles in front of them and the work operation. Several instances were observed where a vehicle farther back made a passing maneuver that created a potential collision risk with the first vehicle in the queue as their passing maneuver was initiated. ⢠The likelihood of a driver making an undesirable passing maneuver increased as the amount of time spent waiting in the following queue to pass increases. Nearly 50 percent of drivers who must wait in a moving queue for 4 minutes or longer will attempt an undesirable passing maneuver. This increases to nearly 85 percent when wait times exceed 6 minutes. ⢠Time spent following a moving queue waiting to pass a mobile operation is affected by work operation characteristics (length of convoy, operating speed), traffic volumes, and roadway topography which dictate where passing maneuvers around the mobile operation can be completed. The frequency, length, and spacing of sections where such passing cannot occur interact in complex ways with regards to the time spent in queue. Therefore, simple volume-based guidelines as to when mobile operations will create long wait times in a queue cannot be determined. As a result of these field observations, researchers created the following guidelines: ⢠Transportation agencies strive to avoid creating conditions where multiple vehicles will queue (or platoon) behind the work operation and have to remain in that queue for more than four minutes. Selecting work periods where traffic volumes are lower is recommended. ⢠If roadway and traffic conditions are such that longer elapsed times following the
3 queue are likely to occur, the work crew should be directed to plan to pull over and vacate the travel lane to allow vehicles to pass. Agency pre-planning of potential pull- off locations along a section of roadway would help work crews implement these directions. ⢠If prior experiences or analysis of a planned mobile operation on a roadway suggests that queues are likely to be created with long elapsed following times and there are not suitable locations for the work convoy to pull over to allow vehicles to pass, a stationary work zone with positive traffic control methods (e.g. flaggers, portable signals, etc.) should be considered.
