Easy - head toward the Key Bridge. The exit for the MVT is well signed located just before the bridge where N. Lynn St. crosses Lee Hwy. There is a bike and pedestrian bridge across the GW Parkway, ending in the parking lot for Theodore Roosevelt Island and the MVT goes south from there. I rode that way home on Thursday and Friday in perfect weather - not the shortest way home for me, but well worth it.

By the way, I mis-spoke. The trail on Rt. 27 branches off to join the MVT south of the Memorial Bridge, not north. You DON'T go under the bridge before the two trails join.