Working on a construction site that contains a railroad track requires proper permitting. A good engineer on a project will already know what permits are required, but sometimes you may have to do it yourself. A flagger will be required. Those costs must be accounted for in your job bid.
Jeff Spencer discusses permitting, the difficulties and technicalities of boring beneath a railroad, the holdups that occur when a train comes through. The guys have a laugh (as usual), but this is a serious topic that can result in very substantial fines.
From ProfitDig - easy job bidding for construction contractors.