Roads don't just emanate out of nowhere either. They must be built and maintained, or they become useless. I doubt building new highways really takes much less time than building new railways.

We wouldn't need to build new highways for this. We'd just be changing how we use existing ones (replacing existing road traffic with more efficient road traffic).

Which will wear down bridges and streets far faster. There have been experiments with extra long trucks in Germany, but so far they haven't resulted in extended regulations. Longer trucks have severe limits of manouverability in small cities.

It's all of this but mostly the flexibility. Rail is a centralized service with unpredictable schedules. Once a truck is full it can be shipped, but rail poses an additional bottleneck. Plus then you also need a driver on the other end anyway to pick up and deliver the trailer.

Rail should absolutely be used more frequently. It just isn't well integrated with trucking right now.

In India we have Ro-Ro (or whatever it is called now) where trucks are loaded onto trains and transported over long distance, fast and cheap. Then the roads take them last 100 km or so, in the heartlands (or wherever the destination). Best of both worlds.

We do the same thing in the US for more long haul things. Also we ship a lot of intermodal containers this way.

The big issue is speed. Individual trucks moving trailers is insanely fast. Semi's are commonly moving at 110km/h here in the states. The US is highly dependant on JIT shipping so any changes to slow this down would have huge economic impacts (which we saw with covid).