Left 4 Dead/The Turnpike

You are outside the city, behind a police car. You need to travel through an underground road tunnel to reach the safe house.

Paths
At the beginning, you will head forward to the broken bridge. Climb up the ladder on either the left or right side.

After climbing the ladder, you will proceed down the tunnel and across some cars and trucks. Eventually, the direct path will be blocked, but a side passage will allow you to reach an alternate exit.

In the following room two story room, the exit on the right may contain a second pistol.

Exit the basement, and proceed onward to the safehouse.