The answer is: “because the other lane is actually more rapid”. And you can jump from one lane to the other without changing anything to it. Whatever you do, you will still be iost of the time in the slowest lane.It is the high density of a lane that makes it slow, because anybody adjusts the speed of his car according to the distance to the front car. For the same reason, the traffic is the most rapid where it is least dense, because there the distance to the front car is the largest. If you take a snapshop of a traffic jam from a helicopter and count the cars, you will necessarily find more slow cars than rapid cars.
Suppose that the slow lanes contain 2/3 of the cars and the quick lane 1/3. Every driver is alternatively in a quick and in a slow lane, particularly if he keeps jumping from one to another. As the fraction of slow and rapid cars is 2/3 and 1/3, a driver spends 2/3 of the time in a slow lane and only 1/3 in a rapid lane.
When you look at the other lane, 2 times out of 3 it will be more rapid than yours.
