London traffic

Sometime between fifteen and twenty years of age, I read something that indicated that the average traffic speed in London had not changed in centuries. That as soon as some type of traffic flow enhancement was implemented, then the volume of users increased, bringing the average speed back down to the longterm average.

I later discovered that this was known as Smeed's Law.

At the opposite end of this theory was Smeed's observations of heavily congested networks. He noted that at some minimum speed, motorists would simply choose not to drive. If speeds fell below 9 mph (14.5 kph), then drivers would keep away; as speeds rose above this limit, it would draw more drivers out until the roads became congested again.

I recently saw this tweet referencing Smeed's Law.

Smeed On!
Avg. speed projected for #London traffic by R.J. Smeed in 1949: 9 mph
Avg. speed of London traffic today: 8.98 mph pic.twitter.com/Wn8U0pZyNn

— Taras Grescoe (@grescoe) November 25, 2016