Here you will often see a sigh with a posted speed to maintain a green wave down the road, it is the most sensible thing to do as all those stop/start maneuvers are hard on the environment.
We even have green wave for Cyclists on the bicycle paths.
Such a sign could look like this.
It say green wave, every day from 12:00 to 18:00 if you maintain a speed of 20 km/h
The green wave are of course not something you can just drop down on a stretch of road, often you will just find it only work in one direction for a road.
My birth town of Aarhus are not really geared for car traffic in the center, just like London, so for a long time they have talked about banning cars there for anyone that do not live there, and then instead of having the parking garages downtown they will be put outside the city center and people then have to take the bus or light rail to the center.
I think the idea are fine, the layout of the old city planners did not foresee current day traffic, so it is a part of the path of mankind as we have evolved.
Now Aarhus are of course a whole lot smaller than London, but the problems are the same, but the people living in London and the people Managing London just have bigger challenges.
Aarhus you can easy walk all over the town center in 1 hour 2 or 3 hours if you want to walk across the whole town, its just 6 - 7 Km from the signs south of town to the signs saying you leave town in the north, and pretty much the same in a easy / west direction.
London have a head start with the tube, Aarhus just now getting light rail / trams again after trams was phased out in the early 70ties.