I'm also having this issue but on a different quest called "Ad Victoriam", it's a brotherhood of steel quest, *spoiler* I have to follow a huge robot we built in order to attack the institute. Here's the location on the map where it happens: http://prntscr. com/ 92eyzz (remove spaces) . I've tried going around but whole area is like that. I've also tried reverting back to an earlier save (got one with the previous quest) but as soon as I fast travel to this area it crashes. I've already had to become unfriendly with institute in order to advance a bugged quest, and now this. Glad we have to pay for an untested game
EDIT: Was able to fast travel to the police station and go back from there and I skipped 2 stages of the quest, the robot keeps doing it's thing and opens the entrance regardless of quest stage. Hopefully I never have to come to this area again. Nor will I ever pick up a game from bethesda at launch, this feels like an alpha stage game