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

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 UKPolice forceNumber of camerasCamera activation thresholdAvon and Somerset4110% + 2mphBedfordshire38Would not reveal thresholdCambridgeshire32Would not reveal thresholdCheshire1510% + 2mphCleveland410% + 2mphDerbyshire1810% + 2mphDevon and Cornwall9810% + 2mphDurham0 fixed10% + 2mphEssex63Don’t use a standard thresholdGreater Manchester235Would not reveal thresholdGwent2110% + 2mphHampshire3610% + 2mphHertfordshire53Would not reveal thresholdKent10910% + 2mphLancashire3410% + 3mphLeicestershire3010% + 2mphMerseyside1810% + 2mphMetropolitan Police/TfL80510% + 3mphNorfolk2610% + 2mphNorth Wales2810% + 2mphNorthumbria5510% + 2mphNottinghamshire48Refused to confirm if threshold existsPolice Service of Northern Ireland1210% + 2mphScotland173Refused to confirm if threshold existsSouth Wales13710% + 2mphSouth Yorkshire2510% + 2mphStaffordshire286Would not reveal thresholdSuffolk410% + 2mphThames Valley29410% + 2mphWarwickshire2810% + 2mphWest Mercia2310% + 2mphWest Midlands33Would not reveal thresholdWest Yorkshire40210% + 2mphCan 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.

ModelTrue speed at indicated 30mphTrue speed at indicated 50mphTrue speed at indicated 60mphTrue speed at indicated 70mphKia e-Niro First Edition27mph47mph57mph67mphBMW i3s28mph48mph58mph68mphSEAT Arona 1.0 TSI 11529mph49mph60mph69mphSEAT Tarraco 2.0 TDI 150 manual29mph49mph59mph68mphSkoda Kodiaq 2.0 TDI 150 manual28mph48mph57mph67mphPeugeot 5008 BlueHDi 130 manual28mph48mph57mph68mphVolvo XC40 D4 auto R-Design30mph49mph59mph69mphMazda MX-5 2.027mph48mph58mph68mphDacia Duster dCi 11528mph48mph58mph68mphBMW 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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