As the term is used in this guide, a bus lane is a traffic lane on a surface street reserved for the exclusive use of buses. With curbside bus lanes, bicyclists and right turners are usually permitted. In a very few cases, carpools are also allowed. Reserved lanes help buses pass congested traffic. Giving buses this type of priority makes sense when they carry many more people than general traffic. However, bus lanes are subject to the same perception problem as expressway HOV lanes: even when a bus lane has a higher throughput (persons per hour) than other traffic lanes, it may appear under-used. A certain amount of illegal use can be tolerated, provided that the lane does not get clogged.

Curbside Lanes

Bus lanes can be located either at the curb or in the median. It is hard to keep curbside lanes uncongested. The major threats to smooth curbside bus lane operation are (1) illegal parking and standing and (2) right turning vehicles waiting for pedestrians. One solution to the first problem is to designate the next lane away from the curb as the bus lane (see photo), thereby providing a legal place for curbside parking (but double parking may still block the bus lane!). Some spots can be reserved for deliveries. One solution to the second problem is to prohibit right turns at locations where serious delays would otherwise be encountered. Another solution is also using the lane adjacent to the curb lane as a bus lane and mark a right-turn-only lane next to the curb at intersections with heavy right-turn volumes.

  [All-day bus lane.] This San Francisco bus lane is the lane adjacent to the curb lane and is in effect weekdays 7 am to 6 pm. Curbside deliveries and parking are still possible, except at stops.

Bus lanes are frequently in effect only during the peak hours in the peak direction. A curbside parking lane which becomes a travel lane during peak hours is a very similar type of traffic management device and may have similar effects on traffic. Because buses stop in the travel lane in such situations, there is no delay in reentering traffic (see discussion under Stop Spacing and Design).

[Peak period bus lane.] This bus lane, also in San Francisco, is located against the curb and is in effect during the evening peak only (4 pm to 6 pm).

On Madison Avenue in New York City, both the curb lane and the next lane over are designated as bus lanes. Right turns are prohibited. Taxis are permitted in the lanes. This design permits buses to pass eachother.

Median Lanes

[Buses using median busway in Curitiba, Brazil (Photo: Martha Welborne)] Bus lanes can also be located in the median, usually of a wide boulevard. Many similar reservations were created for trolleys, a few of which still exist. Some of these rights-of-way were converted to bus use, for example, Canal Street in New Orleans and Market Street in San Francisco (both of which now have shared trolley and bus use). Median lanes are usually separated from general traffic lanes by a raised curb. Passenger platforms are usually on the right, and can be staggered to reduce the overall width needed. Center platforms can also be used, but this requires left-side doors on all vehicles using the median lanes. If there is sufficient room, median lanes can be designed to permit buses to pass each other, but this is not always feasible.

Median lanes are much less likely to be congested by other traffic than curbside lanes. On the other hand, they do present a few disadvantages relative to curb side lanes:

Left-turning traffic conflicts with straight-through buses. Either left turns must be banned or they must be permitted only in a separate phase.
Passengers must cross traffic lanes to reach stops. Where there are several lanes of fast traffic, this can create safety problems, especially since passengers often are anxious to cross when they see a bus approaching.
Because of the need for passenger loading areas in the center of the street, the overall street width needed can be larger than in the case of curbside lanes.

Contraflow Lanes

Another option is to provide a contraflow lane, a bus lane in the opposite direction on what would otherwise be a one-way street. Contraflow lanes sometimes can provide more direct routing for buses when one-way street patterns create detours. Contraflow lanes do not have the same enforcement problems as curbside lanes, since violators are easy to spot and catch.

Most contraflow lanes in the past were installed adjacent to the curb. This design prevents the use of the curb for deliveries, which may be a serious problem for businesses without rear loading access, such as via side streets or alleys. One solution to this problem was devised in San Francisco in 1997. The next lane from the curb on Sansone Street was designated as a contraflow bus-only lane. The curb lane was reserved for commercial deliveries, and commercial vehicles were authorized to use the lane. Essentially the project involved the conversion of a northbound one-way street with three travel lanes and curb parking into a two-way street with a southbound lane and curb parking restricted to buses and commercial vehicles.

The Lymmo downtown circulator in Orlando, FL provides another option in bus lane design. For most of the route, the Lymmo travels on streets that were formerly three-lanes in the same direction (one-way streets). After conversion to bus lanes, the right-most lane remains for general traffic use and provides access to on-street parking. The center lane (see photo) was converted to a bus-only lane, with a raised curb separating it from the general traffic lane and providing space for loading.  [Orlando's downtown circulator bus operates on paired exclusive lanes.] The left-most lane becomes a bus-only lane for opposite-direction bus traffic; loading is on the opposite sidewalk and there is no on-street parking on that side. These configurations can produce complication at intersections. Orlando's solution was to provide separate bus phases, controlled by special bus-only signals, at every intersection, to permit buses to make all movements free of conflicting traffic moves. These signals are only activated when an approaching bus is detected.

The Bus Lane Paradox

Bus lanes can provide a strong identity for public transit. They can reduce travel time, but only if they are designed to work properly. A single curbside lane is rarely effective. Designs which are self-enforcing, which accommodate commercial deliveries, and which permit stopped buses to be passed by other buses can be most useful. However, such designs may occupy a significant amount of street space. Where traffic is severely congested, bus lanes can provide the biggest benefit to bus passengers, but it is precisely in these places where it may be difficult to reduce the amount of space available for general traffic— and thereby seem to worsen congestion. Conversely, where there is plenty of road space available, it may be easy to install bus lanes, but they will provide few benefits, given that traffic is not likely to be congested.

On some urban streets, bus passengers account for a surprisingly high percentage of total person throughput. Focusing on moving people instead of simply moving vehicles will help to justify priority treatments for buses. Where transit users are a small fraction of street users, it will be more difficult to justify such treatments.