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M4 Junctions 19+20 Speed Enforcement


The section of the M4 between junction 19 & 20 has a variable speed limit with enforcement cameras. These cameras are now active outside of the operating hours of the variable speed limit, enforcing the national speed limit.

1. What is the purpose of these enforcement cameras?

2. How many overhead gantries in each direction have enforcement cameras and what are their locations?

3. What date did these cameras become active in enforcing the national speed limit?

4. What speed will trigger the enforcement camera and trigger a NIP to be sent to the vehicle's registered keeper?

5. Since the cameras have been used to enforce the national speed limit, how many NIP have been issued?

a. What speeds were the vehicles travelling which received a NIP.

6. Where is the revenue raised from these alleged speeding offences spent?

7. What is the average speed limit for the M4 motorway (within A&S) for the hours outside of the variable speed limit?


1. The purpose of the cameras is to enforce the managed motorway in the same way that any other speed limit is enforced.

2. There are 36 cameras on overhead gantries. I am not obliged to provide locations of the enforcement cameras it has been deemed exempt from disclose by virtue of Section 38 of the Freedom of Information Act relating to health and safety considerations.

Section 38 is a qualified, prejudice based exemption and therefore there is a requirement to evidence the harm that would be caused by disclosure and to conduct a public interest test. Please see this below:

Harm in disclosure

Releasing the locations of the cameras on the overhead gantries would have a negative impact on road safety. Drivers could dramatically reduce their speed when they are aware there is a camera in order to avoid detection. This would or is likely to cause collisions.

Arguments favouring disclosure

Release of the locations of the cameras would demonstrate openness and transparency and would add accuracy and credibility to public debate on this area of policing.

Arguments against disclosure

A smart motorway uses technology to actively manage the flow of traffic. The technology is controlled from a regional traffic control centre. The control centres monitor traffic carefully and can activate and change signs and speed limits. This helps keep the traffic flowing freely.

Smart motorways increase the capacity of the road, without the expense and hassle of widening the road, by either temporarily or permanently opening the hard shoulder to traffic.

Highways England is responsible for smart motorways in England.

The objective of the smart motorway is to manage the flow of traffic. To disclose the specific locations of the cameras on this stretch of motorway would contradict these efforts and adversely affect road safety as disclosure would enable the less diligent drivers to increase speed and brake in locations where they are aware a camera is present. 

Avon and Somerset constabulary is charged with enforcing the law and protecting the public. Information will not be released if it would, or would be likely to endanger the physical or mental health, or the safety of any individual.

Balance test

Having weighed up the arguments both for and against disclosure, it has been decided that the balance test is weighted in the favour of non-disclosure. Although there is public interest in openness and transparency, the constabulary will not disclose any information that has the potential to endanger the health and safety of any individual.

3. The first date of enforcement was 11th April 2014.

4. The thresholds for the cameras are all set at or above the ACPO guidelines of 10% of the speed limit plus 2mph. The speed limit is displayed on the gantry, or if the gantry signs are not active, then the national speed limit applies.

5. A total of 26,837 notices of intended prosecution (NIPs) were issued.

5a. NIPs were issued to drivers speeding at 81mph through to 148mph, with the following exceptions; no NIPs were issued for 140mph, 141mph and 146mph.

6. The Fixed penalty and fines awarded by the courts go to the Treasury, for anyone who attends an educational course the Road safety Support Unit receives £35 of the penalty and this is ring fenced to pay for Road Safety and the entire Speed Enforcement Unit.

7. The national speed limit applies.

FOI reference 881/16.

Date of request: 04.07.16