New call for traffic light changes

More warning on fast roads needed, says Safe Speed

By PH Staff / Monday, 21 August 2006 / Loading comments

Fast roads need more stopping time

A road safety campaign has 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, 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."