I suggested something similar to this years ago, on various forums, and now it's in FE books. I don't drive on the line, though, because it makes the car drift, and it's usually really rough on the other side. All the roads I've driven on are much smoother outside of the ruts, and ridges created by the ruts. When there's no oncoming traffic, I drive left of the ruts and ridges, otherwise I go to the right.
I noticed white lines have low traction when wet even at red lights my tires slip for an instant as I travel over the white lines from a stop. It would make sense that they offer a less friction ride but some cars may activate the traction control causing the brakes to apply sensing one tire is slower than the other. I don't ride the white lines because of all the road trash/junk build up from the line outward to the dirt. lots of stuff that could cause a flat tire.
most of the Del. roads are very well kept. when it rains there's no deep ridges to fill up with water, I usually stay in the lane following the cars tracks in front of me. Their car splashes all the water out of the ridge so my car tracks in the almost dry ridge vs a filled up ridge.
The Motorcycle Safety Foundation states this in their rider course manual under the "Rain-slick surface" section.
"... Metal covers, bridge gratings, train tracks, painted/taped lines, leaves, and wood can be very treacherous when wet."
There is also a noticable difference in traction when dry. As a motorcyclist I try to avoid any turns or stopping when crossing a painted surface/line. Those big turn arrows near intersections cover enough ground to pose a hazard. I always try to avoid riding on a painted line or surface if possible on a bike or in car, traction and thus safety is compromised.
Just as Ford Man states I try not to ride in the middle of the road where the oil build up is, but here on the freeway it is not that bad unless it is wet. (As the song says "It never rains in sunny southern California !") Surface streets and intersections tend to have more oil build up and those tend to be a little worse.