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Toll Facility Safety Study Report to Congress McDonald and Stammer recommend that reversible lanes not be used with ETC express lanes unless the speed of the nonstop traffic is drastically reduced. A better option may be to place the high-speed lanes on the outside (or right side) of the toll facility, but the authors suggest that this would be inconsistent with the usual design of multi-lane roadways, in which faster traffic normally uses the left lanes. McDonald and Stammer also found taper rates to be very different when comparing the transition between the roadway and the toll facility. There are two tapers, one on the approach and a second for the departure or merge. The authors suggest a modification to existing taper rate equations for the area where vehicles are anticipated to stop for toll payment. The authors suggest that at 40 mph or less, the approach taper equation should be: 2 WS L 105 where L is the minimum length of taper in feet, S is the posted speed in mph, and W is the offset distance in feet. For 45 mph or more, the approach taper equation should be: 3 L WS 8 Once vehicles have paid their toll, the authors suggest that the merge taper equation should be: 2 WS L ( 1. 5) 5W 105 for exit speeds of 40 mph or less. When speeds leaving the plaza are more than 40 mph, as in the case for ETC lanes where traffic does not stop for the toll plaza, conventional taper equations are recommended. Transition lengths include both the queue area length prior to entering the toll plaza and the recovery zone after leaving the toll plaza. Appropriate distances need to be chosen to allow vehicles to decelerate and get back up to speed when leaving the toll plaza. Transition lengths that are too short can cause conflicts and should be avoided. In general, the queue area was found to range from 75 feet to over 1000 feet and the recovery zone was found to range from 30 to 650 feet, depending on the facility. The authors state that the queue area will depend on demand, but the recovery zone should be a minimum of 75 feet in length to allow for slow deceleration of trucks. McDonald and Stammer acknowledge that lane width at the toll plaza will depend on the lane type, but they recommend that wide load lanes meet State regulations, ETC express lanes be 12 feet wide with shoulders, ETC dedicated lanes be 12 feet wide, lanes with high truck traffic (≥30 percent) be 12 feet wide, lanes with substantial truck traffic (>10 percent but
Toll Facility Safety Study Report to Congress thus urge the reader to consult the AASHTO Green Book for sight distance considerations and equations. A recent report by FHWA, conducted by Wilbur Smith Associates (2006), State of the Practice and Recommendations on Traffic Control Strategies at Toll Plazas, also provides general information on toll plaza design and traffic control devices. The report describes several recommendations dealing with safety design at toll facilities. The first section addresses design in the approach zone and recommends the use of the transition zone taper values proposed by McDonald and Stammer (see above). Additionally, the authors suggest that if an upstream interchange is located in a way that drivers cannot change lanes quickly enough to reach the ETC lanes, then the maneuver should be physically prevented through barriers. A third recommendation dealing with the approach zone is that sensors should be placed at toll lanes to prevent oversized trucks from entering the lane. The second section on safety design deals with the departure zone. The authors recommend that the transition zone taper values proposed by McDonald and Stammer be used and that recovery zones should be long enough to allow sufficient driver reorientation, acceleration, and initial merge. The authors again recommend that in departure zones, if a downstream interchange is located so close to the toll plaza that ETC users cannot safely change lanes to make the exit, then the movement should be restricted through physical barriers. The authors also suggest that when dedicated ETC lanes are used, a physical barrier should separate the dedicated lanes from other toll traffic until the other traffic has accelerated to two-thirds of the operating speed. The report addresses various other safety design issues as well, suggesting, for example, that when express lanes are used, they should be located to the far left of the plaza for consistency and that they should be designed with shoulder and lane width characteristics that are similar to the mainline approach. The report also advises the use of lighting for safety in which the intensity levels and uniformity ratios should be based on the American National Standards Institute (ANSI) and Illuminating Engineering Society (IES) values. A case study by Mohamed et al (2001) describes safety considerations related to the design of electronic toll plazas. The authors define five main lane types that are used at toll facilities (a classification similar to the one McDonald and Stammer describe) which are: manual, automatic, mixed, dedicated automatic vehicle identification (AVI), and express AVI. During a period of 3½ years from 1994 to 1997, data was analyzed for the Orlando-Orange County Expressway Authority in Florida. The data show that 32 percent of the crashes occurred at their 10 mainline toll plazas. The monthly crash rate also significantly increased when comparing the rate before ETC was added and after ETC was added (from 3.4 to 7.5 crashes per month). The authors identify several conflict points and dangerous behaviors including merging, queuing, and speeding vehicles. Some suggested reasons that ETC caused an increase in crashes could be driver unfamiliarity with the system, toll plaza configuration, and the possible speed variance between drivers that use ETC and drivers that do not. Solutions mentioned include increasing the width of the ETC lanes, arranging similar lane types within the plaza, providing more advance signing, adding variable message signs to show payment methods available and status of lanes, and an extensive use of pavement markings. Pavement markings could be used to reduce speeds, discourage weaving and lane changes, reduce driver confusion, and reduce conflict points. Appendix B – Literature Review Page B-3
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