Driving on the Charles?

The weather in Boston has finally warmed up. For a while it looked like it would never get above freezing. The prolonged cold was enough to freeze the surface of the Charles River, which divides Boston from Cambridge. Some Harvard students, who are of course smarter than people like me, actually tried to cross the Charles on foot. It might not have been the brightest idea, but riddle me this: Are those tire tracks out there?

I took this picture from the BU Law Tower a couple days ago. I still can’t figure out what would have caused these tracks, which seem to go from around the BU bridge to the Harvard bridge. The tracks didn’t appear to be parallel near the bridges, but it was hard to see. Here’s a closer picture:

Judging by the size of the truck going across the Harvard Bridge, the tracks are way too big to be tire marks. Any thoughts?