It's a lot simpler than that.
Only semi truck drivers use the weigh station, everyone else just drives on by. It's not a place that's going to attract much of anyone or anything. It's located in such a rural area, there are no homes nearby. It's an interstate, winding through a national forest, with a 100-acre private fenced farm behind the Weigh Station.
The occasional zombie won't be an issue, I'm sure.