Driverless cars will transform car park design

The adoption of autonomous vehicles could significantly reduce the amount of urban land dedicated to parking, a study by Canadian academics suggests

Driverless cars will have a major impact on parking facility designs in the future. In the future autonomous vehicles (AVs) will drop off their passengers, navigate to a dedicated AV parking lot and return later to pick up the passenger. Research by the University of Toronto’s Department of Civil Engineering shows how that adoption of self-driving cars could significantly reduce the amount of urban space dedicated to parking. While traditional car parks are configured for islands of cars that can each pull in or out of a spot, the researchers suggest an AV parking lot could resemble a solid grid, with outer cars moving aside as needed to let the inner cars enter and exit. Cars in the outer rows of the grid can move out of the way to allow cars in the middle to escape and then return to their bays.

“In a parking lot full of AVs, you don’t need to open the doors, so they can park with very little space in between,” says Professor Matthew Roorda (CivE), senior author of the journal Transportation Research Part B. “You also don’t need to leave space for each car to drive out, because you can signal the surrounding AVs to move out of the way.”

The researchers’ challenge was to determine the optimal size of the grid to maximize storage while minimizing the number of moves required to extract any given car. “There’s a trade-off,” says Mehdi Nourinejad, a PhD graduate from the Department of Civil Engineering and the study’s lead author. “If you have a very large grid, it leads to a lot of relocations, which means that it takes longer on average to retrieve your vehicle. On the other hand, if you have a number of smaller grids, it wastes a lot of space.”

Compared with regular car parks that have only two rows of vehicles in each island, future car parks for autonomous vehicles could have multiple rows of vehicles stacked behind each other. Although this multi-row layout reduces the space required, it can cause blockage if a certain vehicle is barricaded by other vehicles and cannot leave the facility. To release barricaded vehicles, the car park operator has to relocate some of the vehicles to create a clear pathway for the blocked vehicle to exit. The extent of vehicle relocation will depend on the layout design of the car park. 

Nourinejad, Roorda and their co-author Sina Bahrami (CivE PhD candidate) created a computer model in which they could simulate the effects of various layouts for AV parking lots. They then used an algorithm to optimise the design for various factors, including minimising the number of relocations and maximising the proportion of the lot that was used for parking versus lanes for relocation, entering or exiting.

The team’s analysis showed that, for a given number of cars, a well-designed AV parking lot could accommodate 62% more cars than a conventional one. Depending on the car park’s dimensions, they were able to increase the capacity even further: a square-shaped AV parking lot could accommodate up to 87% more cars. 

This improved use of space could translate into much smaller parking lot footprints, provided the total number of cars that need to park in them remains constant. Another advantage of AV car parks is that the design is not fixed. “For example, if you need to pack more cars into the lot, you don’t need to paint new parking spaces. Instead, the operator can just signal the cars to rearrange themselves. It will take longer to retrieve your vehicle, but you will fit more cars in,” says Bahrami.

The revitalisation of space that was previously used for parking can be socially beneficial if car parks are converted into commercial and residential land-uses.

Professor Roorda hopes that municipal parking authorities will be able to use their design approach to enhance urban spaces. “Right now, our downtown cores have giant municipal parking lots next to major attractions,” he says. “AVs could allow us to both shrink and relocate these parking lots, opening up valuable space in cities.”

However, the academics recognise that there could be negative consequences, such as a potential increase in traffic congestion. “Right now, we have a lot of cars on the road with just one passenger,” says Roorda. “If we locate AV parking lots too far away from major attractions, we could end up with streets crowded with vehicles that have zero passengers, which would be worse.”

Another drawback is that the team’s designs only work for parking lots reserved exclusively for AVs, rather than a mix of AVs and conventional vehicles, though Roorda says that a single car park could have both AV and non-AV areas. Roorda and his team also cannot predict when the number of AVs on the road will reach the critical mass required to make use of their designs. “We’re talking about large numbers of vehicles that can fully drive themselves, with no requirement for a driver to take over if something goes wrong,” he says. “There’s a lot that has to happen before we get to that stage.”

The research is part of the iCity: Urban Informatics for Sustainable Metropolitan Growth project, an initiative of the University of Toronto Transportation Research Institute. It is funded by the Ontario Research Fund, Research Excellence and a consortium of industrial partners.

The team's research, Designing parking facilities for autonomous vehicles, is published in the journal Transportation Research Part B: Methodological. The research is part of the iCity: Urban Informatics for Sustainable Metropolitan Growth project, an initiative of the University of Toronto Transportation Research Institute. It is funded by the Ontario Research Fund — Research Excellence as well as a consortium of industrial partners.