(Image: NQ)
DRIVERS on smart motorways have to be ready for the speed limit signs to change - but how quickly after a change are overhead speed cameras activated?
Motorists on the M62 between Leeds and Bradford have become used to overhead signs display lowered speed limits.
Ignoring the signs can lead to prosecution for speeding, a fine and penalty points.
But drivers have asked how quickly do speed cameras adjust to lower limits after a change.
One driver said: "Last week I was driving on the M62 minding my own business at 70mph when the overhead signs changed to 50mph a split second before I passed them.
"I didn't see a flash - but how soon will the speed cameras become active after a change? I'm worried."
According to traffic authorities, drivers should be given a reasonable amount of time to slow down.
Police ensure there is a minimum time delay between a variable speed limit changing on a gantry and enforcement beginning. This is usually around one minute.
However, the guidance does not state how long that delay is.
The delay is intended to give drivers time to slow down safely and sensibly. Motorists should therefore obey any speed shown inside a red circle, as it is legally enforceable.
Variable speed limits are shown on illuminated electronic signs at the side of the motorway or on gantries above the lanes. They can be used to manage traffic flow, improve journey time reliability and reduce the risk of collisions.
Research by the Government and the road industry has found that excessive speed is common on motorways. Analysis of traffic incidents has also confirmed a link between vehicle speeds, the likelihood of collisions and the seriousness of injuries.
A speed limit may be reduced because of congestion, roadworks, traffic officers working in vulnerable locations, extreme weather or an incident. Drivers may not always be able to see the reason for the change.
The reason does not affect whether the limit can be enforced. A speed limit shown inside a red circle remains enforceable by police, and the reason for lowering it does not need to be provided.
When a new limit or a closed lane signal is detected, the relevant enforcement equipment carries out a self-check. Vehicles passing at that point may see a flash.
A flash does not necessarily mean a vehicle has been recorded exceeding the displayed limit. The self-check can take place when the sign or lane signal changes.
Questions about enforcement should be directed to the relevant regional police force. Guidance does not provide a single national period, in seconds or minutes, between a change appearing and a camera becoming active.
Drivers must also continue following the previous instruction if a sign becomes blank or unlit. A blank sign does not cancel a lower limit shown on an earlier gantry.
When a lower limit ends, the national speed limit symbol is used to tell drivers that the restriction has finished. Until that symbol is passed, the lower speed limit continues to apply.
A technical fault may prevent the national speed limit symbol from appearing. If that happens, the signal-setting system should move the symbol to the next available display.
Motorists should continue to follow the lower limit until they pass the national speed limit symbol. This applies even if a later gantry is blank.
There are separate arrangements around roadworks. Drivers may first see a lower limit on an electronic gantry before reaching a series of blank gantries through the works.
In those areas, a 50mph limit and its ending are normally shown on temporary metal signs at the roadside. The national speed limit is restored where the appropriate sign is displayed.
In exceptional cases, electronic variable limits may appear within a roadworks area where temporary signs already set the limit. Anyone unsure which instruction applies is advised to follow the lower speed shown.
Enforcement will not take place if a service-affecting fault affects the speed camera or the related variable speed limit display. Whether police issue a Notice of Intended Prosecution depends on the related technical equipment working as intended.
Drivers should not rely on a blank sign, a flash or uncertainty about the enforcement delay. They must follow the latest clear instruction shown inside a red circle, slow down safely when a limit changes and continue obeying it until the national speed limit symbol is passed.
The system is designed to manage traffic and support road safety, but responsibility remains with motorists to observe displayed limits. No published figure in the guidance confirms the exact number of seconds before a camera can enforce a changed speed.