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6(2)BIKEWAYS MANUAL JUNE 17,1996 <br />c <br />c <br />c <br />c <br />c <br />c <br />c <br />c <br />c <br />c <br />c <br />c <br />t: <br />k <br />c <br />c <br />c <br />c <br />c <br />e <br />c <br />I <br />6-S.O Bicycle and Pedestrian Underpasses and Tunnels <br />A bikeway underpass may be a desirable way to carry a <br />bikeway across a highway. It has the advantages that costs are <br />generally lower than an overpass and there may be less grade <br />change for a bicyclist to negotiate than an overpass. A disad* <br />vantage is that unless it is well located and openly designed, <br />it may be conducive to crime and be avoided by bicyclists and <br />pedestrians. Providing adequate drainage may also be a <br />problem. <br />4,5 m is desirable. When the underpass is long (e.g. when go- <br />ing under a four>l^e road), wider openings are recommended <br />to improve lighting and visibility . Six meters is a desirable <br />width. Vertical clearance should at least 3 m. <br />Underpasses are usually constructed of cast>in*place or pre­ <br />cast concrete or steel in circular, arch, or rectangular shapes <br />with proper horizontal and vertical clearances. Arch shapes <br />offer good clearance and lighting. <br />The possibility of attacks upon users accompanies any <br />type of design. Be selective as to location to facilitate safety. <br />Approaches and grades should provide the ma.ximum possible <br />field and range of vision of the way ahead to the bicyclist and <br />pedestrian. Provide adequate amounts of light under struc­ <br />tures, in mnnels and at approaches. In certain cases, lighting <br />may be required on a daily. 24- hour basis. See the lighting <br />section in Chapter 5. Illuminating tunnels of a length of 10 <br />m at all times is desirable. <br />The horizontal and vertical alignments should be straight <br />for the full length and for an adequate distance on each ap­ <br />proach. The minimum width of an underpass for bicyclists <br />and pedestrians should be the paved width of the approach <br />path plus one meter. Recommended minimum width is 3.6 m; <br />Figure 6-4.0A <br />Source; IA a Octt