AVs cruising will slow us all down, modelling suggests

Most concerns about driverless cars focus on what they might hit while they’re moving, but Adam Millard-Ball suggests we also give some thought to what happens if they keep on moving.

Autonomous vehicles (AVs), as they are otherwise known, have no need to find a parking spot, let alone pay for one, so there’s nothing to stop them just cruising around until needed. 

To make matters worse, because cruising is less costly at lower speeds, they’ll slow to a crawl. They not only won’t mind a bit of congestion, they’ll be quite happy to create it.

If that sounds like the makings of a traffic nightmare, Millard-Ball, an associate professor of environmental studies at the University of California, Santa Cruz in the US, can confirm your fears.

Using game theory, a traffic microsimulation model and data for San Francisco, he predicts that as few as 2000 AVs would slow downtown traffic to less that 3.5 kilometres (two miles) an hour. And that’s the best-case scenario. 

“It just takes a minority to gum things up,” he says. “Drivers would go as slowly as possibly so they wouldn’t have to drive around again.” 

Millard-Ball says his study is the first to analyse the combined impact of AVs and parking costs on city centres, where the cost and availability of parking is the only tool that effectively restricts car travel. And that’s perhaps surprising, considering quite a bit of research is being done into how to adapt to the inevitable arrival of AVs – including where to park them all.{%recommended 7487%}

Free cell-phone parking areas, coupled with strict enforcement in loading areas, relieve snarls at airport snarls, Millard-Ball says, but cities will be hard-pressed to provide remote parking areas for AVs at rates lower than the cost of cruising.

“Even when you factor in electricity, depreciation, wear and tear, and maintenance, cruising costs about 50 cents an hour: that’s cheaper than parking even in a small town,” he says. “Unless it’s free or cheaper than cruising, why would anyone use a remote lot?”

Regulation would also be tricky. “It’s difficult to regulate intent. You can pass a law saying it’s illegal to drive more than 10 minutes without a passenger, but what if the car is picking up a parcel?”

The answer, Millard-Ball suggests in a paper published in the journal Transport Policy, is a greater focus on congestion pricing – but with a twist.

“Because the ability of AVs to cruise blurs the boundary between parking and travel, congestion pricing programs should include two complementary prices – a time-based charge for occupying the public right-of-way, whether parked or in motion, and a distance- or energy-based charge that internalises other externalities from driving,” he writes.

And the time to do it is now, he suggests, before there are enough people with vested interests and an axe to grind. 

“As a policy, congestion pricing is difficult to implement. The public never wants to pay for something they’ve historically gotten for free,” he says. 

“But no one owns an autonomous vehicle now, so there’s no constituency organised to oppose charging for the use of public streets. This is the time to establish the principle and use it to avoid the nightmarish scenario of total gridlock.”

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