UK speed camera tolerances revealed: is your car's speedo accurate?

We investigate the internet rumors surrounding UK speed camera tolerances and whether your car speedo can be trusted

Speed camera

At the start of 2019, rumours swept the internet that speed camera tolerances on certain motorways were so strict, they would issue tickets if drivers exceeded the 70mph limit by just 1mph.

Those stories turned out to be untrue and unfounded. But rather than allow misinformation about speed camera ‘thresholds’ to circulate unchecked, Auto Express asked the UK’s 45 police forces via Freedom of Information requests how strictly their 3,224 speed cameras enforce limits.

UK speed cameras explained

The majority of the forces that responded said their cameras would only activate when drivers exceed the speed limit by 10 per cent plus 2mph, in line with prosecution guidelines from the Association of Chief Police Officers. 

This means cameras won’t issue tickets until someone is driving at 35mph or more in a 30mph limit, or 79mph or more on the motorway, for example. 

The Metropolitan Police, which uses a less strict, 10 per cent plus 3mph threshold, say this is “a proportional response to the high volumes of traffic” in the capital. Lancashire Police also sets its cameras so that they activate at 10 per cent plus 3mph, and says that this has been done “to ensure greater tolerance or discretion”.

A number of forces wouldn’t tell us their camera thresholds, arguing that knowledge of these would encourage drivers to speed. All police forces that told us their thresholds said these applied to both fixed and average speed cameras.

Speed camera thresholds across the UK

 

Police force

 

Number of cameras

 

Camera activation threshold

Avon and Somerset4110% + 2mph
Bedfordshire38Would not reveal threshold
Cambridgeshire32Would not reveal threshold
Cheshire1510% + 2mph
Cleveland410% + 2mph
Derbyshire1810% + 2mph
Devon and Cornwall9810% + 2mph
Durham0 fixed10% + 2mph
Essex63Don't use a standard threshold
Greater Manchester235Would not reveal threshold
Gwent2110% + 2mph
Hampshire3610% + 2mph
Hertfordshire53Would not reveal threshold
Kent10910% + 2mph
Lancashire3410% + 3mph
Leicestershire3010% + 2mph
Merseyside1810% + 2mph
Metropolitan Police/TfL80510% + 3mph
Norfolk2610% + 2mph
North Wales2810% + 2mph
Northumbria5510% + 2mph
Nottinghamshire48
Refused to confirm if threshold exists
Police Service of Northern Ireland1210% + 2mph
Scotland173
Refused to confirm if threshold exists
South Wales13710% + 2mph
South Yorkshire2510% + 2mph
Staffordshire286Would not reveal threshold
Suffolk410% + 2mph
Thames Valley29410% + 2mph
Warwickshire2810% + 2mph
West Mercia2310% + 2mph
West Midlands33Would not reveal threshold
West Yorkshire40210% + 2mph

Can you trust your car speedo?

In addition to asking police how strictly their speed cameras enforce limits, we investigated how accurate the speedometers on 10 cars were. We did this by comparing how fast they said we were going with our actual speed, revealed by a VBox meter. 

Car speedometers are not allowed to ‘under-read’ – they can’t tell you you’re going more slowly than you really are – but they are allowed to over-read by up to 10 per cent plus 6.25mph. So they could read 50.25mph at 40mph. 

All the cars we assessed were well within legal limits, although some read with near-perfect accuracy, while others over-read by 3mph. This, with the different approaches police have to enforcing limits, means some variance will always remain around speeding. 

Commenting on our investigation, AA president Edmund King said it is “sensible to have some flexibility” with speed-limit enforcement, “as the last thing we need is drivers concentrating solely on the speedo and not the road”.

King added that, with speedometers becoming increasingly accurate, “Auto Express’s testing is a valid reminder to drivers not to gamble on their speedo perhaps providing some leeway”.

UK speeding fines and how to appeal them

Our speedo accuracy test explained 

The VBox is a clever piece of kit that uses a GPS signal to measure a car’s speed. It’s very accurate, gauging velocity to within 0.1km/h, so is perfect for assessing speedos.

We set our test cars to 30, 50, 60 and 70mph using the built-in speed limiter or cruise control to ensure a steady speed, then used the VBox to measure how fast we were going. This gave us a fair idea of the discrepancy between actual and indicated speed.

“Not many drivers have access to a VBox, but a separate smartphone app or sat-nav can give you an idea of how accurate your speedo is.

 

Model

 

True speed at indicated 30mph

 

True speed at indicated 50mph

 

True speed at indicated 60mph

 

True speed at indicated 70mph

Kia e-Niro First Edition27mph47mph57mph67mph
BMW i3s28mph48mph58mph68mph
SEAT Arona 1.0 TSI 11529mph49mph60mph69mph
SEAT Tarraco 2.0 TDI 150 manual29mph49mph59mph68mph
Skoda Kodiaq 2.0 TDI 150 manual28mph48mph57mph67mph
Peugeot 5008 BlueHDi 130 manual28mph48mph57mph68mph
Volvo XC40 D4 auto R-Design30mph49mph59mph69mph
Mazda MX-5 2.027mph48mph58mph68mph
Dacia Duster dCi 11528mph48mph58mph68mph
BMW 330i M Sport28mph48mph57mph67mph

Do you think that UK speed camera tolerances are too strict? Let us know in the comments below...

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