Water Under the Bridge

It's Thursday again, and that means another puzzle:

Four people need to cross a bridge in the dark as fast as possible. Problem is, the bridge is old and rickety, which has the following implications:
1.The bridge can only support a maximum of two people at one time
2. Anyone crossing must be holding, or standing next to the person holding, the only flashlight they have between the four of them, (so they can see the holes in the bridge).

Due to varying levels of physical fitness, they can cross at different speeds. Alice is a sprinter, and she can cross in 1 minute flat. Bob does his Pilates, and cross in 2 minutes. Caroline is a bit rotund, and it takes her 5 minutes. Doug is very old, and it takes him a full ten minutes to maneuver his walker across the bridge. The problem is, when two people try to cross at the same time, they can only move as fast as the slower of the two. SOOOOOOO...What is the fastest time in which they can get everyone safely across?