Car park layout: bay sizes, aisles and circulation

The car park bay size and aisle width most authorities start from is 2.4 m by 4.8 m with a 6.0 m aisle for 90-degree parking, and a growing number now ask for 2.5 m by 5.0 m. Neither figure is in a statute. They come from local highway authority parking standards, usually published as a supplementary planning document or an appendix to the local plan, and they vary. So the first task on any layout is to find the authority's own standard and design to it, because a layout drawn to a remembered dimension will be rejected by a highway officer with a scale rule.

What is in national guidance is the accessible bay geometry and the charging provision, and those are the two elements that most often force a layout to be redrawn.

Standard bay dimensions and where they come from

The 2.4 m by 4.8 m bay dates from an era of smaller cars and persists because the arithmetic is convenient: three bays to a 7.2 m structural grid. Vehicles have grown. A current large family car is close to 4.9 m long and nearly 2.0 m wide across the mirrors, which is why authorities have drifted towards 2.5 m by 5.0 m and why users of a 2.4 m bay open their doors into the next car.

Design to the larger dimension where the site allows it, even if the standard permits the smaller one. A car park that works is worth more than two extra bays that nobody can use.

Those are field conventions drawn from typical authority standards, offered for illustration. The authority's published figures govern.

Aisle widths for one way and two way flow

Aisle width and bay angle are a single decision, not two. Ninety-degree bays need the widest aisle because a car has to turn through a right angle to enter, and they give the most bays per unit area and two-way circulation. Angled bays need a narrower aisle, park more easily, and force one-way circulation with a loss of efficiency.

Six metres is the conventional two-way aisle for perpendicular parking. Narrow it and the manoeuvre needs a three-point turn, which is where a swept path analysis will show the vehicle crossing into the opposing bay. Widen it beyond 6.5 m and drivers treat it as a road.

Two details catch people out. A dead-end aisle needs a turning head, because the last bay cannot be reached and left without one, and a hammerhead costs a bay or two at the end of every run. And a one-way system needs enforcement by geometry rather than by signs: build in a pinch point or an angled bay set, because painted arrows alone are ignored.

End bays, columns and wall clearances

A bay with an obstruction along one side is not a usable bay at the nominal width. Add at least 300 mm where a bay abuts a wall, a fence, a column or a planter, and more where the obstruction runs the full length of the bay rather than sitting at one end.

In a multi-storey or undercroft structure the column grid drives everything. The standard arrangement puts three bays between column lines, giving a 7.2 m or 7.5 m grid, with columns set at the rear of the bays rather than between them. Across the structure, two bay depths plus an aisle gives 4.8 plus 6.0 plus 4.8, or 15.6 m between column lines, and 16.0 m if the bays are 5.0 m deep.

Get that grid agreed with the structural engineer before the layout is drawn. A column landing 600 mm into a bay is a bay lost, and on a 200 space deck a misaligned grid can cost a dozen spaces.

The last bay in a run against a wall at the end of an aisle is the one that will be left empty for the life of the building. Either enlarge it properly or use the space for something else, such as the powered two-wheeler parking the layout also needs.

Accessible bays and their transfer zones

This is where national guidance applies. Approved Document M sets the geometry for a designated parking bay: a 2.4 m by 4.8 m bay with a 1.2 m wide access zone alongside and a 1.2 m zone to the rear, giving an effective 3.6 m by 6.0 m where the side zone is not shared between two bays.

Three points that layouts get wrong.

1. The side access zone can be shared between a pair of bays, which saves width, but a shared zone has to be properly marked and kept clear, and it cannot be used as a pedestrian route.
2. The rear zone is for loading a wheelchair from the boot and must not be the circulation aisle. A bay drawn at 4.8 m with the aisle immediately behind it does not comply.
3. Headroom on the route to accessible bays and at the bays themselves needs to accommodate high-roofed adapted vehicles, which means more than the general car park figure. Take 2.6 m as the working number and confirm against the current Approved Document.

On numbers, the guidance approach for non-domestic buildings is one space for each disabled employee plus a percentage of total capacity for visitors, commonly taken as 5 per cent. For residential schemes in London the London Plan requires a proportion of spaces to be accessible from the outset with provision to convert more later. Distance matters as much as number: designated bays should be as close as possible to the accessible entrance, with 50 m generally treated as the outer limit.

The detail of numbers, dimensions and distances is set out more fully in the note on accessible parking dimensions, numbers and distances.

Charging bays and the equipment they need

Approved Document S governs charging infrastructure for new buildings. In outline, a new dwelling with an associated parking space gets a charge point, and a new non-residential building with more than ten spaces needs at least one charge point plus cable routes for a proportion of the remaining spaces. Check the current Approved Document for the exact figures, because the requirement has been amended since it came into force in 2022.

The layout consequence is physical space that designers forget to allocate.

A wall-mounted unit needs a clear zone in front of it and a position that does not obstruct the access zone of an adjacent accessible bay. A bollard-mounted unit needs a footprint, protection from vehicle impact, and a cable management arrangement that does not trail across a pedestrian route. Tethered cables need somewhere to live. And the distribution equipment, from a substation to a distribution board and metering, needs a plant position with ventilation and access, which is not a parking space.

Accessible charging is the element most often missed entirely. A charging bay that is also a designated accessible bay needs the charging equipment positioned so it can be reached from a seated position and so the cable does not cross the transfer zone, and there is a published specification covering accessible charging that the design should be checked against.

Build the charging strategy into the layout at the first iteration. Retrofitting a charge point run along the back of a bay row usually means losing bays to a cable route.

Pedestrian routes through the car park

Every car park has pedestrians in it, and most layouts treat them as an afterthought. Officers increasingly do not.

Provide a defined route from the furthest bay to the building entrance, segregated from the vehicle route where the car park is large enough to justify it, at least 1.2 m wide and preferably wider, with dropped kerbs and tactile paving at crossings, and lighting to a specified level. Do not run the pedestrian route behind a row of bays, because that is the reversing zone.

Where the car park serves a school, a nursery or any use with a pronounced arrival peak, the pedestrian design matters more than the bay count, and the issues set out on school access, drop-off and school streets apply directly.

Drawing the layout so it can be checked

An officer needs to be able to verify your layout with a scale rule in ten minutes, and the drawing either lets them or does not.

Draw at 1:200 for anything up to a few hundred spaces, and dimension the bay width, bay length, aisle width, accessible bay zones and the structural grid on the drawing rather than in a note. Hatch and label each bay type, and provide a bay schedule giving standard, accessible, charging, family and operational spaces with a total that matches the policy requirement. Show swept paths for the design vehicle at every constrained movement, including the dead-end aisle and the entrance from the highway. Show the pedestrian route as a continuous line. Show levels and gradients, because a sloping bay is a problem and an accessible bay has to be effectively level.

Submit that with a transport statement for a smaller scheme, or inside the transport assessment for a larger one, and include the authority's standard alongside your provision in a two-column table. Where the provision falls below the standard, evidence the case with a parking survey rather than an assertion about car ownership.

This is general guidance, not legal advice; check the position with your local planning authority and against the current Approved Documents before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. You can enter the site postcode to see which transport reports a scheme is likely to need.