The Commerce Clause and the judgements that enforced federal preeminence over interstate trade in goods gave us a national single market in long-distance transportation. Powerful incentives for states to take from the whole to make some of their own better have been reined in by Congress’ periodic reassertion that it, not the states, decides when enough is enough.
Press release: What’s Up and Coming in Railway Safety Technology 
Image credit: Markik 
- “What’s Up and Coming in Railway Safety Technology”: https://www.rstreet.org/2020/02/03/whats-up-and-coming-in-railway-safety-technology/
- “Markik”: https://www.shutterstock.com/g/Markik