In the safe room, collect replacement first aid kits and other weapons. There is also likely to be grenades in the safe room; collect those as well. The region until the next group of weapons will be a long canyon with good visibility, making long-range weapons ideal.
When you open the door and turn left, the light at the end of the tunnel will be blinding. You can regain visibility by standing behind a few objects, or by advancing to the tunnel's exit. The stream continues for a while until you see a ramp on the right. When the ground shakes, watch out for the tank on the cliff above that throws a few large boulders into the canyon, followed by jumping down. Once it is dealt with, you can climb the ladder to the ramps, and collect better weapons and more medkits.
From here, follow the path between the road and stream. You will turn towards the stream towards the jeep, climb back onto the road before the burning wreckage. On the road, climb over the gate by crossing the backs of a few trucks. With a flaming truck crashed on the road, you now need to jump back into the stream.
The bridge in front is fenced off, with the only entrance on the left. To exit on the other side, you need to shoot the barrels. When they start burning, backup before they explode, and fight off the horde that approaches. There may be a medkit next to the tent, so don't forget to search before destoying the barrels.
Climb down the bridge, and enter the large drain. Past the set of bars and near the end is a doorway that leads to a spiral staircase that leads to the saferoom.