Wouldn't the railways be easily disrupted by enemy forces though? Missiles or bombers, and you only need to destroy one bridge or viaduct to render the long network unusable for a long time.
Railroads take just hours to repair if load bearing elements of a bridge are not damaged. Railway bridges are
much harder to destroy than most expect.
and total width 14 meters. Only a penetrating hit on the load bearing part will collapse the structure by definition.
CEP of PGMs is ~5 meters. However, the error distribution is not a perfect circle. Ranging is more difficult to get right than angular direction. This means that its easier to hit the bridge parallel to the rail than perpendicular to the rail. However that means for gravity bombing, you need to fly parallel to the rail, which is easy to predict, and air defenses can be laid in ambush.
If you fly perpendicular to the rail, the flight path is less predictable, but then you have to deal with the increased range error.
A railway bridge is made of reinforced concrete. That means normal semi-armor piercing warheads are unlikely to be effective. Here's what a non-effective hit looks like: a 3000 kg primitive 'missile' (a kamikaze plane) crashing into just 25 mm of steel plating does nothing but slightly burn the paint.
While carbon steel has tensile and compressive strength ~10x higher than concrete, concrete piles are also 6.5 meter thick rather than 0.025 meters thick.
So it looks like you need a bunker buster. These are very heavy munitions. What kind of range do they have?
. Its range is ~15 km. Heavier ones have less range. These severely cut into range and air to air loadout for strike fighters, while requiring strategic bombers to approach to basically point blank range.
So how would anyone attack Chinese bridge infrastructure? The only way is to attain air supremacy - even air superiority won't do, as even inferior PAVN fighters in Vietnam were able to force F-4s to drop their strike payloads.
Attaining air supremacy over Russia or China - something they could not even do against tiny Vietnam - is unlikely.