PowerSwitch

On most urban roads.
Good news in my view. Less noise and pollution.
Roads safer for walkers, cyclists and horses.
https://www.bbc.co.uk/news/uk-wales-62020427

Great if all vehicles were electric, which are most efficient at very low speeds, but petrol and diesel will be far less efficient running around in low gears and high revs, and if my local area is anything to go by the few vehicles that stick to 20 will become targets for abuse by the 40mph brigade, and police enforcement will be conspicuous by its absence.

I had a look at my cars revs and speed this morning, 20mph is 1200 rpm in third gear, quite a comfortable revs for that engine / car combination. In fourth gear it's 900 rpm which is too low. The car has six forward gears. I intended to find a quiet stretch of road, reset the computer and find the mpg at 20 mph, but couldn't find an empty road.

I'm guessing that the increased engine frictional and pumping losses of driving in third gear instead of fifth or sixth will at least equal the gains from less wind resistance.

Presumably there will also be less ware on brakes and tyres. I think these days, brake and tyres are responsible for a significant proportion of urban particulate pollution.

I would have thought there is some kind of magic combination of torque and speed for an engine where it approaches maximum efficiency and then there is the increasing effect of air resistance which is speed to the power four that gives you the sweet spot.

I drove a hybrid rental car and the mileage was better in urban driving than open road driving so the lower speeds must be more efficient when you get your 'money' back on the regenerative braking. I get better mileage around 50mph/80kph with a normal IC engine car.

Electric Car



IC Cars

The new Welsh speed limit limit of 20 MPH has come into force. It applies to most but not all roads previously subject to a 30 limit.
20 MPH is the default limit on all roads in built up areas, unless a higher permitted speed is advertised.
This prevents drivers exceeding the 20 limit if the signs have been removed, defaced or vandalised.