The total distance for a train to cross a bridge is the length of the train plus the length of the bridge. Because the length of the previous two trains is the same, the distance between multiple lines is the difference of the length of the bridge, so (360-240)÷(28-20) = 15 (m/s) is used.

The vehicle length is equal to the distance minus the bridge length 15×20-240 =60 (meters).