First was the roundabout. I can't count how many times *after* we returned to the US that I'd be sitting at some stoplight at an intersection late at night with no other vehicles within a mile, waiting & waiting & waiting & waiting for a green light, and thinking fondly of those good old days in England with their wonderful roundabouts.
The other aspect was lane usage on the Motorways (ie Interstates). Everyone was expected to stay in the slow lane AT ALL TIMES, except when in the act of passing. And you were expected to pass quickly and then immediately pull back into the slow lane. This was self enforced by all the other drivers, who would blink their headlights in your rear view mirror, followed by honking if you didn't pull over quickly. "Camping out" in the fast lane made EVERYone annoyed with you; absolutely NOBODY sympathized that you had an underpowered vehicle (a rented motorhome), and had mistakenly tried to pass a large truck just as a long hill was coming up and you found you only had enough power to pull level with the truck. If you found yourself in that situation and faster cars were coming up behind you, then you were expected to immediately slow down and pull back into the slow lane *behind* the vehicle you were trying to pass.
This system only broke down in traffic jams when it was stop & go in both the fast & slow lane. But the vast majority of the time this system worked well and made things move very quickly on an average-traffic day.
I really, really also missed this aspect when we returned to the States. Ie when there's a long line of cows in the slow lane all doing 55mph in a 60mph zone, and there's one idiot blocking the fast lane who thinks it's a wonderful idea to pass them doing 55.00000001 mph.
Those idiots want to "Meter" the flow of traffic.
They're self appointed speed cops who want the entire highway behind them to follow at their speed. It's why they sit in the #1 lane, (fast lane) forcing everyone else to maintain their speed. They do nothing but cause severe collisions as everyone behind them is changing lanes jockeying to get around them. Those folks should be dunked in barrels of snot.