PRSR 10-12-1994 - Laserfiche WebLink

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Feb. 8, 1983 BIKEWAYS _26- The following criteria apply to a two-way bikeway Figure M. With these grades, bike speeds will increase on • on one side of a highway bridge: the downward movement. Precautions should be used to eliminate, where possible, hazards to the cyclists near the a. The bikeway approach to the bridge should be end of the ramp.The cyclist should also be warned,such as by way of a separate two-way facility, for the reason by signing, of the hazards of steep grades where they do explained above, occur. Parapet barriers should be designed to provide adequate side protection.Screens,similar to the type which b. A physical separation, capable of taking vehicle is provided on pedestrian overpasses, should be used where impact shall be provided to offset the adverse effects of incidents of dropped objects can be expected without such having bicycles traveling against motor vehicle traffic. The protection. Where the overpass is removed from other physical separation should be designed to minimize the structures, the vertical clearance of the overpass over the fixed-end hazards to motor vehicles and cyclists, and roadway should be slightly higher than the minimum if the bridge is an interchange structure, to minimize sight clearance required for vehicular structures due to the fact distance restrictions at ramp intersections. that bicycle structures are less resistant to impact if struck by an overheight vehicle. Generally, 17 to 22 feet are Where there is a danger that the cyclist may considered desirable. The structure, approach and ap- fall onto an adjacent traffic lane, it is recommended that purtenances should be designed in such a manner that bikeway bridge railings or fences placed between traffic bicyclists are physically prevented from crossing the lanes and bikeways be at least 4.5 feet high, to minimize vehicular roadway at grade. the likelihood of bicyclists falling over the railings. Standard bridge railings which are lower than 4.5 feet can Bridge railings or fences and parapets, particu- be retrofitted with light-weight upper railings or chain link larly at the sides of spiral ramps, should be at least 4.5 fence, suitable to protect bicylists. A fence should also be feet high to minimize the likelihood of bicyclists falling provided on retaining walls when a bikeway is located close over the sides, or being catapulted over in the event of to the top of the retaining wall. mishap. The use of existing bridge sidewalks for bicycle 4. Bikeways Under Bridge Structures • traffic may be considered on existing bridges when the side- walk is of sufficient width to accommodate the cyclists. Figure N provides acceptable locations,separations In such cases, ramps should be installed at the sidewalk and widths for rural designs. Figure 0 provides these same approaches. If approach bikeways are two-way, the side- details for urban designs. walk facility should also be two-way. Whenever the bridge sidewalk is utilized for a bikeway. a special effort should 5. Underpasses be made to remove obstacles that will be hazardous to bicycle travel. Whenever bicyclists are directed from bike Generally, a bikeway underpass is a less desirable lanes to sidewalks, curb cuts (see Standard Plate 7036) method of carrying the bikeway across a major highway should be flush with the street to assure that bicyclists are than an overpass structure. An underpass has the disad- not subjected to the hazards of a vertical lip crossed at a vantages that unless it is well located and openly designed, flat angle. Curb cuts should be wide enough to accom- it may be conducive to crime and vagrancy. modate adults' tricycles and twowheel bicycle trailers. 3. Bridges for Bikeways Contrary to the above statements, there may be times when an underpass may be the most desirable alter- A bridge designed exclusively to carry bicycles nate. This may occur where the grade is uniform thru over a natural barrier or across a highway should have a the structure and for a considerable distance at both minimum width of 8 feet, approaches to afford a better view for safetys sake. particularly where two-way Another instance might be when the highway to be crossed traffic is to be accommodated. The minimum clear width is on embankment and the cost of constructing an over- of the bridge shall be the paved width of the approach bike- pass would be excessive. way. If pedestrians are to use the structure, additional width is recommended. See Figure M. Underpasses may be constructed of cast-in-place or In the design of the bicycle overpass, all of the precast concrete box culverts,or arch-type steel or concrete pipe bicyclist's requirements with respect to grade, turning with the proper horizontal and vertical clearances. radius, width, cross slopes and speed should be consid Of considerable concern in conjunction with any ered. The structure roadway should have a minimum width type of bicycle underpass is the possibility of attacks upon • of 8 feet to allow adequate room for stopping and passing the bicyclist. Where an underpass is necessary, the designer maneuvers. Ramp grades generally need to be steeper than should whenever possible, be selective as to location to elsewhere but, preferably, should not exceed 8.3 percent; facilitate safety. Approaches and grades should provide desirably, they should be in the range of 5-10 percent.See the maximum possible field and range of vision of the way