While this is a point the naysayers brought up, the slower speeds during the trial period reduced accidents, the severity of accidents, and the slower speeds encouraged more foot and bicycle traffic on those roads

if the cars are designed to use the same fuel for less useful output power, then they’re very badly designed.
i’m sure they might be less efficient in terms of miles per gallon. but they surely can’t be so bad as to waste absolutely more fuel at lower speeds.

if they are, fuck them.

Most cars, at least in NA, have excessively large engines. It is crazy that we use 2L engines to carry one person around, when their own legs would suffice.

Wouldn’t this, in the end, make cars have to shift to a lower gear, thus keeping about the same RPM, and thus eating about the same amount of fuel

That’s not how cars work, they definitely don’t use the same fuel in different gears at the same RPM. See this Wikipedia article for a discussion of speed vs fuel economy.

And as pointed out by the the FAQ, that’s doesn’t not factor in acceleration:

Will driving at 20mph mean I use more fuel?

No. Fuel consumption is mainly influenced by the way we drive – driving at a consistent speed is better than stopping and starting. Accelerating up to 30mph can take twice as much energy as speeding up to 20mph.

A default 20 mph limit and a smooth driving style, can help avoid unnecessary speeding up and slowing down, saving fuel.

afaik most of the sound comes from the tires, not necessarily the engine or the exhaust. obviously not the case for every car, but for most commuter cars it is. the faster the tires are rolling, the louder the sound.

A lot of cars can cruise at 20-25mph just idling in Drive, foot completely off both gas and brake. The RPMs don’t get much lower than that.