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52 Upper Level Lower Level FIGURE 19 Concept design of two-level signalized intersection (Shin et al. 2008). Where on-street bicycle lanes or off-street bicycle paths no more than 1:12 (must not exceed 1 in./ft), and a maximum enter an intersection, FHWA (Rodegerdts et al. 2004) advises slope on any side flares of 1:10 (United States Access Board that intersection design should accommodate the needs of 2011). Additional details of curb ramp design are also pro- cyclists in safely navigating such a large and often compli- vided in the Proposed Guidelines. cated intersection. It is recommended that geometric features to be considered include: Channelized turning lanes pose a potential risk to pedes- trians, particularly those with disabilities. Researchers on Bike lanes and bike lane transitions between through NCHRP Project 3-78 (Schroeder et al. 2011) found anec- lanes and right-turn lanes. dotal evidence that a crosswalk located in the middle of a Left-turn bike lanes. turning lane is preferable to a crosswalk at the upstream or Median refuges with a width to accommodate a bicycle: downstream portion of the turn lane. The middle crosswalk 6 ft = poor; 8 ft = satisfactory; 10 ft = good. establishes a short crossing path roughly perpendicular to the Separate facilities if no safe routes can be provided trajectory of turning vehicles (useful for establishing pedes- through the intersection itself. trian alignment), and it physically separates the conflict of turning drivers and pedestrians with the downstream merge "Curb ramps provide access between the sidewalk and point. Based on turning radii and associated design speeds, roadway for people using wheelchairs, strollers, walkers, they posited that this was the likely location where speeds of crutches, handcarts, bicycles, and also for pedestrians with right-turning vehicles would be lowest. mobility impairments who have trouble stepping up and down high curbs. Curb ramps must be installed at all inter- sections and midblock locations where pedestrian crossings Transit Considerations exist, as mandated by federal legislation," notably the 1990 Americans with Disabilities Act (ADA). According to the TCRP sponsored a recent project to develop guidance for Proposed Accessibility Guidelines for Pedestrian Facilities transit and highway agencies in the operations, planning, in the Public Right of Way, curb ramps must have a slope of and functional designs of at-grade crossings of busways in