The original note, as written at the time
All heavy vehicles (saloons upwards) should use highways below the city. Only light and quiet low speed vehicles should be allowed above the ground surface of the city.
Ongoing development
All heavy vehicles — saloons upwards — should use highways below the city. Only light, quiet, low-speed vehicles should be allowed above the ground surface.
This is a clearer policy than the usual “ban cars” argument, because it does not ban anything. It classifies, and the classification is by mass and noise rather than by ownership or fuel.
Mass is the right variable. A street is destroyed by weight, made dangerous by speed, and made unpleasant by noise, and all three correlate with mass far better than with engine type. An electric SUV is quiet and still ruins a street.
The hard question is the boundary, and it should be set low. A saloon is already 1,500 kilograms, which is twenty-five times a person on a bicycle. Any vehicle above a few hundred kilograms belongs underneath, and the exceptions should be for access rather than for travel — a delivery to a door, not a journey across a district.
The consequence is that the surface becomes a place for small machines: bicycles, scooters, carts, microcars, and walking. That is a street with a completely different risk profile, because a collision at those masses and speeds is survivable.
The cost is enormous and it is honest: a tunnel network under a city is generational infrastructure. So the policy is not a plan for a decade. It is a constraint on every street project in between — build the surface for the light, and never design it for the heavy.
Decide who the street is for by deciding what it can carry.