How do current autonomous cars choose their speed?

June 30, 2018 3:58 PM

There are a few companies testing autonomous cars right now - how do the cars know how fast to go? Do they accept input from the "driver"?

I'm really hoping that autonomous cars will cut down on people speeding dangerously on residential roads. So my main purpose for asking is I hope the cars don't let their drivers tell them to do 40 in a 25. But I'm also just interested what the current state of the technology is.

posted by Tehhund to Technology (9 answers total)

I do not know the actual answer as almost everything about these cars is still trade secrets.

But most commercial basemaps know the speed limit for most US roads - I say most but I'm pretty sure they know the speed limit for every street in urban centers. There may be remote roads they don't know about. They are unlikely to be able to purposefully violate traffic laws.

In one of the few public pieces of data released we know that the Uber self-driving car involved in the pedestrian collision "was going about 40 miles an hour on a street with a 45-mile-an-hour speed limit".
posted by GuyZero at 4:09 PM on June 30, 2018 [3 favorites]

Fully autonomous cars will not let consumers control their speed in any meaningful way; part of the purpose of autonomous cars is to take bad human judgement out of the driving. As to what speed the cars will go, different groups are taking different approaches. Judging by limited public info, the Google team seems to put stock in cautious low speed for safety (as least until the state of the art is better), while the Tesla team seems to put stock in human-driver-like action improving safety by being better understood and predictable for surrounding drivers, which probably involves matching traffic flow to some extent (which might under some conditions put the car above the posted limit, though I think insurance/legal systems will have the final say on that). But really both groups (and others) will be doing both approaches, and a whole lot more.

TL;DR: The mothership will decide if/when the cars can exceed the posted limit.
posted by anonymisc at 5:02 PM on June 30, 2018 [3 favorites]

One of the keys to SDC's is the incredible GIS digital maps. I expect speed limit data is a combination of standard laws (35 unless otherwise posted in town X, for example), scraping city and state web sites, some optical recognition of speed limit signs by the mapping cars that have been driving around for years, and good old fashioned interns manually checking exceptions.
posted by sammyo at 6:34 PM on June 30, 2018 [2 favorites]

Fully autonomous cars will not let consumers control their speed in any meaningful way

Certainly it would be hard to imagine a getaway car mode but I can see having an interface where a passenger could request "please drive as slow as possible past the gardens" (or xmas lights, or monument)
posted by sammyo at 6:38 PM on June 30, 2018 [2 favorites]

Another possibility, folks for all the sad reasons are already using uber for emergency trip to a hospital so I can imagine, especially when most cars are autonomous, an emergency mode where a priority request is broadcast and the route is cleared ahead for a given car. With a significant fine for misuse.
posted by sammyo at 6:43 PM on June 30, 2018 [1 favorite]

Cadillac's super cruise system uses a five centimetre level map of speed limits. But it only works on limited access freeways.

I'm kind of interested in how it handles variable speed limits.
posted by Mitheral at 7:42 PM on June 30, 2018 [2 favorites]

Best answer: The cheap Garmin GPS in my car displays the current speed limit on the screen for every highway, road, and street that I drive on. It is so accurate that I can watch the displayed speed limit in the GPS change within 20 feet of passing a new speed limit sign. The GIS data maps seem to be quite accurate.

The display will also flash red if I exceed the current speed limit. So speed limits appear to be a solved technological issue for self-driving cars. Construction zones, traffic revisions and variable speed limits currently are not handled, but I can imagine in the near future these data being uploaded in near real time by road crews.
posted by JackFlash at 7:45 PM on June 30, 2018 [3 favorites]

A friend just bought a newer GPS system and its map appeared to know the location of the individual speed limit signs. For some reason it was set to flash an alert declaring that there was an upcoming sign every time we approached one, in addition to constantly displaying the current speed limit anyway.
posted by XMLicious at 5:25 AM on July 1, 2018 [1 favorite]

Construction zones, traffic revisions and variable speed limits currently are not handled

The app Waze handles most of that with a combo of crowd sourcing and I suspect google gis magic.
posted by sammyo at 8:11 AM on July 1, 2018 [1 favorite]