# How do self-driving cars deal with stoplights? **URL:** \ **Category:** Factual Questions\ **Created:** [April 3, 2016, 5:08am UTC](https://boards.straightdope.com/t/how-do-self-driving-cars-deal-with-stoplights/751031 "2016-04-03T05:08:05Z")\ **Posts on this page:** 4\ **Page:** 7
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 14, 2016, 1:31am UTC](https://boards.straightdope.com/t/how-do-self-driving-cars-deal-with-stoplights/751031/121 "2016-04-14T01:31:32Z")
> [@Chronos](#): > > I’m not so sure. My mom and I are both urban, and as a result, if one of us wants to visit the other, it’s a ten-minute drive. That’s not much of a chore: Honestly, it’s probably more work to get the dog kenneled and the house locked up and gather up whatever the reason for the visit is. But in some rural areas, a “neighbor” might be an hour or more away. And it’s a lot more useful to free up an hour of the car-user’s time than it is to free up ten minutes. The benefit for rural drivers is certainly there as you say. It was the many folks in many threads talking about trying to get a self-driving car to understand their unmapped dirt roads, deep snow, roads with no lines, finding the right parking space in a farm yard, etc., that make me think they’re gonna be underserved until late in the AI car switchover. And that these folks are gonna demand pickup trucks for their legit needs; short-range Googlepods won’t do it for them. Not that those issues are necessarily show-stoppers for rural-appropriate AI vehicles. But they will be a long way from the fat part of the market that Google, Apple, Tesla, _et al_, will be targeting at first. Sorry I wasn’t a bit more specific in what I meant. ---
**Author:** ![JRDelirious](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jrdelirious/32/9531_2.png) [@JRDelirious](https://boards.straightdope.com/u/JRDelirious)\ **Post date:** [April 14, 2016, 3:01am UTC](https://boards.straightdope.com/t/how-do-self-driving-cars-deal-with-stoplights/751031/122 "2016-04-14T03:01:22Z")
> [@LSLGuy](#): > > A corollary to this is that early self-driving cars need to be really, really good. Not just so-so. Which may prove to be the biggest obstacle to getting from here to there. Right. If the human driver has to be watching out all the time in case she needs to take over, then she might as well be driving and in that case why buy the automaton car, which at introduction will be more expensive than the conventional one. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 14, 2016, 3:13am UTC](https://boards.straightdope.com/t/how-do-self-driving-cars-deal-with-stoplights/751031/123 "2016-04-14T03:13:29Z")
> [@usedtobe](#): > > Am I the only one to see the (rather large) problem with Default=On with brakes? > > Zipping down the road at 70 mph is NOT the time for a hiccup causing “Invoke Default”. > > Unless every other pod for the 10 miles behind also slam on the brakes simultaneously. > > Not a good idea. except that’s more or less how the air brakes on heavy trucks work. the air pressure from the engine-driven compressor _disengages_ the brakes. when the driver presses the pedal, the actuators at the wheels release the air pressure and the springs let the (self-energizing) drum brakes engage. and in the event of a loss of air pressure, the brakes will fully engage. ---
**Author:** ![drachillix](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@drachillix](https://boards.straightdope.com/u/drachillix)\ **Post date:** [April 14, 2016, 3:29am UTC](https://boards.straightdope.com/t/how-do-self-driving-cars-deal-with-stoplights/751031/124 "2016-04-14T03:29:51Z")
> [@usedtobe](#): > > Am I the only one to see the (rather large) problem with Default=On with brakes? > > Zipping down the road at 70 mph is NOT the time for a hiccup causing “Invoke Default”. > > Unless every other pod for the 10 miles behind also slam on the brakes simultaneously. > > Not a good idea. Existing active cruise control systems already understand following distance just fine. Self driving cars wont rear end other cars. You have already mischarachterized my “slow down or stop” into slam on the brakes and come to a screeching stop. There are about 50 shades of grey area in there that the car can utilize, and will on a minute to minute basis. I used amusement park rides as an example of methodology, not identical implementation. [Previous page](https://boards.straightdope.com/t/how-do-self-driving-cars-deal-with-stoplights/751031.md?page=6)