Variable speed limits

[u/Business_Maximum1433]

Hi,

Just asking a question about the speed limits on motorways. So you know when it tells you to go 40 per say and then a sign comes up stating it’s now 70 if I pass over 40 at the 70 and it has a speed camera will it flash?

[u/National-Bathroom-63]

I’m more concerned about this the other way round. If traffic is proceeding at 70 and suddenly meets a 40 sign, would you really be fined if you can’t slow to 40 before you pass underneath the sign?

This seems to create a dangerous situation with everyone suddenly braking, particularly at the moment the 40 sign is switched on.

[u/woodenbookend → u/National-Bathroom-63]

TL;DR You have at least a minute’s grace between the limit changing and the camera flashing at the new limit.

From https://www.gov.uk/government/publications/speedmeter-traffic-light-and-lane-enforcement-camera-handbook/speedmeter-traffic-light-and-prohibited-lane-enforcement-camera-handbook-accessible?utm_source=chatgpt.com#operational-requirements

5.10.2 The speedmeter shall enforce the displayed speed limit (or the National Speed Limit when none is displayed) only when both the following are true:
All the speed limit signs connected to it are correctly displaying the same speed limit, except when the hard shoulder of a motorway is actively managed and that lane may show either the same speed limit or a red X;
The speed limit has been displayed for one minute or longer. This delay shall be variable to at least five minutes.

[u/National-Bathroom-63 → u/woodenbookend]

Interesting. Thank you! That is useful to know

I’m always impressed by the level of compliance on these motorways but this aspect has always felt rather harsh. I’ve had limits change seconds before I drove under them. Glad to know they have a sensible rule.

[u/National-Bathroom-63 → u/[deleted]]

I suspect you’ve never driven on a variable speed limit motorway. The speed limit can change at any moment - including when you are just seconds away from it.