Safe Speed Forums

I've just had an idea, spun off from posts around here: http://www.safespeed.org.uk/forum/viewt ... 5662#95662

We know that traffic lights on roads with 60 and 70mph traffic are, at best, a bit dodgy. That's because 3 seconds - the standard length of the amber - is enough to stop comfortably from a bit over 40mph. No more than that.

So what if the sequence was:

green - go
green+amber - lights changing - be prepared to stop (3 seconds)
amber - stop unless it would be dangerous to do so (3 seconds)
red

That would fix it...

- No change to traffic flow
- No change to amber length
- No expensive 'advance' lights as seen in some other countries.
- Just more warning for high speed traffic

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Around here it would mean

green+amber - Floor it
amber - Floor it you can still make it
Red - If less than two cars have gone through in front you will probably make it because the other direction are expecting you to jump the lights.

This would just be a software/firmware change to the lights I would think. There would have to be a public notice/education program to back up the change. Sounds like a reasonable idea.

Sorry, I don't see the advantage over an amber stage of suitable length.

If amber lengths vary by road type you will NEVER be sure if you have time to go safely before the red.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Alternatively put them on a higher pole so they can be seen from further away? If they change to amber at anything less than your stopping distance away then you keep going so I don't see where the problem is. I wouldn't approach a set of traffic lights in NSL at 60, I'd be doing less than that depending on when I thought they were going to change. The sooner I thought they could change, the slower I would be going so I don't see the issue. As long as there are warning signs before the lights then people know to slow down on the approach. Lights where traffic approaches at speed would have a larger delay between cycles to allow stragglers anyway.

3 seconds braking time would differ according to the vehicle. A bike could stop easily from 60 ot 70 in that time. An HGV would probably be able to stop from 30 so variable systems would have to take account of type of traffic to some extent or be really clever and know when there was an HGV or other slower stopping vehicle was approaching so they didn't change too soon.

If amber always means 3 seconds to red then you know where you are. If they were different according to road speed limit then you could end up with all sorts of problems as people not knowing the change would brake hard and gather the people that knew the amber length was longer. Ditto those that expected a longer amber length would end up running reds.

No one wants to do an emergency stop for a traffic light. If we allow ourselves 0.45g that's a 'comfortable' firm braking effort and applies to most vehicles.

If we are exactly 3 seconds from the lights at present speed when they start to change, we are in a worst case situation - on the cusp between going and stopping. Close and we go. Further back and we have more time to stop.

If reaction takes 0.75 seconds (good and attentive) then we have 2.25 seconds left AT PRESENT SPEED before we reach the stop line. Braking at 0.45g from 44mph takes about 4.5 seconds during which time we cover the remaining distance to the stop line at an average of half the speed we had initially.

Approach faster than 44 mph and we have to brake harder than our confortable maximum is we are to not violate the lights.

Drivers do not know this! And frequently approach lights at 60 or 70mph on roads that appear suitable.

My proposal maintains the standard length of the standard amber and add a 3 second prior warning to give those at high speed more time to adjust. They now have 6 seconds to decide to go or to stop.

I'm pretty pleased with the proposal...

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

From this web site:

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Andrew.

Certainly sounds like a good idea.

Although I wonder if perhaps an even better idea could be to have signs placed a few hundred yards before lights which count down to red, in addition to what you already proposed. I think some countries might already do that.

I've often thought it would be nice to now as you approach how much time you've got left. It's more important now lights have cameras on 'em too.

But how about some kind of count down market so you know where you are in the sequence? Assuming you can see they lights, I think it would be handy to know how long you've got before our light goes green, so you're ready to go when it does go green. It might even improve traffic flow...

I've seen Paul's PR, but I have to say I'm far from convinced, as we have discussed before.

Where I live in the North-West is probably the largest concentration of NSL traffic lights in the UK (including a fair number in 70s) and I'm not aware they represent a significant safety problem. If there is an issue, then I expect the engineers will simply increase the intergreen period. In any case, I don't think I'd normally barrel through at 70 or anywhere near unless they had only recently changed to green - you have to approach them in the expectation they might go red.

If you're not careful you'll have the DfT telling highway authorities to reduce the limit to 40 for 400 yards before every set of lights on a road with a limit of 50 or over

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"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

Sure. But how many drivers know that?



If they did it would be one speed limit reduction that was actually based on some sort of reality.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Here's the PR Peter mentioned, issued at 17:01 today (note embargo):

PR346: Traffic lights: The fast road problem

news: embargo: Not for publication before 00:01am Monday 21st August 2006

The Safe Speed road safety campaign called today for a change in the traffic
light sequence on faster roads. The standard three second amber phase simply
isn't long enough for drivers to stop comfortably from much over 40mph, yet
traffic lights are increasingly common on 60 and 70mph roads.

It has long - and rightly - been considered that the amber phase should always
remain the same length. This is absolutely essential is driver are to be able
to judge if they have time to stop when the lights change.

But a 3 second amber on roads with 60mph or 70mph traffic does not allow
drivers sufficient time to stop comfortably. Red light violations are likely to
be much more frequent on high speed roads as drivers are caught out when the
lights change.

At Safe Speed we have long been concerned about the problems, but have now
devised a complete and original solution that requires no new traffic light
hardware. We simply need to add a green and amber 3 second 'change warning to
the existing sequence. The new sequence becomes:

GREEN Go if safe
GREEN + AMBER (3 seconds) Prepare to stop
AMBER (3 seconds) Stop if you can do so safely
RED Stop
RED + AMBER Prepare to go
GREEN Go if safe

This could be fitted to most sets of traffic lights with a simple, low cost
software change. The extra three seconds of warning is a vital safety measure
for traffic lights installed on faster roads. The new scheme would also require
a public information campaign.

Paul Smith, founder of the Safe Speed road safety campaign
(www.safespeed.org.uk) said: "We have long been concerned that 3 seconds of
amber simply is not enough on faster roads. Fortunately we have found a
complete solution and trials should start without delay."

"Department for Transport is far from 'on the ball' with road safety matters
these days and it is really quite astonishing that it falls to organisations
like Safe Speed to solve these sorts of problems."

"It's a simple matter of a quick and complete solution to a genuine public
safety issue."

"Until we get some changes, the least we can do is warn drivers that
approaching a set of traffic lights at much over 40mph simply isn't safe."

<ends>

Notes for editors
=================

Facts and figures.

The 'worst case' is being three seconds away from the lights when green changes
to amber.

A B C D E
40 59 176 120 163
50 73 220 175 241
60 88 264 240 333
70 103 308 315 441


A= Speed in miles per hour
B= Speed in feet per second
C= Feet in 3 seconds (worst case distance from traffic lights)
D= Highway code emergency braking distance in feet
E= Comfortable firm braking distance in feet, Calculated from 0.45g
deceleration and 0.75 seconds thinking time.

It is not wise or appropriate to rely on doing an emergency stop if the lights
change.

The maximum safe approach speed to a set of traffic lights that may change is
calculated as 44mph (0.75 seconds thinking, 0.45g braking, 3 second amber). A
better message for drivers is '40mph'.

Highway code stopping distances:
http://www.highwaycode.gov.uk/09.htm#105

Safe Speed braking calculator spreadsheet:
http://www.safespeed.org.uk/braking.xls

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

But, as I said, the "solution" is to increase the intergreen, which has the effect of the change you propose without introducing a new light phase that many drivers (e.g. those in Central London, or in Northern Scotland) might never experience.

_________________
"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

I'd be happy with that, except don't we just know that they would be adding cameras to catch drivers out. On a wet day, I expect you could catch loads.

Isn't it better to get the information out there being discussed so at least drivers have a fighting chance of KNOWING the problem?

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I've linked to this before, I think:

http://www.sabre-roads.org.uk/forum/vie ... hp?p=29794

but our signals engineer friend doesn't see that with the range of control mechanisms available to him there is, in reality, any problem.

_________________
"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

But think of all the inexperienced drivers - who have absolutely no idea that traffic lights require them to reduce speed way below the posted limit. Throw in a wet day and the appearence of ambe is quite likely to result in vehicles skidding with far from predictable results.

I simply cannot see how drivers are equipped to cope.

I quite appreciate that the all red phase can make cross traffic risks go away, but surely the loss of control risks (under braking) are a very real feature.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I honestly think this is a largely theoretical problem that doesn't really apply in practice.

If, in the real world, it led to significant numbers of collision or loss of control accidents, then I'm sure something would have been done about it.

_________________
"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

Only problem I can see with your PR, Paul, is that after reading this...



some people might interpret that as, the 60/70 limits are too high and should be reduced to 40/50.

True - but if 60mph really is too fast when the lights change, then that solution - for once - falls into the category of sensible.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

The theory is pretty clear. I'm confident that if we actually looked for the problem in the real world we would find it. I'm also confident that many (if not most) drivers do not slow down from 60 or 70mph for a green light that may change.

Anyway, if he only thing that comes out of this is that the situation is considered and monitored, then I'll be happy.

But I take your point. I have no evidence that it's anything other than a 'theoretical' problem.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety