Speed limit arithmetic
9 February 2026 03:53 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
igenlode"It took an average of three minutes and 38 seconds to drive one kilometre (0.6 miles) in the centre of London last year... This was partly blamed on widespread 20mph speed limits" -- *what*?
20mph is 32km/h (using the rule-of-thumb conversion ratio of 5:8). So if you were travelling at 32 kilometres per hour it would take (60/32)=1.875 minutes to cover one kilometre: 1 minute 52 seconds. Clearly the majority of the time spent driving in central London is already spent travelling at speeds far *lower* than 20mph; probably spent stationary in traffic jams consisting of other cars. So just how fast are they expecting drivers to sprint between traffic jams in order that increasing the maximum speed limit will reduce journey times?
20mph is 32km/h (using the rule-of-thumb conversion ratio of 5:8). So if you were travelling at 32 kilometres per hour it would take (60/32)=1.875 minutes to cover one kilometre: 1 minute 52 seconds. Clearly the majority of the time spent driving in central London is already spent travelling at speeds far *lower* than 20mph; probably spent stationary in traffic jams consisting of other cars. So just how fast are they expecting drivers to sprint between traffic jams in order that increasing the maximum speed limit will reduce journey times?