The drawbridge is one of the intractable elements in Cold Comfort. Survivors can insert fuses in the fuse box in the control tower, flip the lever, and the drawbridge will go up. In Seneca for example, the Gamma Primes spawn on one side of the drawbridge, and when it is down, can easily traverse the bridge, quickly getting into the action. However, once the Survivors activate the drawbridge and it goes up, this particular path is blocked, forcing them to go into the canal, swim across, enter the sewers and slowly make their way back to the hot zone.
This particular model was done by the talented Ryan Kohr, make sure to check out some of his other work on his artstation page.