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J-1 APPENDIX J PRIMER ON DESIGNING BICYCLE FACILITIES When considering, planning, or constructing a bike facility, the first step is to identify the project scope. As more detailed information becomes available on site limitations, construction cost, and funding project impacts, the scope will be refined through the design develop- ment process. Basic considerations in defining the scope are facility type (on-street, off-street, equipment), paving, drainage, structures, and design guidelines used to identify dimensions such as width of paths. The following text provides some basics in identifying the project scope. When developing the cost of on-street bicycle facilities and shared use paths, the user will need to know how to select construction materials, recommend dimensions, and decide on a path surface. The following is a primer for design consideration of bicycle facilities. Pavement design focuses primarily on shared use paths and other off-street facilities. Bicycle facilities on roadways are considered to be a minor part of the structural design of the roadway and are there- fore not included as part of the primer. This primer should be used in conjunction with the 1999 AASHTO Guide for the Development of Bicycle Facilities. On-Street Facility On-street facilities consist primarily of paved shoulders, wide curb lanes, and bike lanes. All are part of the roadway surface that is also used by motor vehicles. Structural requirements of the road bed including pavement depth are dictated by motor vehicles: Paved Shoulders Critical dimensions ⢠Less than 4 feet (1.2 m): any additional width of paved shoulder is preferred than no facility at all, but below 4 feet a shoulder should not be designated or marked as a bicycle facility ⢠4 feet (1.2 m): minimum width to accommodate bicycle travel measurement must be of useable width and should NOT include the gutter pan or any area treated with rumble strips ⢠5 feet (1.5 m) or more: minimum width recommended from the face of a guardrail, curb or other barrier Widths should be increased with higher bicycle use, motor vehi- cle speeds above 50 mi/hr, and higher percentage of truck and bus traffic. Wide Outside Lanes Critical dimensions ⢠14 feet (4.2 m): recommended width for wide outside lane width must be useable and measurement should be from the edge line or joint of the gutter pan to the lane line ⢠15 feet (4.5 m): preferred where extra space required for maneu- vering (e.g., on steep grades) or to keep clear of on-street parking or other obstacles Continuous stretches of lane 15 feet (4.5 m) or wider may encour- age the undesirable operation of two motor vehicles in one lane. Where this much width is available, it is recommended to more seriously consider striping bike lanes or shoulders. Bicycle Lanes Critical dimensions Bicycle lane width ⢠4 feet (1.2 m): minimum width of bike lane on roadways with no curb and gutter ⢠5 feet (1.5 m): minimum width of bike lane when adjacent to parking, from the face of the curb or guardrail ⢠11 feet (3.3 m): shared bike lane and parking area, no curb face ⢠12 feet (3.6 m): shared bike lane and parking area with a curb face Bicycle lane stripe width ⢠6-inch (150 mm): solid white line separating bike lane from motor vehicle lane (maybe raised to 8-inches (200 mm) for emphasis) ⢠4-inch (100 mm): optional solid white line separating the bike lane from parking spaces Off-Street Facility (typically shared use paths) Standards recommend the width be 10 feet or 3 meters for a two-way, shared use path on a separate right of way. Other critical measurements include the following: ⢠8 feet (2.4 m) may be used where bicycle traffic is expected to be low at all times, pedestrian use is only occasional, sightlines are good, passing opportunities are provided, and maintenance vehicles will not destroy the edge of the trail ⢠12 feet is recommended where substantial use by bicycles, joggers, skaters, and pedestrians is expected, and where grades are steep ⢠2 feet of graded area should be maintained adjacent to both sides of the path ⢠3 feet of clear distance should be maintained between the edge of the trail and trees, poles, walls, fences, guardrails or other lateral obstructions ⢠8 feet of vertical clearance to obstructions should be maintained; rising to 10 feet in tunnels and where maintenance and emergency vehicles must operate
Drainage The AASHTO Guide recommends a cross slope of 2%. The fol- lowing are considerations to ensure adequate drainage: ⢠Slope the trail in one direction rather than having a crown in the middle of the trail ⢠Provide a smooth surface to prevent ponding and ice formation ⢠Place a ditch on the upside of a trail constructed on the side of a hill ⢠Place drainage grates, utility covers, etc., out of the travel path of bicyclists J-2 ⢠Preserve natural ground cover adjacent to the trail to inhibit erosion ⢠Include price of seeding, mulching, and sodding of slopes, swales, and other erodible areas in the cost Proper drainage is one of the most important factors affecting pave- ment performance. Proper drainage entails efficient removal of excess water from the trail. Surface water runoff should be handled using swales, ditches, and sheet flow. Catch basins, drain inlets, culverts and underground piping may also be necessary. These structures should be located off the pavement structure.
