No, modern train cannot travel on old railroad.
Step-by-step explanation:
In rail transport, track gauge is the spacing of the rails on a railway track and is measured between the inner faces of the load-bearing rails.
Most of the modern train are based on broad gauge. The separation in broad gauge is about 5 ft and 6 inches and in the standard gauge the separation between the tracks is 4 ft and inches. So for the modern train it is not possible to travel on the tracks whose separation is no more than 4.5 feet.
