This article relies largely or entirely on a single source. (March 2012)
Parallel parking is a method of parking a vehicle parallel to the road (hence the term 'Parallel Parking'), in line with other parked vehicles. Parallel parking usually requires initially driving slightly past the parking space, parallel to the parked vehicle in front of that space, keeping a safe distance, then followed by reversing into that space. Subsequent position adjustment may require the use of forward and reverse gears.
Parallel parking is considered to be one of the hardest skills for new drivers to learn and is a required part of most road tests. Parallel parking enables the driver to park a vehicle in a smaller space than would be true of forward parking. Driving forward into a parking space on the side of a road is typically not possible unless two successive parking spaces are empty. Reversing into the spot via the parallel parking technique allows one to take advantage of a single empty space not much longer than the car (in order to complete the parking within three wheel-turns the parking space would generally need to be about one and a half car-length long).
New drivers learn to use reference points to align themselves in relation to the car in front of the space, to determine the proper angle for backing, and to determine when to turn the steering wheel while backing. They may find it easier to briefly stop at each reference point and turn for the next step.
Two major types of parallel parking technique differ in whether they will use two or three positions of the steering wheel while backing. A skilled driver is theoretically able to parallel park by having their car move along two arcs, the first having its center on the parking side of the car and the second having its center on the other side. There will be a point in the transition between these curves where all the car's wheels will be parallel with each other. Less-confident drivers may choose to drive further while transitioning, making it a pronounced middle step of three. Such a step allows greater tolerances to avoid hitting anything, but forces the car to start further from the road's edge and requires more space to the rear.
In the early 21st century, car manufacturers are addressing this need by introducing automatic parking.
Roads that facilitate parallel parking have an extra lane or a large shoulder for parked cars. It is also employed whenever parking facilities are not available—usually in large metropolitan areas where there is a high density of vehicles and few (or restricted) accommodations such as multi-storey car parks.
Many traffic regulators restrict parallel parking during rush hour, freeing up an extra traffic lane. Historically, metered parallel parking had individual meters for each parking spot with spots clearly marked on the road. Some regulators have eliminated individual spots allowing shorter vehicles to use less space. Individual meters are then also replaced with a centralized parking ticket machine.
Beyond taking up a lane of traffic, on-street parking further reduces road capacity as remaining traffic slows to interact with cars moving in and out of parallel parking spaces, car doors opening and pedestrians.