Trying for left 4 dead 2 bridge of trebled water achievement

[Reiki Knight 13 1,466]

I'm trying for the left 4 dead 2 achievement: bridge over trebled water and even on easy mode I keep running into tanks, hunters, etc that keep slowing.me down.

any good tips on how to try to get past it as fast as possible?

also, I'm playing with bots alone if you're wondering.