Legalities of traffic light phasing

[funkyrobot]

Hello all,

just a quick question.

Is there supposed to be a certain length of time where one set of lights at a T junction changes to red and another set turns to green?

Just wondering this as a junction near me has terrible phasing. One set of lights goes green as another flicks to red, therefore cars seem to be passing through the junction as other cars set off. I think there may be an accident waiting to happen here.

I have put in a complaint about this but to no avail so far!

Cheers all!

[GreenV8S]

funkyrobot said:

Is there supposed to be a certain length of time where one set of lights at a T junction changes to red and another set turns to green?

I believe there is a standard minimum inter-green interval between conflicting traffic streams.

[Burgmeister]

i say get rid of the barstewarding things entirely. traffic always flows better when they break. so what if its more risky!

[tvrgit]

Are you suffereing memory loss? You asked about traffic signal phasing in this thread in August, and various opinions were put forward.

http://www.pistonheads.co.uk/gassing/topic.asp?h=0&f=10&t=426975&i=0 

My answer now is the same as it was then (because I was right then and the regulations haven't changed), and I'm sorry but I can't be arsed to type it all out again.

Edited by tvrgit on Sunday 16th December 18:46

[funkyrobot]

tvrgit said:

Are you suffereing memory loss? You asked about traffic signal phasing in this thread in August, and various opinions were put forward.

http://www.pistonheads.co.uk/gassing/topic.asp?h=0&f=10&t=426975&i=0 

My answer now is the same as it was then (because I was right then and the regulations haven't changed), and I'm sorry but I can't be arsed to type it all out again.

Edited by tvrgit on Sunday 16th December 18:46

Very sorry, I don't get much time on here anymore and I didn't check back to my old post properly.

Thanks for pointing this out, silly me!

[Burgmeister]

funkyrobot said:

tvrgit said:

Are you suffereing memory loss? You asked about traffic signal phasing in this thread in August, and various opinions were put forward.

http://www.pistonheads.co.uk/gassing/topic.asp?h=0&f=10&t=426975&i=0 

My answer now is the same as it was then (because I was right then and the regulations haven't changed), and I'm sorry but I can't be arsed to type it all out again.

Edited by tvrgit on Sunday 16th December 18:46

Very sorry, I don't get much time on here anymore and I didn't check back to my old post properly.

Thanks for pointing this out, silly me!

oh you silly little thing you

[7db]

I can't believe tvrgit killed off the thread before JustinP got a look-in...

[tvrgit]

7db said:

I can't believe tvrgit killed off the thread before JustinP got a look-in...

all part of the service

[Dwight VanDriver]

Any comment on optimum timing to effect max flow from green to amber Tvrgit?.

Seem to remember reading something in the past that 40 secs provided the best flow.

Appreciate things could change dependent on traffic flow patterns.

dvd

[tvrgit]

Dwight VanDriver said:

Any comment on optimum timing to effect max flow from green to amber Tvrgit?.

Seem to remember reading something in the past that 40 secs provided the best flow.

Appreciate things could change dependent on traffic flow patterns.

dvd

Jees DVD, that's a corker!

There are a lot of variables to take into account: traffic flow on main road / side road, how many are turning (they go slower) compared with straight ahead, what proportion are HGVs or buses, gradient, visibilities, etc. Thge green time will vary from junction to junction and might be different in the morning peak or evening peak, or at weekend near shopping centres etc.

Basically for each road (or each lane if the lanes do different things) you work out the saturation flow - ie the number of vehicles that would get through in an hour if the lights were green all the time - normally about 1800 per hour or one every 2 seconds or so.

Then you divide that into the actual counted flow on that arm to get what's called a "y-value" - so if there are say 600 cars going through on road A, and the sat flow is 1800, then y=0.3. You use the y-values to calculate what proportion of the available green time in any cycle each road gets.

The trick is working out the optimum cycle time to minimise delays - that is dependent on the y-values and the "lost time" (ie the time that traffic isn't moving) - longer lost times mean longer cycle times and longer queues.

There are, of course, computer programs to make these calculations easy - and easy to get wrong if you don't understand the principles!

It's not too hard to understand but I think, very boring. I'd be happy to explain in more detail if people are interested enough.

[Dwight VanDriver]

Obliged.

Wiser?

a little bit.......

dvd