A Challenge to Right-Angled Parking Bays

When a leading UK mathematician suggested that diagonal bays may be both more efficient and easier to use, he sparked a lively debate within the industry. The University of Salford’s Professor David Percy believed that the problem with traditional right-angled parking spaces is that the lanes need to be wider so that drivers can swing round enough to get into the bays. Instead, he proposed that 45 degree diagonal parking bays require less course adjustment, so the access lane can be narrower, leading to an efficiency saving of 23% as more parking bays can be incorporated into the same space.

Little did he realise that his theoretical, geometry and trigonometry based assumptions would be widely picked up by the press and that his claims would lead to a raft of requests for car parking design to take account of his calculations.

At Hill Cannon Consulting, whilst we were reluctant to directly contradict an academic professional, faced with the rising tide of similar design requests we felt we needed to set the record straight.

Hill Cannon’s Steve Vollar said; “Following The Times article we have had clients wanting us to adopt angled parking, so have had to demonstrate that it is less efficient in practice. For busy surface car parks the reduced lane width is not safe for pedestrians’ wheelchairs and pushchairs, thus wider lanes are needed and are even less space efficient.

“The determining factor with an elevated car park is the support structure such that column positions are important and with the construction economics a modular approach is needed, unless the client has a large budget, which is sadly an infrequent event. We have published a designer’s guide based on our consultancy experience, but are always seeking means to develop and improve our designs.

“In fact, angled parking is not a new method and has been around for decades and featured in all issues of the Institution of Structural Engineers’ Car Park Designers’ Hand-book. The system is popular in non-city centre US car parks where cars are typically larger and drivers are less inclined to tight manoeuvres and land is not at a premium.

“The most popular are 70 degree angled bays, more efficient than 45 degrees. Angled parking can reduce the bin width but extends lane lengths and at the edges the remnant triangles add non-useable space. By reference to the Car Park Designers Handbook conventional 90 degree parking has a space efficiency of 18.72m/space whilst 45 degree angled parking has a space efficiency of 20.5m/space for internal bays and 21.96m/space for external bays.

“Where space permits, angled bays offer easier manoeuvreability but not mor efficiency. For structured multi-storeys add in the supports and the cost over 90 degrees parking bays is significant and thus not a common sight. Thus, the benefits of angled parking will not be endorsed by the commercial developer.

“It is encouraging to have an academic input into parking design and we are happy to engage in dialogue. We have a number of designs where the design was determined by site constraints as sites are often too small for an ultra-efficient layout.”

Hill Cannon’s Glynn Rhodes added that a wealth of literature and research that has been published on car park design over the past four decades. “As parking consultants who have been involved in the design of parking layouts for the past 40-plus years we have always been aware that whilst angled parking makes it easier to park a car the use of angled parking has hardly ever been adopted in the design of new car parks because of the inefficient use of the available space. This knowledge has existed and been the subject of various publications dating back to the 1970s.

“A typical comparison was undertaken as shown in the drawing opposite. This shows that although the overall width of the car park is reduced the gross floor area per space increases by 20.9m/ per space for 90 degree parking amd 6m wide aisles to 26.6m per space for a 45 degree parking and 3.6m wide aisles.

“Therefore angled parking in this case is 27% less efficient and contradicts Professor Percy’s assertion that; ‘For a large car park, a 45 degree bay angle can lead to an efficiency saving of 23%. An exercise we did compared well with Jim Hill’s example of ‘bin geometry’ featured in the 1990 BBC publication Multi-Storey Car Parks.”

Rhodes added that as well as efficiency there are other issues to consider with angled parking. “Angled parking does not always fit well with standard modular forms of construction for multi-storey car parks.” He says, “With 90 degree parking and 6m wide aisles there is space in the 6m wide aisle for a 3.6m wide traffic aisle and two 1.2m wide pedestrian routes either side of the central aisle. With a 3.6m wide aisle used for 45 degrees parking where do the pedestrians go, and what about people in wheel chairs and parents with children in buggies?

“Angled parking with 3.6m wide aisles may be user friedndly for drivers but not so for pedestrians once they have left their car. With angle parking and 3.6m wide aisles the turning distance between the aisles at the end of the parking bays is reduced and will involve a ‘full-lock’ turn for larger cars; not a user-friendly feature.

Fortunately, we were pleased to hear that Professor Percy had taken Hill Cannon’s experts’ opinions in good spirit. He responded to our team saying; “Thank you for your informative message. I realise that angled parking is not new and I should clarify that I have little knowledge of car park design. My report that caught the media’s attention was merely an interesting exercise in geometry and trigonometry for a mathematics magazine.

“I believe that car park optimisation software exists in the USA and a mathematician from Bristol University published a detailed report on the subject in 2013. You might be pleased to hear that he advises against angled parking which agrees with your conclusion.

“In particular my calculations were based on generous dimensions and a large, single-storey car park, so might be of little practical benefit. As such my claimed 23% efficiency for bays at 45 degrees might not be realisable in real situations.

“Indeed, I since investigated a local car park and found that the best option has bays at 50 degrees with an apparent 9% improvement in efficiency compared with a rectangular grid. Given the extra complexity of painting and the associated possibility of error, I recommended that the rectangular grid be maintained.

“As you rightly indicate, the introduction ofirregular boundaries and supporting columns in multi-storey car parks further reduces any potential benefits of angled bays.

“In short, I now plan to leave real car park design to the experts and wish you well in your endeavours!”