A bus bulb, also called a bus boarder or bus border, is an arrangement by which a sidewalk

Sidewalk

A sidewalk, or pavement, footpath, footway, and sometimes platform, is a path along the side of a road. A sidewalk may accommodate moderate changes in grade and is normally separated from the vehicular section by a curb...

 is extended outwards for a bus stop

Bus stop

A bus stop is a designated place where buses stop for passengers to board or leave a bus. These are normally positioned on the highway and are distinct from off-highway facilities such as bus stations. The construction of bus stops tends to reflect the level of usage...

; typically the bus bulb replaces roadway that would otherwise be part of a parking

Parking

Parking is the act of stopping a vehicle and leaving it unoccupied for more than a brief time. Parking on one or both sides of a road is commonly permitted, though often with restrictions...

 lane. With bus bulbs or boarders, a bus

Bus

A bus is a road vehicle designed to carry passengers. Buses can have a capacity as high as 300 passengers. The most common type of bus is the single-decker bus, with larger loads carried by double-decker buses and articulated buses, and smaller loads carried by midibuses and minibuses; coaches are...

 can stay in its traffic lane to discharge and pick up passengers, instead of having to pull over to the curb.

The term bus bulb is prevalent in North American usage, whilst bus boarder or bus border is used elsewhere.

A bus bulb or boarder can be considered as a specific form of curb extension

Curb extension

A curb extension is a traffic calming measure, primarily used to extend the sidewalk, reducing the crossing distance and allowing pedestrians about to cross and approaching vehicle drivers to see each other when vehicles...

, although that term is more normally used to describe a sidewalk extension for the purposes of traffic calming

Traffic calming

Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming...

 or other traffic management purposes.

Benefits

Benefits include preventing buses from being delayed by having to pull back into traffic, reducing risk of accidents, reducing pedestrian exposure in crosswalks (if provided at the same location), reducing sidewalk congestion, providing space for bus patron amenities including bus shelters, and traffic calming

Traffic calming

Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming...

. The protrusion also facilitates easier full length alignment of a bus entrance with a raised kerb stop, especially to allow level boarding in the case of low-floor bus

Low-floor bus

A low-floor bus is a bus that has no steps between one or more entrances and part or all of the passenger cabin. Being low floor improves the accessibility of the bus for the public, particularly the elderly or infirm, or those with push chairs, and increasingly, those in wheelchairs.In the modern...

es.

Bus bulbs also retain more parking when compared to a bus stop located in a parking lane, as a bus stop so located requires run-in and run-out tapers. Together these tapers may take up as much space as the actual stop, requiring parking to be prohibited over a longer length of road than with a bulb, where cars can park immediately on either side of the bus stop itself.

Drawbacks

The main drawback is for cyclists. The narrowing of the road can create danger for cyclists if the design does not take their needs into account. Bus bulbs are not appropriate on streets that provide only one traffic lane in each direction since they delay other vehicles that must wait behind the bus. Where more than one lane exists in one direction, modelling has shown that there is no additional delay overall for following drivers, since the buses have shorter dwell times (there is less time spent pulling back into traffic) and since following vehicles may use the second lane for passing.

Use in other transportation modes

Bulbs such as these are not limited to only buses; the Toronto Streetcar System

Toronto streetcar system

The Toronto streetcar system comprises eleven streetcar routes in Toronto, Ontario, Canada, operated by the Toronto Transit Commission , and is the largest such system in the Americas in terms of ridership, number of cars, and track length. The network is concentrated primarily in downtown and in...

, which operates mostly on traditional streetcar tracks

Tramway track

Tramway track is used on tramways or light rail operations. Grooved rails are often used in order to make street running feasible...

 in mixed traffic with cars, and has frequent request stops similar to bus routes, is introducing bulbs at some high-traffic stops and transfer points that have been recently renovated, notably on Roncesvalles Avenue

Roncesvalles Avenue

Roncesvalles Avenue is a north-south arterial street in Toronto, Canada. It connects Queen Street West, King Street West and runs north to Dundas Street West. Roncesvalles Avenue takes its name from the Battle of Roncesvalles, which took place in the Roncesvalles gorge in Spain in 1813...

. There are three expected goals for these bulbs:

• Prevent vehicles from parking in front of streetcar stops.
• Increase standing room on the often restricted sidewalks at stop locations in some of the densest regions of the city.
• Improve safety for passengers boarding and alighting at these stops; unmodified stops require passengers to step into traffic to board/alight. The safety concerns are mostly with regard to drivers not from Toronto
  Toronto
  Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...
  
   who are inexperienced at driving among streetcars
  Tram
  A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...
  
  in mixed traffic.