Agenda - Parks and Recreation Commission - 01/12/1995

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Feb. 8, 1983 BI KEWAYS The following criteria apply to a two-way bikeway on one side of a highway bridge: a. The bikeway approach to the bridge should be by way of a separate two-way facility, for the mason explained above. b. A physical separation, capable of taking vehicle impact shall be provided to offset the adverse effects of having bicycles traveling against motor vehicle traffic. The physical separation should be designed to minim/ze the fixed-end hazards to motor vehicles and cyclists, and if the bridge is an interchange structure, to minimize sight distance restrictions at ramp intersections. Where there is a danger that the cyclist may fall onto an adjacent traffic lane, it is recommended that bikeway bridge railings or fences placed between traffic lanes and bikeways be at least 4.5 feet high, to minimize the likehhood of bicyclists falLLug over the fa/brigs. Standard bridge railing~ which are lower than 4.5 feet can be retrofitted with light-weight upper ralhngs or chain link fence, suitable to protect bicyhsts. A fence should also be provided on retaining walls when a bikeway is located close to the top of the retaivgng wall. The use of existing bridge sidewalks for bicycle traffic may be considered on exffsti~g bridges when the side- walk is of sufficient width to accommodate the cyclists. In such cases, ramps should be installed at the sidewalk approaches, if approach bikeways are two-way, the side- walk facility should also be two-way: Whenever the bridge sidewalk is utilized for a bikeway, a special effort should be made to remove obstacles that will be hazardous to b/cycle travel. Whenever bicyclists are directed from bike lanes to sidewalks, curb cuts (see Standard Plate 7056) should be flush with the street to assure that bicyclists are not subjected to the hazards of a vertical lip crossed at a flat angle. Curb cuts should be wide enough to accom- modate adults' tricycles and twowheel bicycle trailers. $. Bridges for Bikeways A bhdge designed exclusively to carry bicycles over a natural barrier or across a highway should have a minimum width of 8 feet, particularly where two-way traffic is to be accommodated. The mirfimum clear width of the bridge shal] be the paved width of the approach bike- way. If pedestrians are to use the structure, additional width is recommended. See Figure M. In the design of the bicycle overpass, all of the bicyclist's requirements with respect to grade, turning radius, width, cross slopes and speed should be consid- ered. The structure roadway should have a minimum width of 8 feet to allow adequate room for stopping and passing maneuvers. Ramp grades generally' need to be steeper than elsewhere but. preferably, should not exceed 8.5 percent; desirably, they should be in the range of 5.10 percent. See Figure M. With these grades, bike speeds wig increase on the downward movement. Precautions should be used to elirr~ate, where possible, hazards to the cyclists near the end of the ramp. The cychst should also be warned, such as by signing, of the hazards of steep grades where they do occur. Parapet barriers should be designed to provide adequate side protection. Screens, similar to the type which is provided on pedestrian overpasses, should be used where incidents of dropped objects can be expected without such protection. Where the overpass is removed from other structures, the vertical clearanos of the overpass over the roadway should be slightly higher than the minimum clearance required for vehicular structures due to the fact that bicycle structures are less resistant to impact if struck by an overhefght vehicle. Generally, 17 to 22 feet are considered desirable. The structure, approach and ap- purtenances should be designed in such a manner that ~cyclists are physically prevented from crossing the vehicular roadway at grade. Bridge railings or fences and parapets, particu- larly at the sides of spiral ramps, should be at least 4.5 feet high to minimize the l/kelihood of bicyclists falling over the sides, or being catapulted over in the event of mishap. 4. Bikeways Under Bridge Structures Figure N pro'fides acceptable locations, separations and widths for rural designs. Figure O provides these same details for urban designs. 5. Underpasses Generally, a bikeway underpass is a tess desirable method of carrying the bikeway across a major highway than an overpass structure. An underpass has the cLisad- vantages that unless it is well located and openly designed, it may be conducive to crime and vagrancy. Contrary to the above statements, there may be times when an underpass may be the most desirable alter. nato. This may occur where the grade is uniform thru the structure and for a considerable distance at both approaches to afford a better view for safety's sake. Another instance might be .when the highway to be crossed is on embankment and the cost of constructing an over- pass would be excessive. Underpasses may be constructed of cast-in-place or precast concrete box culverts, or arch-type steel or concrete pipe with the proper horizontal and vertical clearances. Of considerable concern /n conjunction with any type of bicycle underpass is the possibihty of attacks upon the bicyclist. Where an underpass is necessary, the designer should whenever possible, be selective as to location to facilitate safety. Approaches and grades should provide the mammum possible field and range of vision of the way I i I I I I I I I