New call for traffic light changes
More warning on fast roads needed, says Safe Speed
Fast roads need more stopping time
The standard three-second amber phase simply isn't long enough for drivers to stop comfortably from much over 40mph, argues Safe Speed, yet traffic lights are increasingly common on 60 and 70mph roads, broadening its traditional focus on speed cameras.
Safe Speed reckons that it has long -- and rightly -- been considered that the amber phase should always remain the same length. This is essential so driver can judge if they have time to stop when the lights change.
But a three-second amber on roads with 60mph or 70mph traffic does not allow drivers enough time to stop comfortably, argues the campaign. Red light violations are likely to be much more frequent on high speed roads as drivers are caught out when the lights change.
Safe Speed said: "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 three-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, according to the campaign. 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.
Technical details
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 |
Key
- 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.
Comment
Campaign founder Paul Smith said: "We have long been concerned that three 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."
Links
If I'm in a 70 limit approaching lights and lets face it I'm probably going much quicker, I (as any one shoud do) start to decelerate even on a green light as I need to know that I have enough time to break hard should the lights go to amber and I'm border line on clearing red, and/or there is an emergency vehicle about to jump the lights. A green light does not really mean go, it's proceed if clear.
Learning to drive properly linked with better anticipation and hazard awareness is a better approach rather than messing with standard thigs such as light sequences.
Mark
Personally I don't think we should be adding in extra steps in the sequence - we don't want the average ignorant motorist confused any more than they are already!
JJ
Paul is right to show that you can only stop comfortably from 40mph in the 3 seconds that you have, but most drivers don't slow for green lights. This combination does tend to push drivers toward a dangerous choice between an emergency stop or a ticket.
I doubt most drivers even realise that all the lights spend the same time on amber - I'd make it longer in line with his calcs.
The essence of the problem is that if you are driving a "Highway Code" vehicle (ie one that brakes to the Highway Code standard), then at a critical speed, there is a stretch of tarmac that you could be on (at the moment the lights change to amber) from which it is difficult orimpossible to stop for the red light. The higher the speed, the longer that stretch of tarmac.
If I've read the maths correctly:
- For comfortable stopping (using Paul's 0.45g deceleration), the speed is about 44mph
- For emergency stopping (as per the Highway Code), the critical speed is about 65mph
- Between 44 & 65mph, drivers must perfom a major to emergency stop. At 70mph, drivers in a strip about 130' long will need to brake harder than is comfortable.
- Above 65mph there is a strip of tarmac on from which it is impossible to stop. At 70mph, that strip is already 7' long
So, if lights are installed on a road with a speed limit above 65mph, you can be legally going about your business, and then break the law by crossing a red light. That in itself would make for an interesting legal defence.
Even at 50 or 60mph, the risks of an accident are increased (even though eveyone is acting within the law) as some people will be performing harder braking than normal. And of course, being at a set of lights, this will be happening rather frequently.
From Paul's own figures, a 4-second amber at 50 & 60mph, and a 5-second amber at 70mph would completelty resolve this problem, and so make lights on higher speed roads considerably safer.
On the green-amber issue, Paul actually has a point. We all intrinsically know that the amber light is on for about the same amount of time wherever we see it, and use that assumption as we decide whether to stop or carry on, and how hard to brake. Changing the length of time would screw with our mental calculations at every set of lights everywhere - you would still have people panic/over-braking at these long-amber lights, and you would have people overrunning on the old short-amber (I hope that makes sense without a page of explanation). Overall, that would be just as dangerous, potentially worse.
So the options would be:
- A warning sign that this is a "long-amber" light
- A mark on the road for the "critical stopping distance"
- Paul's green-amber pre-warning
- Ban traffic lights on all high speed roads
- Impose a blanket 40mph limit at every set of lights.
And in that context, it's probably the best option.
But should I delete the last option, in case someone at the DoT thinks it's realistic?
I think just changing the time is not enough because if it goes to amber then you may believe that you only have 3 seconds and so stop aggressively anyway and confuse on normal lights.
Changing the sequence also has risks and although preferable I think highly unlikely given the driver education costs.
Possibly best is an additional set of flashing lights (like on a level crossing), set further back from the junction that flash just before lights are due to turn amber.
PS. I always prepare to stop anyway because the b*****d things usually turn to red once I approach them!!!
followed by my face, on most occasions!All of that said I don't see it as a problem and I regularly drive along a road leading out of Bracknell onto the A322 which is 70 past some lights.
Edited as I'd spelt Bracknell with a lowercase b and it's offended Slowly Slowly... my sincerest apologies sir.
I'd go with increasing the duration of the amber light according to road speed limit and location. Nothing worse than someone slamming on the brakes just before the line so as to keep legal.
A dotted line at a distance to use to judge where you are NOT going to make it from might be worth a trial.
"been considered that the amber phase should always remain the same length. This is essential so driver can judge if they have time to stop when the lights change."
Then I thoght about the set of lights where a Monitron Speed & Red Light Camera was tested on an NSL dual carriageway where the amber timing was reduced to 2.3 seconds. Making matters worse the camera was on a hair trigger as far as the RLC aspect considered, one wheel revolution over the white line any time during red light and it flashed. Fraction of a second before green on red& amber and it went off. Speed setting I have no idea but it brassed off a lot of people.
Nobody knew the camera was only under test!
Safespeed is 110% correct to raise this difficult concept, plus 120% correct to say at this moment in time it is unwise to approach any green light at much above 40mph, especially if you can see that the light has been green for some time and there are vehicles waiting on potentially conflicting routes.
Not sure about varying the sequence, varying amber timing which I suspect they already do for benefit of revenue (cynical mode) is also dodgy without some sort of additional signage. Maybe an early warning flashing sign on fast routes, bit like the wig-wag level crossing signs?
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