Imagine a scene from the near-future: You get dropped off downtown by a driverless car. You slam the door and head into your office or appointment. But then where does the autonomous vehicle go?
It’s a question that cities would be wise to consider now. Self-driving cars may be on the roads within the next decade or two.
Automakers and specialized startups alike are developing automated vehicles, also known as AVs. Ride-hailing companies such as Lyft and Uber plan to operate some AVs. And other companies could start offering private robotaxis that drop owners off wherever they like and pick them up later.
Without policies to encourage sharing, it’s possible the roads could end up being crowded with private AVs. In a recent study of Seattle, we and our fellow researchers found that one of the biggest effects of AV technology may be on parking, as AVs leave expensive downtown spots behind in favor of cheaper parking outside the city center.
Parking uses a lot of land – and brings in big bucks
Researchers at UCLA have estimated that about 5% to 8% of urban land is devoted to curb parking. They’ve estimated that the parking coverage – the ratio of parking area to total land area – in downtown Los Angeles is about 81% and that in Houston 57%.
A 2018 parking study done by the Mortgage Bankers Association found that Seattle’s parking density of 29 parking stalls for each acre of land is twice its population density of 13 people for each acre.
Because driverless cars could park outside urban centers to avoid higher parking charges downtown, they could have a big effect on urban land use.
And there are possibly big monetary consequences. Many cities gather a substantial amount of money from parking-related activities. The 25 largest U.S. cities, collectively, got $1.5 billion in total revenue from parking fees and taxes in 2016.
In Seattle, for instance, the annual revenue from parking meters comes to about $37 million.
Lower demand for parking could mean this money– often used for schools, cultural resources and libraries – will need to be replaced.
Simulating a city with driverless cars
To gauge the likely effects of private AVs on parking, we used Seattle as a case study since data on all its off-street parking lots are available. We looked at energy use, emissions, parking revenue and vehicle miles traveled, among other things.
Our team obtained data from the Puget Sound Region Council on the daily occupancy and parking prices of all paid off-street parking garages and lots in downtown Seattle. We went on to identify places that are outside the downtown area and have many unrestricted parking spaces where vehicles can now park free of charge during the day.
Our simulation suggested that there is enough free parking just outside downtown Seattle that AVs would no longer choose to park in downtown lots. At current prices, it’s more economical to travel for free parking than to park in a paid lot.
Some private AV owners may rent out their car during the day as a ride-hailing service. For others, though, it might make financial sense to send their car home during the day and have it pick them up later. That would further increase vehicle miles traveled.
No more parking downtown?
As AVs leave downtown, parking revenues could decline to the point where owning a parking lot or garage would no longer be a good way to make money. This would present cities with both difficulties and opportunities.
We see a few ways that cities could respond.
For starters, cities could make use of congestion pricing. This is a fee or tax that users would have to pay before entering an urban center. Cities also could encourage more public transportation, as well as biking and walking. Or they could change the rules for parking in areas where it’s now unrestricted and free, or try a combination of these options.
Cities could further experiment with what’s called a scaled VMT tax: a fee that the operater of an AV would have to pay to enter a downtown zone and that would vary according to the number of miles the vehicle has traveled that day. This option might discourage an increase in housing sprawl and reduce the number of people using AVs to get downtown. In addition, encouraging AVs to be powered by electricity rather than gasoline would reduce the environmental consequences of any additional travel.
Much of the land now set aside for parking lots could be turned into parks, housing or commercial spaces. Having less curb parking could allow for wider bike lanes or sidewalks. To take advantage of changing parking demand, cities could build adaptable parking garages that could be used for other purposes. Garages with flat floors and exterior ramps, rather than interior ramps, could be fairly easy to use for commercial purposes or housing.
Cities would need to look for other sources of revenue to supplement the money lost from parking taxes, revenues and tickets. Some of this may be recovered through VMT and congestion fees, or by replacing underused parking structures with new denser uses.
Although robotaxis are not here yet, preparing now for changes in downtown parking and infrastructure could help cities respond when privately owned AVs start to hit the streets.
Corey Harper, Carnegie Mellon University and Constantine Samaras, Carnegie Mellon University