What if all cars at a stop light allowed enough space between them and the car in front to all go when the light turned green? Yes they would be spaced farther back but the time saved would cancel out the difference and more cars could get through the light
I’m not sure if it would work in theory, but in practise, unless all of the cars actually did start at the same time, failure of one care to start would propagate to the rear causing all the cars behind it to stop anyway.
I say this from experience because even when I am the second car in line, the car in front of me rarely starts at time I would like. I’m sure there are some times when I do not start soon enough for people behind me. So unless everyone was synched perfectly, you’d still have a delay.
There’s also the problem that not everyone accelerates at the same rate.
There’s always at least one who’s not paying attention or feels that letting the engine pull itself from idle is fast enough.
I haven’t got any computer projections or mathematics to back me up in this but I don’t think it would be any quicker. What happens now is that cars queue up and a concertina effect causes a gap to appear between the cars after they get up to speed. Your suggestion is that the concertina effect should remain when we queue at the lights. At best then, the gap remains the same. At worst, human reaction times causes the spread to get even longer and possibly even backs the traffic so far back it starts impeding the progress of traffic at a set of lights behind.
That’s true. Probably my manual transmission has something to do with my faster acceleration. That and living in a huge retirement city.
Whenever gas prices get high, a larger number of people turn to all the tricks to save on mileage, one of them being putting your foot very gingerly on the accelerator. And some people do this all the time.
There’s no way this could work in practice. Eventually you start having some cars sit through a second or third red light. Bunching cars is actually a good technique.
When I see a red light ahead of me, I always take my foot off the gas and coast to maximize my chances that the light will turn green before I get there. I’ll even brake a little. I was taught that you are better off at even 10 miles a hours than trying to accelerate from a dead stop. You do have to keep your eyes open for people behind you that are signaling for a left turn and may need to get to the intersection sooner.
The exception is lights that are controlled by sensors that won’t cycle unless it detects a waiting vehicle. If there is already a car waiting, then you are okay, otherwise you need to know if the intersection has sensors or not.
If you do time it perfectly and don’t have to stop, then watch out for cross traffic. I would have been killed by a cement truck running the red light if I hadn’t been paying attention earlier this year. I was sure glad I had my brakes serviced a few months before.
With the gap technique, think about the cars behind the first: After the light turns green they are driving over pavement they would have otherwise crossed while it was still red. How is that saving time?
To really save time, the first car should stop at a distance from the light and the green light should go while cross traffic is still clearing the intersection. If it’s timed right, the whole line of cars enters the intersection at full speed just as it clears and there is little or no “dead time”. Of course that would be very unsafe and there would be many accidents.
If there were such a thing as a central traffic control system able to communicate with and control all the cars, it would run them in pelotons at max speed through the intersection. Between intersections the peloton would be slowed down and spread out and then regrouped and sped up in time to hit the next green light.
You’re forgetting about what happens before the cars come up to the light. With your system, I’d have to brake harder in order to stop in a shorter distance instead of using the momentum I already have to get closer to the light. That’s not going to save time or fuel.
I’ve thought about this, too. Perhaps a more doable scheme along these lines is to have several sets of sensors starting wayyyy back from where you have to stop. Then, if it would change anyway under the old sensor configuration, it will be able to instead turn just as you need it.
Plus, these sensors could determine when traffic is not flowing on high traffic roads. So if you are waiting at a cross-street and there is no traffic on the main street, it can let you go instead of waiting through the whole cycle.
While I spend a lot of time and gas sitting at traffic lights, the times that truly annoy me are when I am sitting there with no cars on the other street.
JoelUpchurch has a point, with getting off the gas when you see a red light ahead. The other end is also helpful; the concept of “stale green.” If the green light ahead has been green for quite a while, you can get a feel for whether it will go red before you get there. If it is stale, get off the gas.
In a series of synchronized stoplights, the ideal speed is less than the speed limit. If the limit is 30, and you have just gone through a light without stopping, you can make the next several if you keep your speed at 27.
You can save fuel whenever your foot is on neither the gas nor the brake. Braking wastes fuel you already used to get to that speed.
I hear you, Brother. I’ve gotten in the habit of turning off the engine and coasting up to intersections if I know I’m going to be sitting there a while.
I’m anticipating the day they put cameras at all the intersections and hook them up to a system smart enough to recognize cars, bikes, and pedestrians and run the signals accordingly. Any one at Google looking for a project for your 20% personal time? This seems way more practical in the near term than self-driving cars.
I was pretty much going to mention this, you’ll end up making things worse. Let’s look at the two extreme versions. Let’s imagine a car needs ~ 25’ when stopped (with no spacing), and 100’ when travelling at the speed limit for that road. With only two cars, the second car either starts from ~25’ back a split second later, or starts from ~100’ back at the same time. Which one gets to the light first? Clearly the one that was closer.
Now let’s look at the other extreme 50 cars fit in roughly a quarter mile with that now, or if they have to maintain the distance, that last car is roughly a whole mile back. Even if you assume no accelaration variable (assuming either car gets to max speed in roughly the same time and witin that quarter miles) and thus that 3/4 mile difference is covered at highway speed, that’s still 45-50s to account for all those split second differences which, at best, leaves it roughly equal.
And, of course, all that assumes that with the constant distance, everyone could start at roughly the same time, which just won’t happen. So, once you throw that back in, leaving the distance constant not only takes more time, but it wastes more road space.
Here’s a good toy to help you intuitively see (use the traffic light one):
http://vwisb7.vkw.tu-dresden.de/~treiber/MicroApplet/
You’ll notice that with the traffic light, even though some traffic stops, once it starts, the condensed traffic way lightens as it works it’s way back and eventually disappears so that new traffic doesn’t slow down at all. If everyone back to the next gap in traffic would have to stop simultaneously, which clearly makes the former case superior since the former case never falls below the needed throughput, where the latter necessarily does.
This would imply that the latter case would approach the former case if the throughput of the light is insufficient for the traffic demand, but it would never surpass since it would always result in everyone stopping, where the former case doesn’t.
About 20 years ago they ran a trial system on a road in Melbourne, where electronic road signs would tell you what speed to go in order to reach the next intersection when the light was green.
They’d never tell you to go faster of course, the recommended speed was always lower than the limit. Usually quite a lot lower, so everyone ignored them. They’ve been gone for years now and I haven’t heard anything about it since. There might be some info about it on the net but I wouldn’t know what to search for.
In my area of SE Michigan, the lights are synchronized, kind of, but it generally only works if you do about 5 mph over the speed limit, and everyone else (or at least one lane) also does about 5 mph over the speed limit. Generally, though, we do about 15 to 25 mph over the speed limit on the freeways, and surge on surface roads. Meaning, take off at a green light, go about 15 mph over the limit, and then brake at the next light. At the very second you’ve achieved a complete stop, the light turns green.
I do that too. To be most effective, you have to not only know how long the particular traffic light cycle is, but also be able to estimate roughly where it is in the cycle. Which means you have to look at which lanes currently have the right of way as well as how many cars are waiting in various lanes.
There are such systems in development. There may even be some installed somewhere as a pilot project.The main difficulty is recognizing vehicles and pedestrians in all sorts of lighting and weather conditions. Trivial for most humans, but not an easy task for computers. If they ever get good enough, they could largely eliminate the yellow-light part of the cycle in low traffic situations.
I advocate this on the basis of time efficiency and frustration reduction, though presumably anything which reduces idling and overall trip time will help fuel efficiency.
In effect that’s what happens all the time now, when everybody pulls up to the bumper in front of them and fails to allow this starting-space. And it’s cumulative: the second car must wait for the first, the third must wait for the first then the second, the fourth must wait for the first then the second then the third.
The key is that you don’t start really accelerating until the vehicle ahead has picked up a little speed and the gap has grown. Everybody who can see the light can still start rolling at the moment of green if there’s room in front.
There have been ideas thrown around in the auto industry where stoplights will send an RF signal (or something) to on coming cars when the light is about to turn yellow/red. The car would receive this signal and the brake would automatically apply. I don’t like this idea, but I’ve heard about it.
Did this OP originate from Marilyn’s column in Parade this week?