Stop lights

[Louie's gone fishing]

If stop lights worked more effectively would we save on fuel used?

When I driver to the store I use a route based on avoiding the stop lights. If I go the shortest way, 1.8 miles I hit five lights and have never, ever gone through without hitting at least three, never, no matter how I try to pace it. If I go the ‘avoid stop lights way’, its 3.2 miles and it’s faster. The stop lights get you even if there is no traffic. You have to wait for all the cars that are not there to not get through the intersections. When there is traffic you sometimes don’t make it through if you are over six cars back which happens. At one intersection you often can’t go because cars going the other way don’t make it through and are out there blocking you. It is also dangerous because other drivers don’t want to be caught and they more than cut it close. A local Sheriff told me they average one bad accident a month and several fender benders in between. He said his criteria on running an amber light is first speed and then if the driver speeds up to beat it. He said if it’s kind of close and the driver cruises through at or below the speed limit he is likely to ignore it if the traffic is light. Anyhow, I was just wondering if light that works better would save gas and fenders.

 

[Tosh]

Yes, but until now gas prices haven't been high enough to justify spending the manpower to plan traffic and program the lights better.

 

[brianl703]

Sometimes I think they spend the manpower to figure out how to slow drivers down. Getting stopped by 5 traffic lights in a row doesn't happen unless someone in the DOT configures the lights to make it happen.

On the other hand, it could just be incompetence.

 

[The_Jeff]

They program the lights for whatever priority they have.

In manhattan for example, going "the long way" is synchronised while going perpindicularly isn't.

Money and politics are often involved. A rich, connected neighborhood will want traffic to detour, then the people suffering the detour try for lower speed limits and lights as well. It's a race to the bottom with speed bumps, cops everywhere, etc.

 

[ccs v2.0]

Originally Posted By: eljefino
Money and politics are often involved. A rich, connected neighborhood will want traffic to detour, then the people suffering the detour try for lower speed limits and lights as well. It's a race to the bottom with speed bumps, cops everywhere, etc.

Far too often. I find that the state of repair, size of the roads and even state of development, are inversely proportional to the neigborhood's affluence.

 

[OriginHacker21]

All of the lights on my street used to be synchronized - they'd turn red even at 1:00am. Only way to beat them was 20mph over the speed limit. Last year they installed sensors on the stop lights so they are green unless someone comes up. So when I get up at 4:00am and head to work - green all the way down to the freeway.

Yes, it is beautiful. Now, try driving a small compact that doesn't get the lights to change until an SUV comes and makes it change.

 

[01rangerxl]

I think proper stop light timing could do a lot to reduce fuel waste, but in some rapidly growing areas the population just keeps rising. I have heard that properly timing a light costs a lot of money. If that were done frequently to compenstate for a rapidly growing population, it could become a huge expense.

I wish Charlotte would change the timing on some of their lights. Many of them have very long waits, even when traffic is very slow.

 

[Gary Allan]

Our borough's lights are all asynchronous and not very precise. You may hit the same red light from another for 5 months ..then find that you can pick up the pace and make it for 3 months ..slow down and make it for 4 more ..etc..etc.

We have one cross street that has a really long light for no good reason. This is in a town that should just have flashing yellow=red lights after 9-10pm. They even have the pedestrian WALK/DON'T WALK (with both directions RED) still functional in a town that may have 2 people over the full span of downtown at any one time after 10pm.

 

[oily boyd]

Not really a light timing comment but I appreciate that when I have been to Delaware, OH (near Columbus) in some 55 mph zones, they have a warning signs/lights about a quarter mile from the traffic signal.

If the warning sign is flashing, you know there's no way you're gonna make the upcoming signal.

It probably sounds silly to someone who's never seen it but I appreciate knowing ahead of time whether I can simply maintain speed or start coasting and save my brakes.

 

[Louie's gone fishing]

I've wondered how tough it would be to really coordinate lights. I guess it would be too much trouble because it would take a plan that no one would agree and it would take action on the part of someone to choose one plan among many and with city business the way it is it’s probably better to let a committee decide that all together they can’t decide. Committee’s can’t really get anything useful done even though traffic lights would offer a savings if they were controlled a bit better. One thing they do with lights is that when enough children get killed or crippled at an uncontrolled street crossing in a neighborhood, they will finally put up a stop light. The politicians can claim they spent the money on a good cause and will have the body count for justification.

 

[sciphi]

Out in the 'burbs delivering pizza (not as much money as 6 months ago, let me tell you), I go through a lot of lights. Most of them I can see from about 300 yards away and adjust speed accordingly since everything is so spread out. That may mean I drive 45-50 in a 55 or 35 in a 40-45. I save gas by not going as fast, and not having to stop at a light. People get [censored] until they see the light and realize they didn't have to touch the brakes.

 

[brianl703]

Originally Posted By: OriginHacker21
Last year they installed sensors


Oh wow. It only took them till 2007 to start using technology that was around in 1977.

All of the lights around here are on sensors and have been since at least 1988 when I moved here.

 

[brianl703]

Originally Posted By: Gary Allan
Our borough's lights are all asynchronous and not very precise.


I've noticed that. I found a company that sells a device that retrieves the time from the GPS satellite and syncs the clock in the signal controller with it.

The signal controller has an RS-232 port and a text-based user interface. The GPS device connects to the RS-232 port and enters the commands to set the clock once per day.

VDOT has connected leased lines to all of the RS-232 ports in their signal controllers in the Northern VA area which allow them to keep the clocks in sync and also to make configuration/timing changes remotely.

A cash-strapped locality could stick a dialup modem and a $20/month telephone line on each of the RS-232 ports of their controllers. Then they could use a $50 PC running a Perl script (under Windows or Linux) to dial into each of them once a day to set the clocks.

Of course if their controllers are too old to have RS-232 ports that's another problem. Most ones made since, say, 1985 do.

 

[brianl703]

Originally Posted By: Louie's gone fishing
I've wondered how tough it would be to really coordinate lights. I guess it would be too much trouble because it would take a plan that no one would agree


Most coordination schemes have 4 timing plans:

AM peak, midday, PM peak, night.

AM/PM peak timing plans are set to favor the direction the commuter traffic is going.

Midday timing plans are usually set to favor both directions as equally as possible.

Night timing plans usually aren't. That is, at night, the signals operate in "demand" mode where they change based on input from the sensors. A typical setup for a side street on a major arterial has sensors right at the stop line on the side street, and sensors up to a few hundred feet back on the major arterial (depending on speed limit).

At night, when someone pulls up to the stop line on the side street, the controller checks for traffic on the major arterial and if none of the sensors indicate that any traffic is approaching (called a "gap out") it will change to yellow and red for the major arterial and then change to green for the side street, until the side street traffic is cleared. The sensor for the side street extends the green time a few seconds each time it detects a vehicle (this is also usually true for left-turn lane sensors), until the maximum programmed green time for the side street has been reached. Then the side street gets a yellow and then red and then the major arterial gets a green.

This can become slightly problematic if someone's car breaks down on the sensor or (as I've seen a few times) a cop who doesn't know any better parks their cruiser on the sensor. This causes the sensor to always detect a vehicle which causes the traffic signal to waste time giving a green that will not be used.

Also, sensors can and do fail. When they do they usually fail "on" so that they appear to always be detecting vehicles. This is why you might see a traffic signal give a left-turn arrow when the left turn bay is empty. If you see this, you may want to give your public works department a call and let them know they might have a failed sensor. Often they have no ability to remotely verify the operation of the controller so the only way they know there is a problem is if they routinely check (yea, right) or if someone complains.

Oh yes--what happens in demand mode if the arterial has so much traffic it never "gaps out"? Then it "times out"--after giving the arterial a certain configured amount of green time without seeing any break in traffic then the controller will change to yellow and red for the arterial (to give the traffic waiting on the side street a green) anyway.

It's considered bad to have a controller continually timing out on an arterial--if the traffic is that heavy it should probably be on a timing plan, not running in demand mode.

 

[brianl703]

Originally Posted By: OriginHacker21

Yes, it is beautiful. Now, try driving a small compact that doesn't get the lights to change until an SUV comes and makes it change.

Well, it took till 2007 for them to implement what had been around for over 25 years, at that rate I would expect them to get it working right by 2020 or so...

 

[oilyriser]

Amory Lovins will have fun trying to drive his carbon fiber Hyper car, in a town that uses lots of sensors. I bet a loop of wire strung around the car with a strong a/c current you could switch on would activate a sluggish ground loop sensor.

 

[mechtech2]

They really are trying to make this better. Sensors in the ground at the light and in the roads elsewhere are becoming common.
I notice when there is light or no traffic, many lights change earlier to speed things up and keep things moving.
Also, allowing a left turn on red is almost universal in the US now.

 

[XS650]

Originally Posted By: brianl703
Sometimes I think they spend the manpower to figure out how to slow drivers down. Getting stopped by 5 traffic lights in a row doesn't happen unless someone in the DOT configures the lights to make it happen.

On the other hand, it could just be incompetence.


Never underestimate the power of incompetence. Or not giving a chit.

 

[XS650]

Originally Posted By: brianl703
Originally Posted By: OriginHacker21

Yes, it is beautiful. Now, try driving a small compact that doesn't get the lights to change until an SUV comes and makes it change.

Well, it took till 2007 for them to implement what had been around for over 25 years, at that rate I would expect them to get it working right by 2020 or so...



Done right, they work very well with motorcycles and tolerably well for bicycles.

 

[oilyriser]

some places are testing machine vision systems