Design and Engineering

• On-Street Facilities
• Sidewalks
• Shared Use Paths
• Intersections
• Barriers
• Traffic Calming
• Signage and Pavement Markings
• Universal Design/ADA
• Construction Access

The design guidelines in this chapter are intended to serve as a primer on bicycle facilities for planners, engineers and others in accommodating bicycle traffic in different riding environments. Appropriate facility design also encourages predictable bicycling behavior. The guidelines are based on the national guidelines as outlined in AASHTO’s 1999 Guide to the Development of Bicycle Facilities and the USDOT’s Manual of Uniform Traffic Control Devices, but also considers other information (see References).

These guidelines should be used in conjunction with, not separate from, the AASHTO and MUTCD documents. The information here highlights important issues, but more detail is contained in the national documents. Bicycle facility guidelines will not cover all the details encountered in the development of facilities. Where details are not covered, appropriate engineering principles and professional judgement must be applied in providing for the safety and convenience of bicyclists, pedestrians and motorists. The human and environmental factors contributing to bicycle crashes are important for facility designers to be aware of. Bicycle facilities, which include bike lanes, wide curb lanes and designated shoulders, should be included as part of all appropriate projects unless there is a compelling reason not to include them (see US DOT Policy Statement). Judging the need for facilities based on current bicycle counts or projected levels is often unreliable due to existing disincentives for bicycling. Paved shoulders, bike lanes and wide curb lanes provide a number of other benefits related to maintenance, general safety and joint uses, and can often be justified for these reasons.

Since facilities are constructed on a project-by-project basis, bicycle facilities should generally be provided even for short sections (like intersection improvements or bridges). If desired and appropriate, bike facility signing and marking can be delayed until the segment is connected to a longer facility. If the justification for bicycle facilities is questioned (e.g. due to the need to purchase additional right-of-way or remove parking), the priority level of the project should be examined.

On-Street Facilities

The appropriate bicycle facility for any given roadway depends on the roadway’s classification, pavement and right-of-way width, motor vehicle speeds, traffic volumes, adjacent land use and other factors. On-street facilities typically consist of bicycle lanes, paved shoulders, wide curb lanes and shared roadways. The travel volumes and choice of roadway design will affect the level of use by bicyclists. For example, a four-lane divided highway with high traffic speeds and volumes, even with paved shoulders, will attract only more experienced bicyclists. Bicycle facilities are needed on major roadways despite the limited use by bicyclists in order to provide access to destinations and to get across barriers (e.g. interstates or rivers). No one type of facility will serve all bicyclists.

Streets on which traffic is traveling at higher speeds than they were designed for can be made more suitable for bicyclists through traffic calming. In rural areas, the suitability of a roadway decreases as traffic volumes reach 1,000 ADT because of higher traffic speeds and a larger percentage of truck traffic.

Signed Shared Roadway
Using signage to identify preferred bike routes can be used in certain situations:

• The route provides continuity to other bicycle facilities such as bike lanes and shared use paths.
• The road is a common route for bicyclists through a high demand corridor.
• In rural areas, the route is preferred for bicycling due to low traffic volume or paved shoulder availability.
• The route extends along local streets and collectors that lead to an internal neighborhood destination such as a park, school or commercial district.

Signing of shared roadways indicates that there are advantages to using these routes compared with other routes. This means the responsible agencies have taken action to ensure that these roadways are suitable for bicycling and will be maintained.

Bike Lanes
Bike lanes are provided on arterial and major collector streets. Bike lanes may also be used on rural roadways near urban areas, where there is high potential for bicycle use. Bike lanes are generally not recommended on rural highways with posted speed limits of 55 mph because of difficulties at intersections. Shoulder bikeways should be used in these situations.

Bike lanes are one-way facilities that carry bicycle traffic in the same direction as adjacent motor vehicle traffic. Bike lanes should always be provided on both sides of a two-way street. Motorists are prohibited from using bike lanes for driving and parking, but may use them for emergency breakdowns or avoidance maneuvers.

Bike lanes are designated with pavement markings as well as signs along the street. A typical bike lane width is 5’ from the face of curb or guardrail to the bike lane stripe. Bicycle lane widths of 6 feet maximum may be desirable when one or a combination of the following conditions exists:

• traffic volumes and speeds are high;
• adjacent parking use and turnover is high;
• catch basin grates, gutter joints and other obstacles are present in the bicycle lane
• steep grades exist;
• truck volumes are high;
• bicycle volumes are high.

Bicycle lane widths of 4’ minimum may be acceptable when:

• physical constraints exist (for a segment of less than 1 mile that links to existing bikeways on both ends);
• implemented in conjunction with traffic calming devices;
• adjacent to parking with very low use and turnover, and low speed limits and traffic volumes;
• adjacent to an uncurbed street shoulder.

Additionally, for on-street parking, an 8’ (7’ minimum) parking area width adjacent to the bicycle lane is recommended.

The travel lane width adjacent to a bicycle lane should be 11’ (10’ minimum). A 4’ bicycle lane should not be used in combination with a 7’ parking lane and/or a 10’ travel lane.

Since bicyclists tend to ride a distance of 32 – 40” from the curb face, it is vital that this surface be smooth and free of structures. Drainage grates and utility covers that extend into this zone may cause cyclists to swerve and effectively reduce the width of the bike lane. Where these structures exist, it may be necessary to increase the bike lane width accordingly.

Among the benefits of bike lanes are:

• Defining a space for bicyclists to ride, helping less experienced cyclists feel more confident and willing to ride on busier streets;
• Reducing motorist lane changing when passing bicyclists;
• Increasing the visibility of bicyclists in the transportation system.

Other benefits include:

• Reducing pedestrian/bicyclist conflicts due to fewer cyclists on the sidewalks;
• Creating a buffer between pedestrians and motor vehicles;
• Increasing effective turn radii at driveways and intersections;
• Improving sight distances;
• Providing space for emergencies/breakdowns.

Bicycle lanes can be implemented by narrowing existing travel lanes; removing a travel lane; removing parking, except where it is essential to serve adjacent land uses; and shoulder widening. Bicycle lanes may be implemented through stand-alone bikeway projects, through reconstruction or construction of roadways, and through routine resurfacing of roadways when the street configuration can be modified without parking removal or serious additional congestion.

Some streets where bicycle lanes are the preferred treatment have circumstances that make bicycle lane installation very difficult. These circumstances include: harm to the natural environment or character of the natural environment due to additional pavement; severe topographical constraints; economic or aesthetic necessity of retaining parking on one or both sides of the street; and serious traffic congestion that would result from eliminating travel lanes. These circumstances are to be evaluated very carefully before a decision is made to implement an alternative treatment.

For example, before deciding that on-street parking is necessary, off-street (including driveways and garages) and alternative parking opportunities (such as parking on the opposite side of the street) must be investigated. As another example, a travel lane should be removed even if traffic congestion may increase, unless the congestion that may be caused by lane removal cripples the flow of people and goods.

Traffic calming improvements, wide outside lanes or alternative parallel bikeways may be substituted only after careful investigation has proven bicycle lanes to be unfeasible.

Among the benefits of bike lanes are:

• Defining a space for bicyclists to ride, helping less experienced cyclists feel more confident and willing to ride on busier streets;
• Reducing motorist lane changing when passing bicyclists;
• Increasing the visibility of bicyclists in the transportation system.

www.pedbikeimages.org/Dan Burden

Other benefits include:

• Reducing pedestrian/bicyclist conflicts due to fewer cyclists on the sidewalks;
• Creating a buffer between pedestrians and motor vehicles;
• Increasing effective turn radii at driveways and intersections;
• Improving sight distances;
• Providing space for emergencies/breakdowns.

Bicycle lanes can be implemented by narrowing existing travel lanes; removing a travel lane; removing parking, except where it is essential to serve adjacent land uses; and shoulder widening. Bicycle lanes may be implemented through stand-alone bikeway projects, through reconstruction or construction of roadways, and through routine resurfacing of roadways when the street configuration can be modified without parking removal or serious additional congestion.

Some streets where bicycle lanes are the preferred treatment have circumstances that make bicycle lane installation very difficult. These circumstances include: harm to the natural environment or character of the natural environment due to additional pavement; severe topographical constraints; economic or aesthetic necessity of retaining parking on one or both sides of the street; and serious traffic congestion that would result from eliminating travel lanes. These circumstances are to be evaluated very carefully before a decision is made to implement an alternative treatment.

For example, before deciding that on-street parking is necessary, off-street (including driveways and garages) and alternative parking opportunities (such as parking on the opposite side of the street) must be investigated. As another example, a travel lane should be removed even if traffic congestion may increase, unless the congestion that may be caused by lane removal cripples the flow of people and goods.

Traffic calming improvements, wide outside lanes or alternative parallel bikeways may be substituted only after careful investigation has proven bicycle lanes to be unfeasible.

Wide Curb Lane
For streets with traffic volumes of more than 3,000 ADT and speeds above 30 mph where there is inadequate width to provide the required bicycle lanes or shoulder bikeways, a wide curb lane (or wide outside lane) may be provided that accommodates both cyclists and motor vehicles. This could occur on retrofit projects where there are severe physical constraints, and all other options have been pursued, such as removing parking or narrowing travel lanes to minimum acceptable widths.

A wide curb lane is typically 14’ wide. Usable width is normally measured from curb face to the center of the lane stripe, but adjustments need to be made for drainage grates, parking, and longitudinal ridges between pavement and gutter sections. For widths of 15’ or more, a bicycle lane or shoulder bikeway should be striped.

Shoulder Bikeway
Adding or improving paved shoulders is often the best way to accommodate bicyclists on rural roads. Paved shoulders have many benefits for motor vehicle traffic, as well as for cyclists. Shoulders should be at least 4’ wide for bicycle travel. However, where 4’ is not feasible, any shoulder width is preferable to none. It is desirable to increase the shoulder width where higher levels of bicycling are anticipated. Additional width is also needed when motor vehicle speeds exceed 50 mph or when the percentage of truck traffic is high.

Rumble strips or raised pavement markers are not recommended where shoulders are used by bicyclists unless there is a minimum clear width of 1’ from the rumble strip to the traveled way, 4’ from the rumble strip to the outside edge of the paved shoulder or 5’ to the adjacent guardrail or curb.

On projects that widen shoulders for the benefit of bicyclists, there may be some opportunities to reduce costs by building to a lesser thickness. If the following conditions are met, 3” to 4” of asphalt and 2” to 3” of aggregate over existing roadway shoulders may be adequate:

• There are no planned widening projects for the road section in the foreseeable future.
• The existing shoulder area and roadbed are stable and there is adequate drainage or adequate drainage can be provided without major excavation and grading work.
• The existing travel lanes have adequate width and are in stable condition.
• The horizontal curvature is not excessive, so that the wheels of large vehicles do not track onto the shoulder area. On roads that have generally good horizontal alignment, it may be feasible to build only the inside of curves to full depth.
• The existing and projected average daily traffic and heavy truck traffic is not considered excessive (e.g., under 10% of total).

The thickness of pavement and base material will depend upon local conditions and engineering judgment should be used. If there are short sections where the travel lanes must be reconstructed or widened, these areas should be constructed to normal full-depth base design standards.

On-Street Parking
On-street parking increases the potential for conflicts between motor vehicles and bicyclists. Bicyclists are susceptible to opening car doors, vehicles exiting parking spaces and obscured views of intersecting traffic. For shared use between bicyclists and parking, a minimum width of 12 feet is recommended. A 5’ bike lane and a 7’ parking lane should be striped in order to define the parking spaces and give bicyclists adequate room to avoid hazards.

Innovative Treatments
Treatments such as raised bike lanes, bicycle boulevards and colored bike lanes have been used in other communities. The purpose of these treatments is to improve safety for bicyclists by either increasing the separation from motorized traffic or raising the motorists’ awareness of bicyclists. The success of these treatments has not yet been fully determined.

Policies:

• Fully integrate the use of a consistent set of bicycle facility design standards, based on the 1999 AASHTO Guide for the Development of Bicycle Facilities and the bicycle facility guidelines included above.
• On arterial and collector roadways, provide on-street bicycle facilities with a Bicycle Compatibility Index (BCI) of “C” or above.
• Seek to provide a higher BCI on roadways included in the bicycle system.

Action Steps:

• Provide for appropriate access control on arterial roadways in order to increase the function and safety of these roadways for both bicyclists and motorists, while at the same time ensuring adequate access and crossing opportunities for pedestrians and bicyclists.
• Continue to research innovative treatments used in other communities and determine if they would be applicable in Knoxville.

Sidewalks
In general, the designated use of sidewalks for bicycle travel is not recommended. Widening sidewalks does not necessarily enhance the safety of sidewalk bicycle travel, because the extra width encourages faster bicycle speeds which increases the potential for conflict with motor vehicles at intersections and with pedestrians along the corridor.

Sidewalk bikeways should only be considered under limited circumstances:

• To provide bikeway continuity along high speed or heavily traveled roadways having inadequate space for bicyclists, and uninterrupted by driveways and intersections for long distances.
• On long, narrow bridges. In such cases, ramps should be installed at the sidewalk approaches. If approach bikeways are two-way, sidewalk facilities also should be two-way.

In residential areas, sidewalk riding by young children is common. This type of sidewalk bicycle use is accepted, but it is inappropriate to sign these facilities as bike routes.

Policy:

• Evaluate the need for sidewalk bike facilities on a case-by-case basis using the criteria stated above.

Shared Use Paths
Shared use paths, or trails, are facilities on exclusive right-of-way and with minimal cross flow by motor vehicles. Users are non-motorized and may include in-line skaters, bicyclists, pedestrians, joggers and wheelchair users. These facilities are usually designed for two-way travel and can serve a variety of purposes, from recreation to transportation. These paths should be considered as a part of an overall bicycle system, not as a substitute for on-street bicycle facilities. In some communities, greenway systems include shared use paths. Depending on the funding source and purpose, all greenway trails may not be designed to AASHTO guidelines. Shared use paths within greenway systems that could receive high levels of bicycle use, however, should follow AASHTO.

The key components to successful shared use paths are:

• Continuous separation from traffic (e.g. along a river or railroad);
• Scenic qualities;
• Connection to major destinations (e.g. shopping malls, downtown, schools, parks);
• Well-designed street crossings;
• Shorter trip lengths than the road network offers;
• Visibility (e.g. proximity to housing and businesses);
• Good design; and
• Proper maintenance.

Shared use paths along roadways may be appropriate if the following conditions are met:

Bicycle and pedestrian use is anticipated to be high;

The adjacent roadway has high traffic volumes and speeds with no room for on-street bike facilities;

The path will generally be separated from motor vehicle traffic with few driveway or roadway crossings; and

There are no reasonable alternatives for bikeways on nearby parallel streets.

Policies:

• Avoid locating shared use paths adjacent to roadways unless above guidelines are met.
• Design new shared use paths according to AASHTO standards.

Intersections

Most conflicts between motorists and bicyclists occur at intersections. Good intersection design indicates to road users what path to follow and who has the right of way. Bicyclists’ movements are complicated by their lesser speed and visibility.

Traffic signals should allow enough time for bicyclists to cross the intersection. Signal timing along a corridor can be a problem for cyclists who are trying to maintain a constant speed to take advantage of their momentum. The cyclist may be able to get through a few lights, but then has to stop and wait, and then have to build up momentum again. This can tempt bicyclists to run red lights out of frustration. Traffic signals in downtown and other dense areas should be timed for speeds of 12–16 mph, which would allow bicyclists to ride with traffic.

Demand-actuated signals, which usually use loop detectors embedded in the pavement, are often problematic for bicyclists. There are several improvements that can be made to help cyclists:

• Place loop detectors in bike lanes, especially on side streets with lower traffic volumes.
• Increase sensitivity of detectors.
• Paint stencils to indicate the most sensitive area of the loop.
• Place push-buttons close to the roadway for cyclists to reach without dismounting.
• Use quadrupole loop detectors rather than the standard square loops.
• Use visual or motion detection rather than loop detectors.

Policies:

• Use quadrupole loop detectors at all signalized intersections.
• Consider visual or motion detection at locations where a high level of bicycle use exists or is anticipated.
• Consider the needs of bicyclists when designing and reconstructing intersections.
• Consider bicyclists when coordinating traffic signal timing along a corridor.

Barriers

Barriers to bicycle travel include rivers, major roadways, and railroads. Barriers, or “weak links” in the bicycle system, can seriously inhibit bicycling in a community by making it difficult to travel safely to destinations. A good implementation plan should address these issues.

Circles
In general, cyclists often complain that they feel “squeezed” by motor vehicles trying to pass at a traffic circle. On streets where bicycle lanes are recommended (generally on streets above 5000 ADT), speed humps are preferable to traffic circles. When implementing traffic circles, careful consideration should be given to the impact of the circle on bicycle travel.

Curb Extensions
On streets without a centerline stripe, motor vehicles can safely pass cyclists at an intersection with a curb extension. On streets with a centerline stripe, the curb extension should be placed such that a 12’ (minimum) to 14’ (preferred) outside lane is left on the roadway to allow bicyclists to pass through the intersection safely. A 10’ auto lane next to a 4’ (minimum) bicycle lane is also acceptable. Otherwise, bicyclists will have to veer out into traffic, or motor vehicles will “squeeze” bicyclists going through the intersection.

www.pedbikeimages.org/Dan Burden

www.pedbikeimages.org/Dan Burden

Diverters
All traffic diverters should preserve bicycle turning movement options and through access unless overriding safety concerns exist. A bicycle “cut-through” at full diverters should be wide enough (4’) to accommodate a bicycle trailer.

Narrow Lanes
Narrowing lanes by adding striped bike lanes or a striped shoulder can be used to reduce traffic speeds, and improve the street for bicyclists.

Policy:

• Traffic calming programs shall consider the needs of bicyclists in design and engineering.

Action Step:

• Develop a funded Traffic Calming Program in each jurisdiction.

Signage and Pavement Markings

Well-designed roads usually require very little signing, because they are built so all users understand how to proceed. An overabundance of warning and regulatory signs may indicate a failure to address design problems. The attention of drivers, bicyclists and pedestrians should be on the road and other users, not on signs along the side of the road.

Part 9 of the Manual on Uniform Traffic Control Devices 2000 and the 1999 AASHTO Guide to the Development of Bicycle Facilities should be followed in providing traffic controls for bicycle facilities. See also signage policies.

Universal Design/ADA

The American Disabilities Act was signed into law in 1990. The US Access Board is responsible for developing accessibility guidelines to ensure that new construction and reconstruction covered by ADA is readily accessible and usable by people with disabilities.

Universal design, also called accessibility, refers to facility designs that accommodate the widest range of users. Anything that makes facilities more accessible for people with disabilities improves accessibility for everyone. For example, curb ramps are necessary for wheelchair users but also aid parents with strollers or carts, child cyclists, rollerbladers and the elderly.

Construction Access

Access for bicyclists must be maintained during construction and other projects disrupting travel, particularly on bridges. Bicyclists are sensitive to changes in their normal travel routes because of their slower speeds and exposure to noise, dirt and fumes. Temporary lane restrictions, detours and other traffic control measures instituted during construction should be designed to accommodate non-motorized travelers whenever possible, especially in areas where bicycling is common.

If the disruption occurs in a bicycle lane over a short distance (approximately 500’ or less), bicyclists should be routed to share a motor vehicle lane. For longer distances or on busy roadways, a temporary bicycle lane or wide outside lane should be provided. Bicyclists should not be routed onto sidewalks with pedestrians unless the traffic engineer deems there to be no reasonable alternative. If the proposed work is on a designated bikeway and there can be no accommodation for bicyclists, a reasonable detour needs to be established and signed (refer to the Manual on Uniform Traffic Control Devices, Part 9).

Important considerations for street disruptions include:

• Metal plates create a slick and dangerous surface for cyclists, and are not easily visible at night or in the rain. If metal plates are to be used to accommodate traffic, the plates may not have a vertical edge greater than one inch without a temporary asphalt lip to accommodate bicyclists. Barricades with flashers should be placed at least 20 feet in advance.
• Construction holes or depressions should never be left without physical barriers preventing cyclists from falling in. For holes that need to be left for over two days, temporary fill should be used to create a level surface for the hole or depression. If the hole is to remain for less than two days, barricades with flashers should be placed to prevent cyclists from riding into it.
• In all cases of road surface construction or other disruptions, barricades with flashers should be placed at least 20 feet in advance.
• The placement of advance construction signs should not obstruct the bicyclist’s path. Where there is sufficient room, placing signs half on the sidewalk and half on the roadway may be the best solution where there is no planting strip.

Action Steps:

• Develop a policy requiring that bicycle and pedestrian access be maintained during construction. When access is not feasible, detour routes should be as short as possible.
• Educate project managers about the policy and its significance.
• Provide better signage during construction to indicate work in progress, road or path conditions and, alternate route information when applicable.