Bus Stop Spacing

Bus stop spacing has a major impact on transit performance. Stop spacing affects both access time and line-haul time, and therefore affects the demand for transit service. In general, there is a tradeoff between: (a) closely spaced, frequent stops and shorter walking distance, but more time on the vehicle and (b) stops spaced further apart and longer walking distance, but less time on the vehicle.

Some of the findings of optimization studies are:

• As acceleration or deceleration rates increase, optimal stop spacing will narrow (i.e., an intermediate stop imposes a smaller time penalty).
• As steady running speed attained after acceleration increases, optimal spacing will widen (i.e., an intermediate stop will impose a greater time penalty).
• As the speed of the feeder mode is increased, optimal spacing will widen.
• As dwell time is reduced, optimal spacing will narrow.

Although analytical studies to determine optimal stop spacing provide some useful guidelines, stops must ultimately be sited to serve major trip generators and attractors in the service area. To the degree that a BRT is emulating a light rail system, a useful benchmark is the actual stop spacing of LRT systems in the U.S. (see table).

Over time there is a tendency for additional stops to be added to bus routes, as requests for service in front of more places are accepted. When stops are as frequent as every or every other city block, it may be useful to comprehensively re-examine the location of all stops. In addition to reducing the number of stops, citing stops so as to improve service (as discussed below) can be a component of a BRT project.

Limited-stop service is used frequently on high-demand bus corridors in combination with local service. BRT projects can also involve adding limited-stop service, perhaps overlayed over existing service.

Bus Stop Location

Whether a bus stop should be located at the near side of the intersection, the far side of the intersection, or at mid-block has been a source of debate. In general, far-side stops are preferable; however, other types of stops may be justified in certain situations (TCRP). There are advantages and disadvantages to each location (see table). Extensive discussion and guidance for determining proper bus stop location for a given site context are provided in both Giannopoulos and TCRP.

For BRT systems which include (a) bus detection and active signal priority or (b) queue jumper lanes, bus stops should be at the far side. This permits effective use of these priority measures to clear the bus through the intersection with minimal delay. Otherwise, the added bus dwell time variability from a near side stop would complicate, if not preclude, bus detection and green phase extension.

A near side stop would also prevent effective use of a queue jumper lane (with or without an advanced bus signal) since the adjacent queue of through traffic would already be discharging from the stop line by the time the bus was ready to depart from the near side stop. Instead of having a "jump" on the queue of traffic in the adjacent through lanes, the bus would have to merge with it. There would be very few gaps of adequate size because of the compressed queue of traffic discharging from the intersection at a saturation rate of flow. The bus would experience a delay equal to the time for the queue to clear the intersection, or the sum of this clearance time and the cross traffic green time if the bus is forced to wait to the next signal cycle.

Merging Delay

Buses often experience substantial delays when reentering the traffic stream after a curbside stop in the parking lane or in a bus bay, a paved area outside the travel lanes. This type of delay does not occur if the bus travels and stops in a curb lane (where on-street parking is not permitted). As far as bus passengers and operators are concerned, it is best to avoid the use of bus bays if possible. If a bus bay is deemed necessary, it should have tapered deceleration and acceleration lanes and be located at the far side of the intersection to take advantage of interruptions in the traffic stream from the upstream traffic signal.

One can calculate the bus merge delay upon reentering a traffic stream as a function of both the adjacent lane’s traffic flow and the critical gap length needed by the bus operator to merge. The point with significant delay is above 450 vehicles per hour per lane (vphl) (TCRP, p. D-43). For a four mile trip, the cumulative delay can be in excess of ten minutes.

Priority Merge Rule

One way of substantially reducing the delay to a bus reentering a traffic stream after a parking lane, curbside stop is to adopt a priority merge rule. This is a section of the vehicle code that requires all vehicles to yield the right of way, when safe to do so, to buses signalling to reenter the traffic stream a stop. This rule is common in Europe, Australia, and Japan. Washington State adopted priority merge in 1993, Oregon in 1997, and Florida and British Columbia in 1999. The rule is typically advertised on the rear of buses. Even though not every vehicle will yield with a priority merge rule in place, the chance that at least one vehicle will yield can significantly reduce merging delay. The Oregon version of the rule reads as follows:

"(1) The driver of a vehicle shall yield the right of way to a transit vehicle traveling in the same direction that has signalled and is reentering the traffic flow.
(2) Nothing in this section shall operate to relieve the driver of a transit vehicle from the duty to drive with due regard for the safety of all persons using the roadway."

The Florida version of this rule applies only to buses stopped at "a specifically designated pullout bay." In British Columbia, the rule applies only on roadways with a speed limit of 60 km/h (37 mph) or less and also specifies that a driver must only yield when it is safe to do so. The introduction of the rule in May 1999 was accompanied by a "Yield to Bus" public awareness campaign.

In addition to a reduction in bus merging delay at each stop, other significant benefits of a priority merge rule include: reduced waiting times for passengers at bus stops due to reduced irregularity of the service, decreased travel time for passengers, less stress on bus operators, and less impact on bus operations due to traffic congestion. A priority merge rule is consistent with providing a Bus Rapid Transit service.

Bus Bulbs

One option to eliminate merging delay is to restrict parking during peak periods. The curb lane remains the bus stopping lane and there is no re-entry delay. The curb lane can be designated as a bus lane during peak periods only. In either case the problem is preventing illegal parking or standing. Even a few vehicles violating the restrictions can defeat their purpose.

Bus bulbs are a section of sidewalk that extends from the curb of a parking lane to the edge of the through lane. When used as a bus stop, the buses stop in the traffic lane instead of moving into the parking lane.

 Adding a bus bulb permits installing a bus shelter even on a narrow sidewalk.

Advantages of a bus bulb include:

• Permits more on-street parking
• Decreases the walking distance (and time) for pedestrians crossing the street
• Provides better sight lines to bus patrons waiting for the bus
• Provides additional sidewalk area for bus patrons to wait
• Segregates waiting bus patrons from circulating pedestrian flow on the sidewalk
• Results in minimal delay to the bus and its on-board passengers by reducing bus merge delay
• Provides additional space for amenities including bus shelters

With a bus bulb, buses stop in the travel lane and therefore there is no delay in re-entering the traffic stream.

Some disadvantages of a bus bulb are:

• Can cause traffic to queue behind a stopped bus, thus causing traffic congestion
• May cause drivers to make unsafe maneuvers when changing lanes in order to avoid a stopped bus
• Costs more to install compared with curbside stops, particularly for addressing street drainage requirements

How much delay is there to people in vehicles queued behind a bus stopped at a bus bulb compared to the bus passenger delay avoided by not having to merge back into the traffic stream?

For an indication of the tradeoff between the delay imposed on persons in a queue of vehicles behind a stopped bus versus the person- seconds of delay avoided by avoiding a bus merge maneuver, consider the following example. Assume an average passenger vehicle occupancy of 1.1, and a discharge headway of 2.5 seconds per vehicle. For a traffic flow of 700 vphl, and a critical gap size of 10 seconds, the bus merge delay is 24.2 seconds. Assuming a net departure bus occupancy of 30 persons after loading at the bus bulb during a dwell time of 20 seconds, the person-seconds of delay avoided equals (24.2) * (30) = 726 seconds or 12.1 minutes. The delay to the queued vehicles is 42.7 person-seconds The net gain or reduction in person delay is therefore (-726)+(42.7) = -683.3 seconds or 11.4 minutes saved.

Bus Shelter Design

Bus shelters—or stations—can be used to differentiate and brand BRT service and to provide passenger information and amenities. The shelter design should have a common and consistent look across the BRT system, but with allowance for differences to permit stations to harmonize with the local urban fabric, perhaps referencing the history of the area. The stations on the Dallas LRT Transitway are an excellent model combining simplicity, functionality, integration with the urban fabric, and good design.

There are several manufacturers who specialize in specialized, modular shelters. Whether adapting a manufactured shelter or using a custom design, some general factors to consider include:

• The use of vandal-resistant and graffiti-resistant materials.
• The use of environmental design to assure a defensible space by providing good curb-side and street-side surveillance, day and night.
• Siting of the shelter to prevent interference with pedestrian circulation.
• Efficient layout of interior spaces, with consideration to inclusion of off-vehicle fare collection technology such as contactless smart card readers linked to a gate control system.
• Designs that permit efficient, orderly and rapid flow of alighting and boarding passengers from the stop to the vehicle.
• Access to the shelter by persons using mobility aids, with a good spatial connection to the ramp or lift on the bus.

REFERENCES

Giannopoulos, G., Bus Planning and Operation in Urban Areas: A Practical Guide, 1989.

TCRP. Transit Cooperative Research Program. Report 19, Guidelines for the Location and Design of Bus Stops. Transportation Research Board. National Academy Press. Washington, DC, 1996.