Over on Transterrestrial, there was a discussion about self driving cars eliminating traffic jams. The site doesn’t allow comments from my computer calling it through a proxy, so I’ll just throw out a few thoughts here.
The discussion focused mostly on cars accelerating from a red light and the amount of time saved when/if they all accelerated together as soon as the light turned green. Some felt that a lot of time would be saved, and some felt that the computer would have to wait for a safe braking distance just as with a human driver with the only savings being a few seconds here and there.
I saw no discussion of timing the lights that some of us do a bit of already. You see a red light in the middle distance and slow enough that it should turn green by the time you get there. So you might be driving 20 mph in a 30 mph zone by the time you reach the now green light. However, you are doing 20 mph through the light when the hurry up and stop drivers are still accelerating from zero. If done right, it is a faster and smoother trip using less fuel and much less wear and tear on the drive train and brakes. By missing this possibility, many people will be in the same position as the composite people that treat their product as black aluminum and fail to get the potential performance gains possible.
With self driving cars it seems likely that the car will know when the light is going to turn green, and if cars coming the other way are likely to do something stupid. It will also be plugged into the local traffic management systems so as to know the speed the lights are timed for. Many places have had their lights set up in such a way as to allow drivers to hit continuous green lights as long as they maintain some exact speed.
With self driving cars interacting with each other there will also have to be early fault detection systems such that cars with problems can be allowed for and given room to recover, pull over, or get out of the way so that the rest can maintain a steady flow. Follow distance with fault detection could be drafting close even at highway speeds.
So my thought is that a mature system of self driving and interacting cars interfaced with traffic control systems will have a flow pattern occasionally glimpsed but seldom maintained. Cars in city traffic will cluster at a speed that allows them to all get through the green light without stopping at all. I timed a light today that had a minute of green. allowing 2 seconds of margin on each end would give 56 seconds of full flow under the control systems I think likely. 56 seconds of cars with a 30 foot spacing center to center at 30 mph would put over 80 cars per lane through one green light, theoretically of course. That is at least 4 times the number I normally see get through per light change.
I think the focus on red lights missed the possibilities of the green lights. I think many of us are going to get blind sided by, not the technology itself, but the way it changes the way we operate. I tend to believe this extends to space far more than we would like to admit.
johnhare
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As long as there are human-driven cars you can’t do that because someone could run the red light. And once there aren’t human-driven cars, you don’t need lights anymore. The cars will just be spaced apart to miss each other.
I agree Brock. Cost of traffic control infrastructure could drop while becoming more effective. The theoretical handling capacity of our streets compared to the actual traffic shows a lot of room for improvement.
More efficient use of the roads could possibly lead to far less road construction.
Some parts of the world (India, Ajman in UAE for examples) have counters on the lights showing the time to the next change, green to red and red to green. Even the counter changes colors and flashes as it hit 5-3 seconds before the changes.
I think it was introduced to stop people in India getting impatient and attempting to go before the green. However, it does mean when the light changes to green there’s no delay in cars moving (I seem to remember there’s no amber on Red->Green changes) so saving a 3 seconds each light change and maybe more as people ‘get ready to move’.
I’m surprised it’s not been adopted elsewhere, though some may say it triggers red light rush as it counts down and is therefore dangerous, but this happens anyway with amber lights, flashing green lights and just people seeing it’s been green a while so speed up a little.
Would be too much to have the light broadcast the countdown on some low powered local frequency so could be used by self-drive vehicles and other advanced cruise-controls.
mean’t to say “Wouldn’t be too much effort to…”
Of course for a car, smart or otherwise, to time the traffic lights it helps if the lights at adjacent intersections are synchronized. Which would help even with human drivers.
I have occasionally been able to take advantage of synchronized lights. Only occasionally though as many drivers tend to hurry up and wait at the red so you are blocked from the right speed.
Stop-and-go from unsynchronized lights becomes less important in electric vehicles with regenerative braking.
In some districts they time the lights so you can hit green after green. In others, they time them so that you can’t possibly hit the next green, I’m not sure why, but I’ve heard it’s to prevent a certain level of speeding where you can hit a multiple of the normal cycle. In other areas, such as the city where I live, the lights don’t have a default timing they adhere to, they react to traffic detected by sensors. Which is very nice since you no longer spend a minute staring at an empty intersection and a red light, but would make a smart traffic grid a more robust, but more difficult to implement, solution.
On the evolution away for signals at all, I’ve been frustrated watching the self-driving technology progress without any kind of car to car or car to city networking, just driving using the lines and signals as seen by cameras. We’re setting ourselves up to delay actual integrated smart cars by a generation as we “can’t make the existing smart cars obsolete…” and “why would we develop networked cars if while there are still manual and first-generation cars they have to interact with so the benefits are so small…”
Red lights create gaps in traffic important for unsignalized left turns and merges into traffic. (A possible reason to not want all signals synchronized at present.)
Check out the videos here to see the logical (and terrifying) extreme of an autonomous intersection.
This would obviously require that a human driver be strictly forbidden. (Driving manually would be the sort of thing for which Larry Niven would have sent you to the organ banks, back in the day…)
David, making the vehicles fully networked also injects vulnerabilities to malware. Yes, a networked system can be very efficient- but in the wrong hands, also very lethal.
Doug, it’s not just malware you have to worry about with network-dependent vehicles. Everything has to be able to work in an outage, or even with a severely degraded network. Getting telemetry to and from a whole bunch of cars at once with extremely high reliability and low latency is a really, really hard problem.
Brock says: As long as there are human-driven cars you can’t do that because someone could run the red light. And once there aren’t human-driven cars,
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The obvious thought is that certain lanes, streets and intersections could be autonomous vehicle only; this would benefit all drivers as the auto-only network would be able to handle a higher level of traffic, reducing the pressure elsewhere.
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Also, rather than focusing on travelling faster, having a smooth safe ride home would allow for the return of dining cars: take the long route but enjoy breakfast/dinner on the way. Cars could be designed around a central table, also allowing board games etc, but given the rents in CBDs, restaurants may find it practical to have modified buses offering fine dining for commuters.