Work Zone Speed Management (2015)

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75 chapter nine COMBINATION TECHNIQUES FOR MANAGING WORK ZONE SPEED INTRODUCTION Law enforcement has been shown to be one of the most effec- tive methods for increasing speed limit compliance in work zones; however, research has also shown that the spatial and temporal effectiveness of law enforcement is limited (except in the case of automated enforcement using the point-to- point method). Several states (e.g., California, Pennsylvania, South Carolina, Texas, and Washington) use multi-officer techniques (sometimes called enforcement packs) to enhance law enforcement effectiveness, especially in extended work zones. Nevertheless, deploying large numbers of law enforce- ment officers at work zones is subject to staffing and budgetary constraints, and may conflict with other policing priorities. In addition, enforcement for rural work zones may require police personnel to travel considerable distances from their usual work locations. As a result, a number of state DOTs and researchers have searched for possible combinations of work zone speed reduction tactics whose effectiveness would be similar to what is achieved through enforcement. Many of these combinations have arisen purely through practitio- ners’ field experience and are not well documented. A few studies have formally evaluated combination treatments; these studies are summarized in this chapter. FLORIDA: MOTORIST AWARENESS SYSTEM In 2005, the Florida DOT (FDOT) developed a combination of traffic control techniques called the Motorist Awareness System (MAS) (Reddy et al. 2008). In addition to traffic control and warning devices that are part of standard MOT plans, the MAS uses PCMS, radar speed feedback signs, and regulatory speed limit signs with flashers, as shown Figure 49. Active enforcement is also a critical element of the MAS. The sys- tem is implemented on multilane facilities with posted speed limits of 55 mph or higher when work operations require a closure and workers are present. FDOT conducted a public information campaign to notify the public of the change and the need to reduce speeds in work zones. The MAS was evaluated on two segments of I-10 and I-95 in Florida. Both are four-lane divided facilities with 70 mph posted speed limits, although I-95 has three lanes in one direction at some locations. Speed studies were conducted at three locations within each work zone: prior to, in the middle, and at the end of the work zone. Speed data were collected for three scenarios: traditional MOT, MAS without police enforce- ment, and MAS with police enforcement. Data were collected for various times of the day and days of the week. Mean speed, 85th percentile speed, and characteristics of speed distribution were used in the evaluation. Mean and 85th percentile speeds were lower when MAS was used when compared with standard MOT. MAS alone reduced the average speeds by approximately 1.5 mph. MAS coupled with enforcement reduced the average speeds by about 4 to 5 mph. Variability of travel speeds was decreased with MAS at one location. Proportions of drivers exceeding the speed limit within and near the end of the work zone were substantially reduced by MAS. Augmenting MAS with enforcement further reduced the proportion of speeders. Overall, MAS was found to be effective in reducing vehicular speeds in work zones. ILLINOIS: ENFORCEMENT WITH SPEED FEEDBACK DISPLAYS Researchers from Illinois evaluated the effectiveness of multiple speed reduction measures at two work zones in Illinois (Benekohal et al. 2010; Hajbabaie et al. 2011). The speed reduction measures studied included: • Speed feedback trailer, • Passive law enforcement, • Passive law enforcement in conjunction with speed feed- back trailer, and • ASE. One work zone had moderate speeding, whereas the other had extensive speeding. Data were collected without any treatment and served as the basis for the comparisons. For the three datasets analyzed, ASE, passive law enforcement, and passive law enforcement with speed feedback trailer, reduced the mean speeds significantly (5 to 7 mph) for the general traffic stream as well as free-flowing vehicles. The three enforcement treatments also reduced the degree of speeding: speeding by more than 10 mph was almost reduced to zero and speeding by up to 10 mph was significantly reduced. At one location, the combination treatment was more effective than ASE and law enforcement alone, whereas at the second location, ASE and combination were similar and both were better than law enforcement alone. Limited effects were found for the speed feedback trailer.

FIGURE 49 Standard detail drawing for Florida Motorist Awareness System (Florida DOT).

77 VERMONT: ENFORCEMENT WITH SPEED FEEDBACK DISPLAYS In Vermont work zones, law enforcement is typically used for presence rather than active enforcement (Lee et al. 2014). Uniformed traffic officers (UTO) are police officers contracted for work zones and stationed in marked police vehicles with the blue lights flashing. The study evaluated the effectiveness of the following four treatments on interstate highways: • UTO, • Targeted police enforcement, • Radar speed feedbacks signs (RSFS), and • Combination of UTO and RSFS when work zones are active. For all the scenarios, traffic speeds were measured for at least 1 week before, during, and after their implementa- tion, allowing statistical testing of mean speeds as well as proportions of vehicles speeding. The least effective treat- ment was found to be targeted police enforcement. Although the mean speeds and percentage of speeders decreased with targeted enforcement, they remained high. UTO and RSFS were similarly effective in lowering mean speeds and per- centage speeders. Both treatments reduced the average speed to below the speed limit. When used in combination, UTO and RSFS had more impact on speeds of travelers than when only one of them was used; the proportion of speeders was small and the number exceeding the speed limit by greater than 5 mph was close to zero. OREGON: COMBINATION STRATEGIES A recent study evaluated combinations of speed limit 50 signs, PCMS, and RSFS at two work zones in Oregon (Gambatese and Zhang 2013) (Figure 50). The combination of PCMS with RSFS recorded the lowest 85th percentile speed of all the treatments at the end of the taper. The reduction in 85th per- centile speed was about 6 mph at the end of the taper. No similar significant effect was observed when the treatments were used individually. The study recommends that a PCMS be used in conjunction with a RSFS just downstream from the end of the taper, in the buffer area, and just upstream of work activity area (Figure 51). The suggested messages included: “Slow for Workers,” “Workers on Roadway,” and “Narrow Lane” (Figure 52). The spatial effect of the combination was found to be limited. Therefore, to help maintain lower speeds next to the work activity area, the study recommends using PCMS mounted on work equipment such as pavement rollers, which ordinarily remain in or just upstream of the work activ- ity area while in use. If roller-mounted PCMS are unavailable, and if sufficient space is available in the median or shoulder, Gambatese and Zhang recommend placing PCMS and RSFS at multiple locations within the work zone, such as every 0.5 mile. INDIANA: ENFORCEMENT WITH VARIABLE MESSAGE SIGN Researchers evaluated police enforcement with and without VMS displaying an enforcement message (Chen and Tarko 2013). Stationary enforcement was found to be effective. VMS used in conjunction with stationary enforcement increased the speed reduction by an additional 3.6 mph for cars and 2.7 mph for trucks. VMS with police had a significant effect on speed up to one mile downstream as opposed to one-half mile for police enforcement. The study concluded that the most cost- effective enforcement tactic consists of one stationary police vehicle at the beginning of a work zone with a VMS placed closely upstream, displaying an enforcement message. SWEDEN: CHICANES WITH ELECTRONIC SIGNAGE AND ENHANCED LANE DELINEATION A 2007 study by Nygårdhs for the Swedish National Road and Transport Research Institute explored the effects of signage and delineation enhancements at a rural freeway work zone. A double-chicane design was taken as the “conventional” equipment base case. Three enhanced versions of the chicane were explored (Nygårdhs 2007): • The same physical layout as the standard chicane, but substituting VMS for the following fixed signs: no passing, speed limit, and left lane ends. The left lane ends sign was supplemented with a VMS panel displaying an exclamation point inside a triangle, which is a standard method of highlighting miscellaneous hazards in Sweden and many other countries. The speed limit sign flashed for speeding vehicles (flashing activated at 50 km/h) (Figure 53). • Like the previous version; however, the vertical panels delineating the chicane had arrow patterns showing which way to turn, instead of using ordinary diagonal stripes on the panels (Figure 54). • Like the previous version, but supplemented by white plastic barriers in the chicane. The two arrangements using VMS without a barrier reduced speed most effectively. In a comparison test of photographs of the different arrangements, the arrangement using a white barrier was considered clearer than the others. Nevertheless, the high clarity also appeared to lead to higher speeds. Some of the speed reduction may have been attributable to novelty effects.

FIGURE 50 Oregon DOT Standard Drawing TM 880 (Pappe 2014).

79 FIGURE 51 PCMS mounted on work vehicles: night (left) and day (right) (Pappe 2014). FIGURE 52 PCMS mounted on pavement roller: night (left) and day (right) (Pappe 2014). FIGURE 53 “Conventional” upstream chicane marking from Swedish study (Nygårdhs 2007). FIGURE 54 Swedish upstream chicane marking enhanced with LED/VMS signage (Nygårdhs 2007).