Okay, I admit, transit by car is efficient
if a your car does not sit in your garage 3/4 of the time, and if your car stops to pick up other people with a destination on the same route instead of only carrying you, and if your car is 100% autononomous instead of subject to human emotions like jealousy, anger, and fear>>17549214
Yes, I know, it's a train with detachable cars, but worse in order to accomodate america's already shitty car-reliant urban planning.
I get the point of using the existing road network, but the existing road network will see major redesigns, diets, expansions, removals, and additions in half of our lifetime. Playing the long game, you should disregard today's road network and think about how cities will be or could be retrofitted in the future, especially when you get into major infrastructure projects like one-lane tunnel highways.
Which, by the way, are unecessary if you have self driving cars that can actually use a highway properly. No need to dig tunnels and discourage inefficiently driving from humans fighting over lanes if your cars can treat lanes as tunnels. Well, there are always per-lane exits, but a very minor road redesign would solve that. Temporarily widen the road and put an off-ramp or on-ramp right in the middle of it for that lane. Only works for bridges or surface streets that link with something underground, but hey, let's say that underground road is another road and not a fucking tunnel>but integrating with existing traffic
Get rid of existing traffic.