Exit the safe room and enter the tunnels. Take the time to check around corners and in the side rooms – there will probably be health and explosives lying around. Wait and collect yourselves before you exit the tunnel – it is a great place to get ambushed, so you'll want to move as fast as you can out of the clearing and on to the path. Stay near the middle, as before, and watch for hunters and smokers lurking in the underbrush.There may also be goodies lying around, so keep your eyes open, but don't wait too long.
At the end of the path there will be a building in the side of the hill. Check quickly for consumables, then go inside. Once down the stairs, check the side rooms for more health and explosives – this is a good place to stock up. You will exit the building into another train tunnel. Follow the tracks out, and check the big tin building on your right for ammo and weapons. Keep following the train tracks. There is just the right of amount of open space and blind corners to make this a special infested feasting zone, so don't stop moving unless you have to.
After you pass under the bridge, enter the house on the left – there will be health and possibly ammo there. This is a fairly safe place to heal up if you need to. Head to the end of the tracks and trigger the event. Fight with you back against a train car and you should have no problem – the infected will come running across a lot of open space so you have time to kill them. Once the event is finished, hurry back to the bridge, on to the now familiar forest path, and into the safe house. Stay together and you should have no problems.