Rain drop components

It rained very heavily all the way to London. I noticed the consistent angle of all the rain down the window on the motorway. If we were stationary in still air I would expect the rain drop trails to be vertical. At 60mph they were at a large angle to the vertical. I thought the angle would decrease when we slowed down in the city but that didn't seem to happen. I wonder if there is some sort of effect that once tracks get set across the glass, they become lines of least resistance that the water follows thereafter. More observations needed.