What are those little grey boxes on the M25?

Vic · Posted: Sat Jan 29, 2005 4:29 pm Post subject:

The short devices with three lenses at the front are indeed forward scatter visibility sensors. Commonly known as fog detectors.

cebab · Occasional Visitor Joined: Jan 13, 2005 Posts: 2

I am pretty sure that they are fog detectors

These occur on most urban motorways in the UK. They certainly are on the M4

Try to get a fix on one and post the position here and I will try to take a look next time I am passing.

Most frequent is M11 to Watford and A22 to A3

Andrew

Laze · Occasional Visitor Joined: Dec 02, 2003 Posts: 8

I remember reading that only one of the 4 cameras on a gantry can be active at a time due to potential radar interference between the cameras. (Someone took this to court and escaped prosecution on this technicality)
From my personal observations I think the cameras are only active when the matrix boards are displaying a reduced speed limit. I would certainly not bet my license on this theory though !

The cameras in the road works are evil - I often see them flash people only doing slightly > 40 so be very carefull if driving that section at night. (You are lucky to reach 40 during the day !)

Stephen

Darren · Posted: Wed Feb 02, 2005 4:06 pm Post subject:

The variable speed limit cameras on the M25 are indeed only active when a variable speed limit is in force.
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Darren Griffin

MrMcC · Occasional Visitor Joined: Feb 02, 2005 Posts: 1

I drove under those Gatso gantrys on the Surrey Stretch of the M25 with a Cobra laser detector connected to my car about a year ago.

I drove from The M4 round to the gatwick M23 junction and about 3 bridges were live.

I`m sure someone else will be able to comfirm that too??

Darren · Posted: Wed Feb 02, 2005 10:03 pm Post subject:

There are a lot more than that with active cameras, from memory there are at least 20 -25 gantries with Gatso installations, all now digital as well. The variable speed limit runs from just North of the M4 Intersection to the A3 Intersection att Junction 10,

All are active and as I said earlier are only 'live' when the variable limit is in force.
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Darren Griffin

swing · Posted: Thu Feb 03, 2005 11:23 am Post subject:

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