Recommended Design Standards

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This chapter presents guidelines for designing, striping, signing or otherwise designating bicycle facilities, intersections, or roadways to improve bicycle safety.

The design criteria of the California Highway Design Manual (HDM), and the California Traffic Manual are hereby incorporated by reference. This chapter presents guidelines for how to apply Caltrans' minimum design criteria for bike paths and bike lanes.

In addition, this chapter recommends design treatments for particularly difficult situations for bikes (such as at right-turn lanes and off-ramp right-turn merges with city streets). It also presents recommended signs or pavement legends that, although not contained in the Traffic Manual, will be essential for the complete and effective implementation of the bikeway network. Most of these installations (or variations) are being used in other cities in the U.S.

Bike Paths

The City has relied on the bike path design standards of the HDM, which call for a minimum 8-foot paved path and recommend 12 feet where pedestrians are expected. The default design practice in San Francisco in many cases is 8 feet, regardless of the expected or actual pedestrian use. Figures 5-1 through 5-5 present guidelines for paths of various design specifications. (All figures are presented at the end of this chapter.) These are intended as guidelines rather than hard and fast design standards. But, if followed they will increase the utility of the facility to all potential users.

Where short bike paths are recommended to connect two segments of a route, an 8-foot paved width is probably adequate. Of course, if such a bike path segment will essentially double as a sidewalk and have many pedestrians, 8 feet may not be adequate. Engineering judgement will need to be exercised on a case by case basis. Such short segments are generally less than 500 feet or so in length (see Figure 5-1).

An 8-foot cross section is also adequate for a bike path of any length where few or no pedestrians are expected. However, given the density of San Francisco, this situation is probably rare. Most bike paths will be essentially multi-use trails, and thus should be designed to more than minimum standards. The more pedestrians or non-bicycle users projected, the wider the path should be. For paths with low pedestrian volumes, (approximately 50-100 per peak hour) minimum paved width is recommended to be 10 feet and the minimum recommended cross section is depicted in Figure 5-2. For moderate pedestrian volumes (approximately 100-400 per peak hour), the recommended cross section is depicted in Figure 5-3 with a paved width of between 12 and 16 feet. For heavy pedestrian volumes (greater than approximately 400 per peak hour), two parallel facilities are recommended: one for faster traffic, such as bicycles and roller blades, and one for slower modes such as pedestrians, children on training wheels, etc. This is depicted in Figure 5-4.

Finally, in areas where automobiles can be prohibited, a road restricted to bicycle use would be an excellent way to provide mobility to bicycles and to safely separate the slower users. Such a facility would have the look and feel of a traditional road and could in fact serve as emergency vehicle or maintenance vehicle access if needed. Examples of appropriate locations for a bikes-only road could be in the Presidio and in redevelopment areas, especially if reducing dependence on the automobile is to be encouraged.

One of the most dangerous conflict points along a two-way bike path is its intersection with cross streets. To increase motorists' awareness that bike traffic is crossing in both directions, an 8-foot band of distinctive colored pavement, as illustrated in Figure 5-6, should be considered for the bicycle's path across the intersection. This design is currently used in the City of Montreal, and the design specifications for the colored pavement surface are presented in Appendix D.

Bike Lanes

While the minimum bike lane width specified in the HDM is 4 feet (5 feet with parking), this minimum design standard should be reserved for situations that are not worst-case in terms of traffic volume and speed. On streets with over 500 vehicles per hour per lane (vphpl) and/or speeds of 35 mph or more, the goal should be bike lanes of 6 to 8 feet in width. The recommended bike lane width and travel lane widths for a given curb-to-curb width are presented in Table 5-1. Special consideration should be given to travel lane widths on streets with high volumes of heavy trucks and MUNI routes.

On steep grades where pavement widening potential is limited and extra width or a bike lane can only be provided on one side of the road, the bike lane or extra width should be provided in the uphill direction as downhill bicyclists are more capable of keeping up with the flow of traffic.

Class III Bike Routes and Wide Curb Lanes

By their very nature, wide curb lanes and Class III bike routes require no special markings. However, it is recommended that a pavement stencil, as illustrated as Item 10 in Figure 5-7, be used in the right-hand portion of the lane. This stencil should be supplemented with "Share the Road" signs (Item 2) for lane widths of 12 to 14 feet and with "Bikes Allowed Use of Full Lane" (Item 4) for lane widths of under 12 feet. These signs are illustrated in Figure 5-7. The City may also wish to use these signs and stencils on roads which are not designated bikeways as bicyclists have the same rights on every road. It is not the intent that such signs be posted on every road. It is recommended that, in addition to designated bikeways, these signs and pavement stencils be used on roadways with heavy traffic volumes and narrow lanes i.e. more than 600 vphpl and curb lane widths of 14 feet or less (22 feet or less with parking).

The pavement stencil should be painted every 200 feet and placed so that the center of the stencil is eleven feet from the face of curb when parking is allowed. Appendix D contains the design specifications used by the City of Denver, developer of this stencil. City staff and the bicycle community will work together to obtain approval from the California Traffic Control Devices Committee (CTCDC) for these signs and pavement stencils.

Recommendations at Right-Turning Situations

Right-Turn-Only Lanes - Many accidents are caused by a motor vehicle's improper turn or not yielding the right-of-way to the bicyclist. A common conflict point is at intersections when a motorist wants to turn right across the path of a bicyclist proceeding straight. This is a problem with and without dedicated right-turn only lanes. Right-turn-only lanes present two difficulties to bicyclists:

In order to improve safety at right-turn only lanes, the right-turning motorists need to be made aware of the presence of bicyclists, and bicyclists need to be made aware of the correct position to ride through the intersection. The following is recommended:

Right-Turn Merge - Many right-turn lane junctions with City arterials have been designed to facilitate a high speed merge. Examples are freeway off-ramps merging with City streets (e.g. US 101 at Cesar Chavez Street) and free right-turn lanes from one arterial to another (e.g. the Oak Street merge between Stanyan and Shrader Streets). These high speeds are usually inappropriate for travel along the arterial, and expose bicyclists to unnecessary serious risk of injury. Recommended signing and striping plans are presented in Figures 5-9 and 5-10 for three situations:

i. An off-ramp merge with an arterial;

ii. An off-ramp with added lane junction with arterial - no bike lane; and

iii. An off-ramp with added lane junction with arterial - with bike lane.

In addition, Item 9 in Figure 5-7 presents a sign to be used in the situation of an on-ramp diverging from an arterial, for example eastbound Cesar Chavez Street at southbound Bayshore Boulevard on-ramp or the southbound 101 on-ramp.

Transit Island - Bicyclists currently experience difficulty passing buses stopped to the right of transit islands. The minimum curb-to-curb width for such installations should be 14 feet, as illustrated in Figure 5-11.

Miscellaneous Signs

Figure 5-7 presents signs that are recommended for use in San Francisco even though they are not contained in the Traffic Manual. Some of these signs may have to receive approval from the California Traffic Control Devices Committee (CTCDC). Item 3 presents a sign currently used in Santa Cruz County to warn all modes that traffic laws are strictly enforced. This sign is recommended in locations where compliance with traffic control devices has been exceptionally low. Items 6, 7 and 8 are recommended signs to be used in conjunction with Traffic Calming strategies; all are currently used by the City of Palo Alto. Item 8, "Cross Traffic Does Not Stop" is generally recommended only when a four-way STOP has been converted to a two-way STOP.

Development/Redevelopment Areas

New developments and redevelopment projects offer an opportunity to make a truly bicycle friendly roadway network. Roadways within such areas should at a minimum conform to the design standards discussed above. All arterials should be designed with bike lanes, and preferably, on-street parking should be prohibited. The minimum bike lane width should be six feet. For example, Third Street through Mission Bay should have 6-foot-wide (minimum) bike lanes.

Residential streets should be designed with design speeds of less than 25 mph using traffic calming design features described in Chapter 6. Urban design features should be incorporated which minimize the attractiveness of the automobile and support bicycling and walking. Collector streets should be designed with a speed limit of 25 mph. If projected traffic volumes are more than 4,000 vpd, then bike lanes should be provided. All new developments in the City should be connected to the recommended bicycle network.

Bike paths should be provided along places of scenic beauty, particularly along the waterfront and ocean. The Presidio has numerous possibilities to have bike-only roads. These would be compatible with the National Park character of the Presidio, as bike and pedestrian modes are the most environmentally benign.

Intersection Control

For bicyclists, travel is generally easy once momentum has been gained. STOP signs require the bicyclist to come to a complete stop, and thus lose his/her momentum which they must then work to regain. On the recommended routes and roads that have a high degree of bicycle travel, STOP signs should be removed where they do not meet warrants, and cross traffic should be required to stop. For a more thorough discussion of traffic calming techniques, see Chapter 6.

Signal Timing

Signal timing has been used with great success for motorists in San Francisco to improve traffic flow and reduce delay. The same reasons that make it desirable for motoristsCconstant and efficient speedsCmake it desirable for bicyclists. Where possible, the City should consider timing the signals along bike routes for bicycle speedsCapproximately 12 to 15 miles per hour.

Minimum green times at actuated signals should take bicyclists into account. Bicyclists need more start-up time than motor vehicles. Actuated signals should be timed so that the minimum green time is at least 8 seconds where grades are flat. On routes with an upgrade, bicyclists need even more time. At intersections along major thoroughfares, particularly with widths of 75 feet or more, red clearance intervals should be provided to allow time for bicyclists to clear the intersection before cross-traffic is given a green indication. A recent research paper for the California Bicycle Advisory Committee provides additional discussion on the issue of signal timing for bicycles.

Vertical Step Height

When paved street surfaces are interspersed by manholes, drainage grates, the seam between asphalt roadways and the concrete gutter, or other obstacles, it is important that they be set flush with the paved roadway. According to Highway Design Manual Standards, when the step between the pavement and obstruction is greater than 3/4 of an inch perpendicular to travel, and 3/8 inch parallel to travel, it poses a threat to safe riding conditions for bicyclists. Ideally, whether perpendicular or parallel to travel, the allowable tolerance in roadway surface should be within 1/4 of an inch.

Miscellaneous Obstructions and Hazards

Manholes, drainage grates, and construction road plates also pose problems because of their slippery surfaces and/or grooves which can cause bicycles to slip or get caught, and thus fall over. Although they pose a greater danger to the beginner bicyclist, even the most advanced cyclist faces a risk when riding at night or in heavy traffic volumes which leave no choice but to ride over the obstacle. When possible, road construction plates and manhole covers should be treated with a non-skid surface, or ordered as such. The City of Toronto, Canada has experience with such treatments.

Drainage grates and railroad tracks present the possible danger of catching a wheel and throwing a bicyclist from their bicycle at worst, or causing expensive wheel damage at best. A discussion of methods for mitigating these risks is given in Chapter 8 under maintenance policies.

Speed bumps damage bicycles' wheels just as they are intended to damage cars at high speeds. Fortunately, City policy has been not to install them. Speed humps, which have a more gradual incline, are acceptable if designed correctly. A more thorough discussion of speed humps is provided in Chapter 6. Rumble strips are another common problem for bicyclists. As per the Traffic Manual, they should only be installed where other measures have proved ineffective. When raised ceramic markers are installed as rumble strips, they should not be installed clear to the edge of the travelled way. A clear space of 18 to 24 inches through which bikes may travel should be provided at the right-hand edge and in the center of the travel lane.

 

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. ⁽⁾ Signal Clearance Timing for Bicyclists, Alan Wachtel, John Forester, Gary Foxen and David Pelz.