spurReservation

The transporter that has reserved this spur so that it can get back out, or null.

A dead end has to be entered and left by the same way. A transporter sent to the far end of a spur therefore keeps the whole spur to itself for as long as it is down there: another transporter sent to the same place would have nowhere to pass, and the two would face each other with neither able to move. Traffic merely passing through the mouth of the spur is unaffected, which is the distinction that lets a spur keep a stopped transporter out of the way without also stopping everyone else.