Driving the Travel Lane

Driving to work today. I normally commute via the train and that is
nice. But it is a 70 mile drive today. Raining. The wipers are going
back and forth. Fortunately most people are leaving the right lane open
again. I do not understand it. They travel at their speed in the middle
or passing lane and leave the travel lane open. At points where I am
allowed a view of the road ahead, one can observe the density of the
cars in the high speed lane and the middle lane. Both are almost bumper
to bumper with little space between the cars. Over here in the right
lane, I have it mostly to myself. Fine by me... makes for an easier
drive.