Really? That's not how I heard it.
Some high school boys set the bridge on fire a week before the exit. They did this because at the time Mosier Valley was predominately a black neighborhood (I also heard that it was done as a prank, so I don't know which is true), and the bridge linked MV to Arlington. Well the bridge didn't burn down completely, but it was damaged. Anyways, 6 girls from Arlington were in the area, and were being harassed by a bunch of bikers. They sped off down the road, not realizing that the bridge wasn't going to support their car. When they drove over it, it collapsed and I think 3 of them died on the scene, and another died at the hospital.
Back in 2007 I had come across some forum posts from people who went to high school with the girls. That's the story that I read on the forum, and that's how I found out the real location (one of them posted it).