M . Overpass
Overpasses are an important part of pedestrian and bikeway design and may be necessary to provide continuity for shared and multiuse paths . Barriers to bicycling often include freeways , complex interchanges , existing busy roads , waterways , or railroads . Overpasses and bridges should be easily accessible and convenient for pedestrian and bicycle access . Consideration should be given to cost , constructability , maintenance , aesthetics , safety , and physical constraints when designing or providing an overpass . The type of structure typically depends on the span length .
• The slope approach should grade away from the overpass to provide positive drainage away from the structure . The maximum slope approaching the overpass shall be 5 percent ( Figure 7.52.34 ).
• Geotechnical evaluations of existing soil conditions and recommendations for bridge abutments are required .
• When designing an overpass , the aesthetic appearance of the facility shall be considered so that it fits within the surrounding context .
Design Criteria :
• The overpass must meet bridge structural design standards and shall be designed to accommodate pedestrian , bicyclist , maintenance , and emergency vehicle loading .
• Bridges built over roadways , railroads , and waterways must maintain a minimum clearance under the structure . When designing a bridge structure , consult local , state , and federal design requirements for required clearance heights .
• Bridges built over waterways must not negatively impact the 100 year flood elevations . Consult engineering guidelines for clearance requirements when crossing over 100 year flood zone .
• Enclose overpasses with fencing and / or with safety railings to protect users .
• Railing fences or barriers on both sides of the path on a structure shall be a minimum of 42 inches high .
• On new bridge or overpass structures , the minimum clear width should be the same as the approach paved surface , plus a minimum of 2-foot-wide clear areas on each side . The clear areas provide the opportunity to avoid conflicts among bicyclists and railings , handrails , and other bicyclists who may have stopped on the bridge .
Figure 7.52.33 . Examples of multi-use trail overpasses .
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