> If we were designing the interstate system today, that's actually a fun thought experiment. What would we change? I would probably focus more on throughput -- cars can be half as wide and still seat tons of people, 5 lane highways today could easy be 8 lanes of narrower cars.

Why would you go narrower? That makes problems worse for trucks and other cargo conveyance; note that in general, newer highway standards tends to increase lane width, not decrease them compared to older standards.

(I guess you can see the same effect with railroads--the UK railroads have smaller loading gauges than newer networks like the US, Germany, or Sweden).