Re: Would someone explain
If this were strictly enforced in the US for left turns, there'd be massive gridlock. The department of transportation designs intersections and include left turn lanes that'll sometimes hold 10-15 waiting cars, only allow turns while the green arrow is lit, and then only turn on the left turn arrow for 5 seconds. At some intersections, the first 3-4 seconds of your left turn arrow is taken up waiting for cars to complete the left turns from the cross street that they were unable to complete resulting in only 2-3 cars actually being able to turn left and leaving the rest in the left turn lane stuck until the next cycle.
I'm a proponent of shortening the entire cycle. Some of the cause for cars not being able to turn is obviously drivers farting around on their cellphones but another is having red/green cycles that are several minutes long. Drivers get inattentive when sitting that long at a red light especially those who get stuck in the left turn lanes staring at a red turn arrow. I think the goal should be to keep cars moving as much as possible---not have cars line up for several minutes at a time and then restrict their ability to make turns for only a few seconds.
Traffic circles help but is nearly impossible to replace existing traffic lights with traffic circles in urban areas. In rural areas, they're great. There's nothing so annoying as sitting at a red light in the middle of freakin' nowhere in the wee hours knowing that the second you decide to run through it -- because you can see that there's nobody coming for a mile in either direction -- will be when a trooper appears from behind a row of bushes and nails you.