Ruled out alcohol? What about the likely biggest threat: cellphones? There are other possible explanations, but most of the lane-migrating I've seen has been due to fucking phones. Check her Facebooks, SMS, etc, and see what she was doing around the time of the crash. If she was, charge her. I'll be honest and say I haven't been innocent of the crime, but my process is usually: Can it wait? If yes, fuck it. If no, is there any traffic around that deserves my attention? If yes fuck it. If no, a majority of my attention still goes to the fucking road, unless there's a stoplight coming up which I'll wait for. The no-phone-while-driving laws don't really change anything, but I'm glad they're on the books simply so there's something additional to charge people with when they fuck up, assuming an investigation is even done. I'd like to see phones' radios disabled over a certain speed.