From a previous post:
by The real Biffo » Sat Dec 19, 2009 1:13 am
The VMS that say “don’t drink & drive” “check your fuel” “don’t hog the middle lane” etc are Campaign messages, people in high places decide which area of the network these signs are going to be displayed, and when, often the data of previous months/years for incidents relating to certain problems is used. ie. the “check your fuel” VMS (Variable Message Sign) were set in know area’s of high proportions of breakdowns due to drivers running out of fuel. These messages are set by the NTIS.
The VMS that say, “10 miles to J21A, 10 mins” etc, are set automatically by ANPR readers, these note the last 3 digets of numberplates, and check how long it takes for them to get to the next checkpoint (never giving a time less then 70mph would take!)
The VMS that say anything to do with “Queues” are set automatically by MIDAS (go look it up!) these are basically loops in the road surface that measure the average speed of traffic flowing over them, slow abnormal loads will trigger these as well. A certain amount of traffic has to flow over the loops faster than the trigger speed to clear the settings. The system automatically scans the loops every 4 minutes or so.
Any message that tells of congestion or a road closure miles away, is set by the NTIS (National Traffic Information Service ) this is based in the midlands, and sets the messages according to how long the incident is reported as possibly lasting)
Any VMS that says anything to do with accident, debris, obstruction, lane closures etc. we set manually, and is in the location reported, this however can be wrong if the informant is unsure where they actually are. Unfortunately this does happen all too frequently! also often the location is given "between Junction # and junction #, so the signals have to be set for 50’s between those junctions, until either confirmed and adjusted, or “Not traced”.
You may also see the signals set but not see anything if it’s just been removed, and the patrol has not radio’d for the signals to be cleared, (this also takes a couple of minutes) if you see speeds of 50, then usually it’s not been confirmed by either CCTV, a police patrol, or HATO patrol finding it yet, once it’s confirmed as being there, the signs should be changed to whatever best matches the problem, or cleared if “no traced”
So if you see signs for lane closures, move out of the affected lane straight away,(remember, if you go through a red X, you can be booked!) keep the traffic flowing, don’t run up to the cones then make the other lane stop to let you in. Lane closures are not put on for the fun of it, trust me!
If an incident is reported, we have to set signals, these can only be authorised to be cleared by a patrol (police or HATO) that is at scene, or has checked through the scene.
The manual signal settings are “Quality checked” on a ramdom basis, with every operator having their setting checked regularly. anyone who falls below the required standard is given extra tuition etc. These requirements mean the signals have to be set correctly to the information received, within the time limit from the start of the log. and cleared within the time limit after being informed to do so.
Now and again, the system can have problems (as all computers do!) and until the engineer resets it, we can’t clear or set signals, thankfully this doesn’t happen often.
Then there’s ROADWORKS, usually set during the night-time, but …don’t get me going about roadworks!!!
all because the signs on the m1 bout j24 to j22 were warning of ques at j22 … they was none!! they was a long load but no ques, inbetween they were warning m1 was closed j20-j19 but after you passed j21 the next sign informed us of 1hour 30min delays between j21 and j20 
