M4 Near Reading

[mphJ]

I was just curious about the smart motorway gantry cameras and how they work

Do they flash you when you re coming towards it ? I thought if you re going to get flashed its from behind after you go under it ?

So I was on the M4 near reading on the stretch heading towards London

Nothing illiuminated on the screens on the gantry so obviously 70mph and I was doing 73mph max

Around 4 cars in front I see a flash and then when I get to it just before I see another flash

So fair enough if they re going to get me for doing 73mph although I heard speedos read a bit high anyway ? 2015 BMW

Anyway I was just curious does anyone know this stretch of the M4 and had any experiences with it ? And do those gantry camera flash you as you come towards it ?

I can t really picture where the flash come from so may have been on the opposite side I don t know , I was in the outside lane , but like I said there were quite a few cars around me all doing similar speed so was doing 73 max so seems a bit harsh if I ve been done for that but if I get it I get i suppose

many thanks

Edited by mphJ on Sunday 1st February 08:18

[E-bmw]

For 73 in a 70 you would not hear any more.

The flash is to take a picture of the rear of the car and the gantry behind you to show the speed limit in force at the time done with 2 separate cameras linked in time.

A displayed 73 would likely be 71 real speed at the most.

[mphJ]

Ok thanks for the reply , so you’re saying it’s possible the flash was on the other side getting someone from the rear

Thanks

[MattyD803]

I live just off the M4 in Berkshire and hence use it daily.

I can confirm, any flashes intended for your vehicle, will be from behind you. They emanate from yellow cameras which are attached to the far left hand side of the main gantry.

You likely saw something from the otherwise….and besides….even 76/77mph (on a typical Speedo) doesn’t set them off. I’d hazard a guess at 80mph+, but never tested it naturally.

[John D.]

MattyD803 said:

I live just off the M4 in Berkshire and hence use it daily.

I can confirm, any flashes intended for your vehicle, will be from behind you. They emanate from yellow cameras which are attached to the far left hand side of the main gantry.

You likely saw something from the otherwise .and besides .even 76/77mph (on a typical Speedo) doesn t set them off. I d hazard a guess at 80mph+, but never tested it naturally.

They work at 80 (on the clock of the Megane RS I had at the time) . I foolishly tested this a few years ago.

As you say, they are very easy to spot on the ends of the gantries.

[Terminator X]

Hadex is on the gantry to the left of it usually yellow cameras and a grey "platform". They watch the car as it drives past the gantry so as others say the flash will be as you go past.

Do they flash though? I was under the impression that modern cameras are UV or similar so no flash.

TX.

[John D.]

They definitely flash.

[BertBert]

Terminator X said:

Hadex is on the gantry to the left of it usually yellow cameras and a grey "platform". They watch the car as it drives past the gantry so as others say the flash will be as you go past.

Do they flash though? I was under the impression that modern cameras are UV or similar so no flash.

TX.

Hadecs

[Terminator X]

BertBert said:

Terminator X said:

Hadex is on the gantry to the left of it usually yellow cameras and a grey "platform". They watch the car as it drives past the gantry so as others say the flash will be as you go past.

Do they flash though? I was under the impression that modern cameras are UV or similar so no flash.

TX.

Hadecs

Bless you

TX.

[Ikemi]

The M4 cameras flash, but they flash vehicles from behind. I regularly see them flashing on the other side of the road.

[Cyberprog]

MattyD803 said:

I live just off the M4 in Berkshire and hence use it daily.

I can confirm, any flashes intended for your vehicle, will be from behind you. They emanate from yellow cameras which are attached to the far left hand side of the main gantry.

You likely saw something from the otherwise .and besides .even 76/77mph (on a typical Speedo) doesn t set them off. I d hazard a guess at 80mph+, but never tested it naturally.

I've always run at 75 on the speedo through them, which for my Kia is about 70/71. No issues. I stick religiously to the limit however on two cameras on the M4 between J19 (M32) and J20 (M4/M5 Interchange) and the cameras on the M5 between J16 (A38) and J17 (Cribbs Causeway). They are known to be very tight on tolerance there.

[BertBert]

Cyberprog said:

I've always run at 75 on the speedo through them, which for my Kia is about 70/71. No issues. I stick religiously to the limit however on two cameras on the M4 between J19 (M32) and J20 (M4/M5 Interchange) and the cameras on the M5 between J16 (A38) and J17 (Cribbs Causeway). They are known to be very tight on tolerance there.

I habitually run at 77 on the satnav (where conditions allow). I bet the tolerance you mention is no worse that 10%+1 at those places you mention.

[2020vision]

Cyberprog said:

I've always run at 75 on the speedo through them, which for my Kia is about 70/71. No issues. I stick religiously to the limit however on two cameras on the M4 between J19 (M32) and J20 (M4/M5 Interchange) and the cameras on the M5 between J16 (A38) and J17 (Cribbs Causeway). They are known to be very tight on tolerance there.

The tolerance is the same everywhere

[AddyT.]

The other posts on here are spot on about that section of the M4. Fairly aggressive cameras when there’s lane closures! On a dark Sunday night a couple of years ago they were closing lanes down for overnight roadworks so the signs in the gantry were telling everyone to get in lane one and do not exceed 40. The traffic was near stationary trundling along in lane one. However, woe betide you if you were one of the cars in lane two doing 2mph indicating to join lane one as you were passing under the gantry. Saw multiple cars get flashed! Probably still have the video somewhere.

[Cliftonite]

AddyT. said:

The other posts on here are spot on about that section of the M4. Fairly aggressive cameras when there s lane closures! On a dark Sunday night a couple of years ago they were closing lanes down for overnight roadworks so the signs in the gantry were telling everyone to get in lane one and do not exceed 40. The traffic was near stationary trundling along in lane one. However, woe betide you if you were one of the cars in lane two doing 2mph indicating to join lane one as you were passing under the gantry. Saw multiple cars get flashed! Probably still have the video somewhere.

Those gantries will have been showing a red X?

Passing under one is therefore a well-deserved £100 fine + 3 points on a licence!

[RotorRambler]

Something else in that stretch, as you pass under the gantries you do get hit by some light from above, their illumination, can be a bit off putting !
As in the other posts, always seeing the ones being set off on the opposite carriageway.