[Goose]

Why is it so superior to transport supplies via rail than via roads?  Seems like the Russian air force should be able to knock out fixed rail infrastructure even more readily than it could attack vehicles traveling on roads and highways.  This is just my "common sense" observation, which I gather is incorrect, but I am not sure about the reasons.

Your common sense is actually somewhat correct. Electrified railroads are very vulnerable to damage of the catenary and even more so to damage of the substations that supply power to the line. No volts, nothing moves. Self-generating locomotives don't have this problem and are therefore preferred in situations where power stability is an issue.

The preference for rail transport is actually "commercial". One freight train can carry as much ammunition (or anything else) as many trucks. The railroad delivered goods do then need to be transshipped to trucks to reach the "end user". That isn't as much of a problem as it seems because goods transported by trucks usually are unloaded at a supply point and then transshipped in the same manner. The big "over the road" trucks are not suitable for delivering things in a combat zone. Obviously running 500 or more truckloads to replace a trainload requires many more personnel. It also requires maintaining many prime movers (instead of one) and consumes much more fuel. The big advantage of trucks is that if one is destroyed the others can still get through. If a train is destroyed, none of it arrives.

While shooting up a train or truck convoy is useful (and sometimes spectacular) the most lucrative targets are road and rail bridges. You can shut down transit completely for a very long time that way. As far as blowing up the road or the railroad tracks themselves neither approach works real well. Both are easily repaired, although repairing railroad tracks is actually easier than repairing the road in most cases. Prefab rail sections are very common. Fill in the hole and put down the prefab section and you are done. Many times BDA of North Vietnamese railroads showed no damage at all because the line was repaired in less than an hour. The recon flights would take pictures of the repaired railroad.

[Goose]

Why is it so superior to transport supplies via rail than via roads?  Seems like the Russian air force should be able to knock out fixed rail infrastructure even more readily than it could attack vehicles traveling on roads and highways.  This is just my "common sense" observation, which I gather is incorrect, but I am not sure about the reasons.

Your common sense is actually somewhat correct. Electrified railroads are very vulnerable to damage of the catenary and even more so to damage of the substations that supply power to the line. No volts, nothing moves. Self-generating locomotives don't have this problem and are therefore preferred in situations where power stability is an issue.

The preference for rail transport is actually "commercial". One freight train can carry as much ammunition (or anything else) as many trucks. The railroad delivered goods do then need to be transshipped to trucks to reach the "end user". That isn't as much of a problem as it seems because goods transported by trucks usually are unloaded at a supply point and then transshipped in the same manner. The big "over the road" trucks are not suitable for delivering things in a combat zone. Obviously running 500 or more truckloads to replace a trainload requires many more personnel. It also requires maintaining many prime movers (instead of one) and consumes much more fuel. The big advantage of trucks is that if one is destroyed the others can still get through. If a train is destroyed, none of it arrives.

While shooting up a train or truck convoy is useful (and sometimes spectacular) the most lucrative targets are road and rail bridges. You can shut down transit completely for a very long time that way. As far as blowing up the road or the railroad tracks themselves neither approach works real well. Both are easily repaired, although repairing railroad tracks is actually easier than repairing the road in most cases. Prefab rail sections are very common. Fill in the hole and put down the prefab section and you are done. Many times BDA of North Vietnamese railroads showed no damage at all because the line was repaired in less than an hour. The recon flights would take pictures of the repaired railroad.