[Piskvorrr]

1. Building railroads is an order of magnitude harder than building roads (gradients, turn radii, clearance, yards).

2. Not even building, just repurposing. "This road/lane/whatever now SDV only."

3. Trains only run on rails. Trucks that could be run as SDVs on dedicated infrastructure and as human-driven on shared infrastructure tackle the last-mile problem far more efficiently.

4. Trains are built on the "smart infrastructure" paradigm (go straight at the speed which the signals tell you, until the signals tell you to stop); trucks on the opposite "smart vehicles" paradigm (road exists, everything else is your responsibility). This makes a truck rollout far more scalable (as in "just add this road to whitelist").