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5 Existing MUTCD Guidelines The Manual on Uniform Traffic Control Devices (MUTCD; FHWA 2009) uses work dura- tion as a major factor in TTC strategy decision making and defines five distinct durations in Section 6G.02: A. Long-term stationary is work that occupies a location more than 3 days. B. Intermediate-term stationary is work that occupies a location more than one daylight period up to 3 days, or nighttime work lasting more than 1 hour. C. Short-term stationary is daytime work that occupies a location for more than 1 hour within a single daylight period. D. Short duration is work that occupies a location up to 1 hour. E. Mobile is work that moves intermittently or continuously. Independent of the exact definitions used for short duration and mobile operations, these types of activities are inherently different from other types of stationary operations that take more time to perform. At most stationary work zones, there is ample time to install and realize the benefits from the full range of TTC devices (e.g., advance warning signs, channelizing devices, arrow panels). However, some maintenance operations only take a few minutes to complete, so the time to install and remove TTC devices can take much longer than the actual work activity itself. The MUTCD recognizes this issue and acknowledges that workers face hazards during the installation and removal of traffic control devices. Research shows that there is evidence to suggest that the installation and removal of TTC is one of the more dangerous times for highway workers (Bryden et al. 2000; Schrock et al. 2004). The MUTCD also notes that because the work time is short, delays affecting motorists are significantly increased when additional devices are installed and removed. Another factor, often forgotten, is that installing TTC devices for mobile operations reduces the efficiency of the work progress and can result in reduced safety for and increased exposure risk to the traveling public. The duration definitions in the MUTCD are purposely vague to allow individual agencies to further clarify distinctions among work durations as they deem appropriate. Because of this, both disparity and overlap exist among the definitions of short duration and mobile operations among transportation agencies as well as among the specific activities associated with each type of operation (Ullman et al. 2003; NCHRP 2009). In short duration operations in a traffic lane, a merging taper with channelizing devices is required; however, the time required to set up the lane closure can exceed the time required to complete the work. Work activities that take 15 minutes or less to complete and move from location to location throughout the work period could be considered short duration operations or mobile operations that move intermittently down the road. In fact, many public transportation agencies have included a 15-minute period in some fashion in their mobile operation definition. This time period is based on the belief that a well-prepared, efficient crew can install and remove a full set of traffic control devices for a lane C H A P T E R 2 Literature Review
6 Very Short Duration Work Zone Safety for Maintenance and Other Activities closure in approximately 15 minutes using conventional methods. In essence, the selection of a 15-minute threshold implies that anytime the work activity is stopped for longer than the time it would take to install and remove a merging taper and other appropriate traffic control devices, those devices could be installed. Some transportation agencies recognize this overlap in duration definitions and are using the terms âvery short duration operationâ or âvery short duration work zoneâ to describe quick maintenance activities. The simplified control procedures for both short duration and mobile work activities would inherently apply to VSDWZs as well. A reduction in the number of TTC devices may be offset by the use of appropriate enhanced colors or markings on the work vehicles and more dominant devices, such as high-intensity rotating, flashing, oscillating, or strobe lights on work vehicles. The appropriateness of such adjustments is ultimately based on positive guidance considerations (Lunenfeld and Alexander 1990). These larger and more visible devices on a vehicle allow it to be seen farther upstream, thereby providing advance information to drivers about a downstream blockage or lane closureâinformation that normally would have been provided through the upstream warning signs and arrow panel. However, the safety of these operations need not be compromised by using fewer devices simply because the operation will frequently change locations. For example, the benefits of enhanced markings and warning lights on mobile work operations generally decrease if available sight distance to the operations is diminished due to highly rolling terrain and/or significant numbers of large trucks in the traffic stream. The MUTCD includes two TAs for mobile operations where the work to be performed is in a traffic lane. Figure 1 shows a TA for a mobile operation on a two-lane road, and Figure 2 shows a TA for a mobile operation on a multilane road. The MUTCD also states that the multilane setup in Figure 2 may be used for short duration work as well. Canadian Guidelines The Ontario Traffic Manual (OTM)âTemporary ConditionsâBook 7 (Ontario Ministry of Transportation 2014) recognizes very short duration work and defines it as âwork that occupies a fixed location for 30 minutes or less, including the time that it takes to set up and remove traffic control devices.â The guidance indicates that if worker exposure to traffic exceeds 30 minutes, then a short duration work zone could be used. Figure 3 shows just one of 30 typical layouts (TLs) found in the OTM Book 7 that can be used for VSD work in Ontario. These TLs are similar to the MUTCD TAs for mobile and short duration lane closures. A decision matrix is also included in the OTM Book 7, a sample of which is shown in Figure 4. Research Efforts Defining Work Durations In 2002, the Texas Department of Transportation (TxDOT) sponsored a 2-year project related to mobile and short duration maintenance operations (Ullman et al. 2003; Finley et al. 2003). During this project, researchers identified the potential hazards associated with mobile and short duration maintenance operations as well as the probable underlying factors. The primary categories of hazards identified were motorist behavior, motorist comprehension, worker exposure, and vehicle conflicts. Some potential solutions were field tested in real work zones. In addition, researchers found that the definitions of mobile and short duration
Literature Review 7 Figure 1. MUTCD TA 17 mobile operation on a two-lane road (FHWA 2009). main tenance operations, as well as the classification of specific operations, were inconsistent. Although the recommended changes to the existing work duration definitions were not imple- mented, the researchers found that some of the uncertainty about which operations are consid- ered mobile and which operations are considered short duration may be due to the use of the word âworkâ in the definitions. For example, a long-term stationary operation (e.g., adding new lanes to a roadway) may contain work that moves intermittently or continuously (e.g., paving). To help distinguish between the types of operations, researchers suggested that the duration be
8 Very Short Duration Work Zone Safety for Maintenance and Other Activities Figure 2. MUTCD TA 35 mobile operation on a multilane road (FHWA 2009). associated with the TTC zone instead of the work being performed. A TTC zone is an area of a roadway where the conditions are changed using TTC devices. Thus, to be considered a mobile operation, the TTC zone would have to move intermittently or continuously. If the TTC zone is stationary (independent of whether the work is moving), the operation is not considered a mobile operation. The Florida Department of Transportation (FDOT) sponsored research to evaluate TTC strategies for performing utility operations (Theiss et al. 2009). Utility companies often perform routine maintenance tasks on multilane urban arterials where the posted speed limit is 45 mph
Literature Review 9 * See Table A. Figure 3. Ontario Traffic Manual TL-22 (Ontario Ministry of Transportation 2014). or less. These activities typically take fewer than 15 minutes to complete, but were being per- formed using the setup and removal of stationary lane closures with channelizing devices. The utility companies petitioned FDOT to allow the use of a shorter (100 ft) merging taper in lieu of the longer tapers established in the MUTCD. The researchers performed field evaluations dur- ing utility work activities in Florida. The results showed that traffic conflicts increased when the merging taper was shortened from 540 ft to 100 ft. However, traffic operations improved (com- pared to the 100 ft taper condition) when these activities were performed as mobile operations
10 Very Short Duration Work Zone Safety for Maintenance and Other Activities (with intermittent stops of 15 minutes or less) with no channelizing devices and when the large utility trucks with high-intensity rotating, flashing, oscillating, or strobe lights were used to per- form the work. As a result, FDOT implemented the research findings and now allows these TTC procedures if certain conditions are met (FDOT 2015). Improving Worker Safety Several agencies have sponsored research to improve worker safety during mobile, short duration, and very short duration operations by trying to keep vehicles from cutting between work vehicles. A well-accepted idea is that having a large spacing between work convoy vehicles encourages motorists to enter in the convoy (Faulkner and Dudek 1981). In an Illinois study, researchers investigated driver behavior around moving lane closures and the effect of altering various components of current traffic control scenarios, including the number, configuration, and spacing of shadow vehicles, and the effect of various traffic control devices and sign messages (Steele and Vavrik 2010). Part of this effort sought to optimize the spacing between shadow vehicles in transition areas. If the shadow vehicles were too close together, motorists tended to stay in the closed lane longer, vacating at the last minute. If the shadow vehicles were too far apart, intrusions may have occurred. In transition areas of mobile operations on freeways, the optimal spacing was determined to be between 200 and 500 ft. Additional work vehicles may be used to maintain these small gaps. The researchers also looked at maintaining a safe buffer Figure 4. Ontario Traffic Manual decision matrix sample (Ontario Ministry of Transportation 2014).
Literature Review 11 space between workers on foot and the closest upstream truck-mounted attenuator (TMA) vehicle; they found that 100 to 150 ft was optimal to allow TMA vehicle roll-ahead distance (if struck by an errant vehicle) yet discourage lateral intrusions from motorists cutting back into the closed lane too soon and potentially hitting the workers. In addition, the researchers found that placing an additional work vehicle 50 to 100 ft downstream of the workers also discouraged vehicles from cutting back into the closed lane too soon. Another way in which agencies have tried to enhance the safety of mobile and short duration operations is through the use of truck-mounted, changeable message signs. Both TxDOT and the Wyoming Department of Transportation (WyDOT) investigated the use of this technology for situations such as communicating information to motorists about wet paint lines during striping operations and which lane to use (Sun et al. 2011), sweeping operations, when workers are on foot, or the number of work vehicles in a convoy (Ullman et al. 2009). As a result, WyDOTâs (2011) Traffic Control for Roadway Work Operations guidebook includes some of these recommendations, which are shown in Table 1. Summary Agency decisions to define work activities as either short duration or mobile have profound implications in terms of the minimum TTC requirements. In addition, TTC requirements for mobile operations may change dramatically when the work activity requires workers to be on foot outside the vehicles. In these cases, proper placement of work vehicles and managing motorist behavior around maintenance operations is critical for worker safety. Table 1. WyDOT recommended messages for maintenance work (WyDOT 2011).