A lot of blocks of the misunderstood kind being put out here. In a time where roads have become mass transit systems and no longer “the open road” of a time when there was much less traffic, travelling slower in general is already built in, like it or not…

Getting to 30mph or more, is often just stupid but it’s what folk were taught to do in training… When experiencing difficulty and learning from it, wasn’t going to happen if all the traffic ahead disappeared into the distance.

If you’re qualified you should be doing it better. Maybe driving slower if going faster would be as wasteful or as pointless as tailgating in a three lane wide, traffic jam.

There’s an issue not mentioned… Braking. (To a lesser degree, simple deceleration in low gears from high speeds too), turns fuel already burned and used, back into heat. Which is wasted fuel. The less fuel burned to get to a common speed, without frequent or hard braking means greater distances travelled with a closed or almost closed throttle, with an air increase, metered by computer.

If average speeds in an area are low due to congestion and normal conflicts with other road users etc, then fuel used to get to, let’s say, 4 times possible average speed, is three lots of fuel wasted.

And arguing low gears wastes fuel, is pretty silly. Few if anyone has a fixed fuel jet carburettor with an enrichment jet anymore… Fuel injectors and computers are more than capable of metering low fuel at a steady throttle level at a low speed even if revs are 15% or so, higher.

My old semi auto, (it has a clutch-less robot manual type gearbox), knows if I’m going up or down a hill and if (by throttle pressure), I want more fuel or none at all… It usually gives me the right gear too and even seems to know it I have one or five people in the car as well…
It must do because on identical unhindered journeys within a few seconds timing of each other, the fuel consumption increases with extra folk on board but I’ve done nothing in particular, in automatic, to cause that increase.