Dangerous variable speed limits on M4 Newport

Lum

I think you're supposed to use local roads to get to J26 rather than joining westbound then immediately going through the 2 lane tunnel, or going through said tunnel eastbound then immediately exiting. Should reduce a little bit of traffic in tunnel in theory, and we all know it needs as much traffic reduction as possible.

Still a bit of a half hearted attempt though, if you're going to do that sort of thing you should also be removing bidirectional access at J26 and then you could just call J25A part of J26. Chances are the local road network in that area couldn't take it though, or they couldn't actually agree on a plan, so we got this half finished job instead.

If you have too many junctions on a motorway then it tends to pick up too much local traffic which contributes to congestion, e.g. M6 J3-J9. The brynglas tunnels are the last place we want that to happen.

Lum

Ok, I think I know the sign wig is complaining about now. You come around a fairly tight bend and the sign only comes into view about 100 metres away.

Personally I think there's enough time to slow down to 50 upon seeing it without slamming on, providing that you happen to be looking ahead at the time they come into range. In any case that particular gantry doesn't have cameras on it.

I suspect a lot of it would come down to how that gantry is used. Certainly switching it from blank straight to 40 would cause problems as people close to it panic and slam on while still on what is quite a sharp bend for motorway standards. Providing they ramp it down 60, 50, 40 it should be fine.

Wig

Lum wrote: »

Ok, I think I know the sign wig is complaining about now. You come around a fairly tight bend and the sign only comes into view about 100 metres away.

Personally I think there's enough time to slow down to 50 upon seeing it without slamming on, providing that you happen to be looking ahead at the time they come into range. In any case that particular gantry doesn't have cameras on it.**

I suspect a lot of it would come down to how that gantry is used. Certainly switching it from blank straight to 40 would cause problems as people close to it panic and slam on while still on what is quite a sharp bend for motorway standards. Providing they ramp it down 60, 50, 40 it should be fine.

Thanks,

**Which I only found out after freaking out, because as you know you can't tell as you approach.

B00st

Wig wrote:

Looking at the google map the bend is a left hand bend before the gantry in question, you have about 200m to see the gantry after rounding the bend, takes 3 seconds to do 100m at 70mph. 6 seconds to do the 200m assuming you see the gantry straight away, and assuming other factors like coming down the hill on approach does not further reduce your ability to see the LEDs lit up. You are looking in your mirror observing all the street furniture around you which complicates everything. Something else might have your attention within the car for a second.or 2. You might be overtaking other vehicles (like I was).
I don't think a 200metre warning (assuming it is visible at 200m) is long enough when you are travelling 70mph.
And remember after travelling through 6 - 7 - 10? gantries already showing no speed limit so you are lulled into believing the system is switched off at the moment.
They give you a half mile warning for the exit and 200m warning for a reduction in speed limit which if you fail to observe is a speeding ticket. And the bridge tols give you a 3/4 mile (36second) warning.

The bend is underneath Rembrandt Way, the gantry is at the sliproad exit for J25.

Under normal current conditions the 4 gantries immediately before the tunnel are permanently on 50 at the moment. The one you are describing is the 2nd that you go through, so you had already missed one of the 50 limits. These two gantries are both visible together before you even have to contemplate slowing down, it doesn't just appear in sight at the last moment requiring panic braking to slow down.

The only one with an 'issue' is by 25A where the signs fade out as you get close to them.

Kite2010 wrote:

Most likely previously in the day there was heavy traffic and somebody forgot to turn it off.

Variable speed limits are fully automatic based on measurements of the prevailing vehicle speeds. They cannot be 'left on' from the previous night. This case things are slightly different as the Westbound tunnel is permanently at 50 for the moment.

Wig wrote:

It is dangerous IMO to change the limit without any prior warning that "the limit ahead is reducing" on a motorway where people are doing 70. and yes some may be half asleep, all the more reason for a prior warning. But I was not overly tired, as I already stated.

How do you propose that they warn that a variable speed limit up ahead is different from what you are expecting? Should the gantry have two limits displayed, one for the current speed limit and one for the next? Though that would be rather confusing. The stretch approaching the tunnels is currently constant, however, on something like the M42 the limit can change between each subsequent gantry. The fact that you are in a Variable Speed Limit zone should be warning enough.

adamc260 wrote:

Someone mentioned a 'grace period' but how long is it? Try telling that to a ticket =/

During the 'grace period' the camera is inactive at the new lower limit so you won't receive a ticket if you go under the gantry above the displayed speed.

Wig

B00st wrote: »

Under normal current conditions the 4 gantries immediately before the tunnel are permanently on 50 at the moment. The one you are describing is the 2nd that you go through, so you had already missed one of the 50 limits. These two gantries are both visible together before you even have to contemplate slowing down, it doesn't just appear in sight at the last moment requiring panic braking to slow down.

Well actually you are dead wrong, I know what I saw, I went through all the gantries switched off, the 2nd one from the tunnel was the first to be switched on. I was doing 70 mph, if what you say was true (and on this occasion it wasn't) Then if either 3rd or 4th before tunnel have cameras on them then I would have had a speeding ticket. Lets be absolutely clear about one thing .....you are wrong.

The only one with an 'issue' is by 25A where the signs fade out as you get close to them.

I also saw this one extremely faded the first before the tunnel.

Variable speed limits are fully automatic based on measurements of the prevailing vehicle speeds. They cannot be 'left on' from the previous night. This case things are slightly different as the Westbound tunnel is permanently at 50 for the moment.

And it's dangerous for unsuspecting drivers lulled into security that they must all be off because the previous 10 have all been off. To suddenly come across one thats on when you are covering 100m every 3 seconds.

How do you propose that they warn that a variable speed limit up ahead is different from what you are expecting?

Simple, have a message saying for 1 or 2 gantries prior "reduced speed limit ahead" then you will be forewarned and everyone is safe.

During the 'grace period' the camera is inactive at the new lower limit so you won't receive a ticket if you go under the gantry above the displayed speed.

How does the average driver know there is a grace period? How long is the period? This would only apply to those who actually see it come on, those arriving 20 seconds later will have no idea they just came on.

B00st

Wig wrote: »

Well actually you are dead wrong, I know what I saw, I went through all the gantries switched off, the 2nd one from the tunnel was the first to be switched on. I was doing 70 mph, if what you say was true (and on this occasion it wasn't) Then if either 3rd or 4th before tunnel have cameras on them then I would have had a speeding ticket. Lets be absolutely clear about one thing .....you are wrong.

I also saw this one extremely faded the first before the tunnel.

There is a gantry immediately before entering the tunnels, the 25A gantry (which fades as you get close) is the 2nd from the tunnel. The gantry before 25 is the 3rd from the tunnel. Regardless of whether the next one out is on or not, the gantry at 25 is visible before you even pass through the gantry before it. So there is plenty of warning and visibility.

Wig wrote: »

And it's dangerous for unsuspecting drivers lulled into security that they must all be off because the previous 10 have all been off. To suddenly come across one thats on when you are covering 100m every 3 seconds.

Why are drivers lulled into a false sense of security? If the sign is off the national speed limit applies, if it is on, then the signed limit is in force. The fact that you are in a variable speed limit zone should mean that you need to be aware that the limit can change at a moments notice. As above, the gantry in question has good visibility to it and can be seen before you pass under the one before it.

Wig wrote: »

Simple, have a message saying for 1 or 2 gantries prior "reduced speed limit ahead" then you will be forewarned and everyone is safe.

The limits on the M42 are far more variable than those on the M4 Newport section, frequently changing between 60,50 or 40 from gantry to gantry, and no one seems to have a problem with the changes. You see the next gantry and change speed to suit.

Wig wrote: »

How does the average driver know there is a grace period? How long is the period? This would only apply to those who actually see it come on, those arriving 20 seconds later will have no idea they just came on.

How does any driver know about the changes to rules and regulations applying to the road? The requirement is on the driver to make sure that they are aware and up to date with regulations and not just assume that nothing has changed since they took the test.

With the changing limit its pretty simple. If you see the sign change (and it is obvious that it is happening as you do get a flash) just as you go under it, don't worry. If the limit doesn't change as you approach assume that the limit is active. On the M42 it is pretty easy just to change speed directly using the cruise control, no need to panic brake because the next gantry has a lower speed shown.

Lum

B00st wrote: »

The limits on the M42 are far more variable than those on the M4 Newport section, frequently changing between 60,50 or 40 from gantry to gantry, and no one seems to have a problem with the changes. You see the next gantry and change speed to suit.

To be fair, the M42 is a lot straighter and has a lot better visibility.

piggeh

How is it different to any other change in speed limit? ie going from a road at 70mph that then reduces to 50mph, you only have permanent fixed road signs pretty much at the point you should reduce to 50. Certainly at night they're not even illuminated, you're lucky to get illuminated ones on the M4.

My only speeding fine was doing 58mph about 20 yards into a 50 zone coming from a 70mph section, so I agree with you a bit of leeway on how quickly they expect you to slow down seems reasonable in some cases. It's just the M4 isn't an exclusive case and is probably a lot more visible than others.

Wig

B00st wrote: »

There is a gantry immediately before entering the tunnels, the 25A gantry (which fades as you get close) is the 2nd from the tunnel. The gantry before 25 is the 3rd from the tunnel. Regardless of whether the next one out is on or not, the gantry at 25 is visible before you even pass through the gantry before it. So there is plenty of warning and visibility.

I agree that there are 2 gantries at 25A one directly on the slip road & another 50m after. I hadn't realised there are 2 so close together at the tunnel....I don't know if they are both used to display the speed limit, I can only see them from above on the satellite view. There is 1 gantry at J25 and it is directly across the slip road, it is this gantry that caught me out, there is a left hand bend some 200 yds before it and you cannot see it from the previous gantry the 4th from the tunnel which in this case was switched off. The highlighted bold words in your quote are wrong, you can see for yourself on google satellite view.

Why are drivers lulled into a false sense of security? If the sign is off the national speed limit applies, if it is on, then the signed limit is in force. The fact that you are in a variable speed limit zone should mean that you need to be aware that the limit can change at a moments notice.

Lulled because they are all switched off for the previous 10 or so, so you assume as the road is empty they are all off. It is the fact that the speed changes at a moments notice that makes the situation so dangerous, there should be prior warning on the previous gantry. It wouldn't be so bad if there were not hidden cameras on them so you know you have to either brake hard or get a ticket.

As above, the gantry in question has good visibility to it and can be seen before you pass under the one before it.

No you can't. You possibly see it after rounding the bend, but with all the street furniture
and the place all lit up with streetlamps it's possibly easy to miss until much closer - not having been back for a second look I can't really comment on why I missed it.

The limits on the M42 are far more variable than those on the M4 Newport section, frequently changing between 60,50 or 40 from gantry to gantry, and no one seems to have a problem with the changes. You see the next gantry and change speed to suit.

As long as there is a clear line of sight between the gantries and the distance of warning is sufficiently long, I would hope that it is ok on the 42, however on the M4 with all the bends and hills up and down I wouldn't say it is safe.

How does any driver know about the changes to rules and regulations applying to the road? The requirement is on the driver to make sure that they are aware and up to date with regulations and not just assume that nothing has changed since they took the test.

Where does it say in the highway code about grace periods? I notice you didn't say how long the period was. Where in the driving test do you get taught that motorway variable speed gantries have grace periods? Whilst it is an interesting aside, it does not alter the fact that people may (& do) panic if they suddenly notice there is a speed restriction....because they don't want a ticket.

With the changing limit its pretty simple. If you see the sign change (and it is obvious that it is happening as you do get a flash) just as you go under it, don't worry. If the limit doesn't change as you approach assume that the limit is active. On the M42 it is pretty easy just to change speed directly using the cruise control, no need to panic brake because the next gantry has a lower speed shown.

There is every need to panic if you are doing 70mph and fast approaching the next gantry which has only just entered your line of sight and you now see the limit is illuminated as 50, you either slam the brakes on or risk a ticket.....these enforcements and signs are dangerous (on the Newport M4 section).

Wig

piggeh wrote: »

How is it different to any other change in speed limit? ie going from a road at 70mph that then reduces to 50mph, you only have permanent fixed road signs pretty much at the point you should reduce to 50. Certainly at night they're not even illuminated, you're lucky to get illuminated ones on the M4.

On motorways this does not usually happen, You get a 1 mile warning of the next exit then a 1/2 mile warning then 300 yrd warning then on the slip road you slow down. On the dual carriage way near where I live there is a 300yd, 200yd & 100yd warnings of a reduction to 50mph (and possibly one warning before that at 1/2 mile) this is the only sensible way to do it IMHO. This is also the way they do it at the M4 toll booths too - a 3/4 mile warning.

I have asked in a previous post for anyone to mention any motorways in UK which have speed reductions on fixed signs and what warning you get of the reduction, perhaps you can tell us which ones you know of?

My only speeding fine was doing 58mph about 20 yards into a 50 zone coming from a 70mph section, so I agree with you a bit of leeway on how quickly they expect you to slow down seems reasonable in some cases. It's just the M4 isn't an exclusive case and is probably a lot more visible than others.

You may be surprised.