Revealed: the margin for error for UK speed cameras

Speed cameras UK

It’s a burning question for UK motorists, be they speed-obsessed or strait-laced: what can you ‘get away with’ when it comes to speed cameras? Obviously, prescribed speed limits are there for a reason, and you should adhere to them to the best of your ability. But what is the margin of error, allowing for small excesses of speed? We look at the facts.

So what are the tolerances? It’s useful to know whether cameras will nick you on a decimal point, or whether there’s some leeway. Here’s the latest on the issue…

Recently, rumours have spread that there is little room for error when it comes to speed cameras. If it’s a 30 and you’re doing 31 mph, they say, prepare for an unwelcome letter in the post. 

It is unclear how such speculation has arisen. That it may have caused drivers to watch their speed more closely is a welcome side-effect. The truth, however, is a little different.

Speed camera tolerances: the truthSpeedcurb camera on Millbank in Westminster

Auto Express did some digging on the issue last year, including procuring figures from many of the UK’s police forces via freedom-of-information requests.

Consider the rumours about cameras with 1 mph tolerances, debunked.

Nearly all the forces that responded gave a 10 percent plus 2 mph threshold. That applies for both normal ‘Gatso’ style cameras, and any others that clock an individual speed case, as well as average speed check zones with multiple cameras over a distance.

Doing the maths, that means “safe” speeds could be as high as:

  • 79 mph in a 70 limit
  • 68 mph in a 60 limit
  • 57 mph in a 50 limit
  • 46 mph in a 40 limit
  • 35 mph in a 30 limit

Note the quote marks, though. Limits are limits for good reason that we shouldn’t need to explain at length – and a threshold doesn’t necessarily need always to be followed…

Curiously, two forces reported a 10 percent plus 3 mph threshold – Lancashire and the London Metropolitan Police. Add another mph to each of the above numbers.

According to Auto Express, the reasons given for this higher tolerance are to do with higher traffic numbers in London. In the case of Lancashire, it’s to give just that little bit more wiggle room.

Why is there such a wide margin for error in speed cameras?

Speed cameras UK

Error is just the word. Different cars show speeds to varying levels of accuracy. Some will show you’re doing 60 mph, when you’re actually going 57 mph. Construction and use regulations specify your speedo can over-read by 10 percent, but under-read by zero percent

The threshold is there so that drivers have no excuse if they’re caught. If you’re flashed, it’s more likely that you’re deliberately breaking the limit if you’re travelling at 80 mph, as opposed to 72 or 73. It serves both the interests of fairness and indeed, reduces workload for the justice system.

Every offence takes paperwork, they don’t just get your money for free, and that’s without factoring in offenders potentially appealing charges.

Wiggle room, therefore, serves both motorists and the authorities well.

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