If I recall, this whole idea started as a result of traffic on the 405 or something.

This idea is only useful if it could deliver traffic volumes at meaninful percentage of the current 405 throughput.

wikipedia says "The freeway's annual average daily traffic between exits 21 and 22 in Seal Beach reached 374,000 in 2008" .

So how many car elevators to do 10% of that? How many car elevators to move 37,000 vehicles per day? Assuming a 1 minute cycle time, that would be 25 elevators running 24/7 evenly, with no rush hour (obvious unrealistic).

I think it is a scale problem, much like 3D printers won't upset the economics of high speed injection molding anytime soon.