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21 The signs give a third dimension to the usual crosswalk in this functional category have not been fully developed at striping. Speed reductions associated with slight increases in this time but were still considered as a possibility as the team driver compliance are expected with this type of treatment. developed the research plan. The four possible treatment Active-when-present flasher: This treatment looks similar categories are: to the continuous flasher; however, it is operated dynami- cally by activation of a pedestrian push button or by passive Surface alterations/rumble strips: Roadway surface alter- pedestrian detection. The dynamic push button activated ations, such as rumble strips, generate auditory cues of beacon serves to increase the conspicuity of the static pedes- approaching and/or yielding vehicles (Inman, Davis, and trian sign. The treatment typically takes the form of a flash- Sauerburger 2005). The treatment can also have the added ing beacon at the roadside, mounted overhead, or imbed- benefit of providing information on the availability of cross- ded in the pavement. able gaps. As an added benefit, the driver may be more cau- tious when approaching the crosswalk due to the additional Traffic Calming Treatments sound cue provided by the treatment. Yield-detection system: The use of in-road sensors or video Traffic calming is a method of designing streets using visual image processing to detect whether vehicles have yielded or physical cues to encourage drivers to reduce speeds. Traffic (stopped or slowly rolling) has shown promise in initial tests calming is largely self-enforcing in that the design of the road- completed under a related NIH grant (NIH 2010). An audi- way should result in the desired outcome of speed reduction. tory signal provides a speech message to the pedestrian Traffic calming can be a very effective tool for reducing the indicating when a vehicle has yielded. The functional prob- severity and frequency of crashes and even noise levels. In lems of such a system are primarily based on reliability of addition, studies suggest that drivers are more likely to yield detecting vehicles that roll very slowly, queued vehicles to pedestrians when traveling at slower speeds (Geruschat and stopped over the crosswalk (at the entry for instance), and Hassan 2005). Two possible treatment alternatives aimed at in the event of a yielded vehicle that begins moving again. reducing vehicle speeds are described below. Gap-detection system: It is possible to use in-road sensors or video image processing to detect if there is an approach- Posting lower speed (15 and 25 mph): This treatment ing vehicle (or no vehicle) within some predetermined safe considers posting regulatory reduced speed limit signs at crossing time or distance from the crosswalk. As with yield 15 mph or 25 mph. This treatment represents the lowest- detection, the use of an auditory signal via an audible device cost traffic calming treatment; however, the desired out- is imperative to provide a speech message to the pedestrian come is highly dependent on compliance of the driver. If indicating when it is safe to cross. The ability to sufficiently the design of the roundabout does not encourage slower or accurately detect such gaps at roundabouts (especially speeds (i.e., the deflection is not properly designed), then expected compliance of the posted lower speed is small the exit approach) and CTLs is not known at this time but unless heavily enforced. A lower regulatory speed limit for a is under development (NIH 2010). Yield- and gap-detection system: This treatment would CTL is impractical since it would also apply to the main line. Raised crosswalk: A raised crosswalk will reduce vehicle combine the two previous treatments to take advantage of speeds as a function of its height relative to pavement sur- the yield- and gap-detection capability that could ultimately face and the transitional slope. A low and a gently sloping be possible. It is not known at this time whether such a sys- raised crosswalk would likely have higher speeds since vehi- tem is even plausible since there has been no development cles easily maneuver over the crosswalk. Likewise, a steep of gap detection for pedestrian crossing treatments com- incline to a high raised crosswalk could result in significant pleted at this time. speed reductions; however, the reduced lane capacity may outweigh the benefit of the reduction in speed. Raised cross- Crosswalk Geometric Modification walks also introduce vertical obstructions for ambulances and snow plows that need to be considered. There is the possibility of a modified crosswalk location or an alternative crossing location at roundabouts. This approach would place all or parts of the crosswalk further away from Pedestrian Information Treatments the circulating lane to separate pedestrianvehicle interaction This category includes treatments that provide pedestri- from vehiclevehicle interaction at the roundabout. Supple- ans with audible information that can be used to make more mental treatments such as static signing, pedestrian-activated informed decisions about when to safely cross using available signs, and traffic calming techniques can all be applied in the yields and/or gaps. It should be noted that some treatments distal crosswalk situation to further enhance accessibility.