That's technically true, but it assumes away the core, ever-present problems:
- It may not be physically possible to add enough lanes to e.g. handle everyone who would ever want to commute into L.A.
- Even if that road was correctly sized, it still has to dump the traffic into the next road, through the next intersection point. If you've increased the capacity of the freeway but none of smaller road networks that the traffic transitions to, you've just moved the bottleneck, not eliminated it. And that too may be physically impossible.
In any practical situation car transportation efficiency does not scale well enough that you can avoid addressing the demand side.
It isn't physically impossible to use eminent domain to seize all the property around the roads and then build 32 lane roads all over Los Angeles.
That is a separate question from how stupid that is in comparison to the alternative of building higher density residential housing closer to where people work and with better mass transit.
But if people don't want to do that either, you have to pick your poison.
And there really are many cases (Los Angeles notwithstanding) where adding one lane isn't enough but adding two is and where that genuinely is the most reasonable option.
Also, one thing that's often forgotten is that roads take up space. A lot of it. You make your roads bigger to accommodate more people, and all of your buildings wind up farther apart as a result. When buildings are farther apart you have to drive farther, meaning that everyone's journeys are longer, meaning more traffic... and on and on it goes.
I mean, at what point do you just build a 400 square mile skid pad with nothing else there just to "alleviate traffic"? Hell, that's practically what Orange County is already.
Assuming "parking spaces" include one's home space (like garage or reserved spot), 3 should be expected, at least: home, work, and wherever you're visiting.
Now assume Uber et al own fleets of self-driving 9-passenger minivans. During peak commuting hours they're completely full because they pick up different passengers who have the same commute, and that way you eliminate the parking space both at home and at work.
The rest of the day they don't actually park anywhere, they just stay on the road operating by carry one or two passengers at a time instead of eight or nine. Or half them stay on the road operating and the other half go off and park in some huge lot out where land is cheaper until demand picks up again.
Then instead of 3.3 spaces per car you can have <1, and most of them can be in low land cost areas.
It's actually kind of like dynamically allocated mass transit.
More likely scenario will be self driving cars cooperating with each other to drive from start to finish without any stops. Whether on freeways or local streets, cooperation amongst vehicles will raise the average speed and the volume of vehicles you can process through a given area. Pools work to a certain degree if everyone is starting and ending at the same location. When they don't, then it actually takes longer than driving by yourself.
Final point, you can certainly build out less parking spaces, but pre-existing spaces won't go away without redevelopment.
You're right -- I should have said "feasibly" rather than "physically" above. It's certainly physically possible, but requires a tradeoff I don't think many people would actually sign off on: blowing 3 years of budget for multi-deck freeway tunnels and having twelve-lane streets for most of the city, a parking garage for every block, and 95% of the city allocated to roads.
> It isn't physically impossible to use eminent domain to seize all the property around the roads and then build 32 lane roads all over Los Angeles.
This might be an extreme example that won't work for other reasons, but generally adding more lanes will increase demand, so you still won't have enough lanes.
- It may not be physically possible to add enough lanes to e.g. handle everyone who would ever want to commute into L.A.
- Even if that road was correctly sized, it still has to dump the traffic into the next road, through the next intersection point. If you've increased the capacity of the freeway but none of smaller road networks that the traffic transitions to, you've just moved the bottleneck, not eliminated it. And that too may be physically impossible.
In any practical situation car transportation efficiency does not scale well enough that you can avoid addressing the demand side.