Network Rail deal with dozens of reports of earthworks failures, landslips, vehicle strikes, and other problems affecting bridges and viaducts every day. They have well-tested procedures in place to investigate them. In some locations, and at some times of day, those procedures involve on-call staff.

Sure, "just follow the process" is a lot less exciting than coming up with an ad-hoc response - but when you're dealing with safety-critical infrastructure at scale, it makes a lot more sense than cowboying it and hoping for the best.