The road is out leading to the Shroud, but the turians can't divert from the Reaper now, it's too late to avoid a strike. The air forces alone aren't enough, and the Reaper starts tearing through them while we're all stuck on a bridge.

Shepard: WE WILL MAKE A GODDAMN ROAD IF WE HAVE TO
Shepard: JUST GO

But in the rush and the crashing turian jets and the exploding, Shepard's team has to find their own way there. Through the lost underground city of the ancient krogan! Unmapped and full of tremors! Sounds fun. Wrex thinks it sounds fun, anyway.