>Businesses have parking based on how busy they are,

Not really, no. Businesses are required to have minimum numbers of parking spots based on the square footage of the business, and a ratio determined by business type. A big box store in Tulsa needs at least 2.5 parking spots per 1,000 square feet of retail space source. That's about 500 square feet for the parking space and the adjacent aisle space, for every 1,000 feet of retail space.

In many cities, even a bar needs a parking space for every 100 square feet of interior space. A standard parking spot is bigger than that. And that's a bar, a place where people are expected to drink and therefore probably shouldn't be driving, and yet more space is devoted to parking than to the bar itself. Parking minimums are a huge waste of space.

In that first link, you'll find an analysis of parking spaces at a mall in Black Friday, the busiest shopping day of the year. Less than half the spots are used. So the parking lot could be half the size and still do its job. But because of parking minimums, we require that space to be wasted (and worse, covered in impermeable asphalt and prevents drainage and contributes to the urban heat island).

>Try about 2.5x for older cities) geographically constrained ones.

This is probably more accurate for older cities, I agree. Especially as older cities also tend to not have parking minimums for most of the dense parts, and most of these cities are more walkable and have better transit, so cars aren't required. And yet, that's still a lot of space. If every parking spot is 16'x8' (standard for a lot but on-street parking is usually about 13x6), that's 320 square feet for each car. The average person lives in about 450 square feet of space. Our cars need almost as much space as we do, that's absurd.

www.strongtowns.org/journal/2019/11/27/parking-dominates-our-cities-but-do-we-really-see-it

8 is the upper end of the estimate. Of course they're not actually reserved. But the US has parking minimums that require a parking spot per area of a business (ratio depends on type of business). Many businesses will threaten to tow your car if you park there and aren't a customer (as with everything, enforcement varies). So in essence they are reserved. Most workplaces have employee lots with enough parking for all their employees to drive alone. In rural areas, this is a reasonable assumption. In urban areas, it is not. (Well, actually most urban areas in the US still have a driving mode share of 90% or higher, so it is a reasonable assumption, but it really shouldn't be, given how inefficient cars are.)

If you're looking at just the cost of driving it, yeah. But the space in cities reserved for parking has a huge societal cost.

Taxis and rideshares take up very little parking because they're more often on the move (at least 40 hours per week), and when they park it's generally at either the home of the driver or a designated lot somewhere not central enough to have high land value.

Personal cars are only in use about 10 hours a week on average (and median is probably 6 hours a week), meaning they need storage the other 96% of the time. But not just one storage spot: one at home, one at work, one at stores, one at restaurants. In the US there are about 8 parking spots per car, and that doesn't include non-restricted residential parking (your driveway or yard, as compared to an apartment complex with a set number of spaces). The main solution here is to reduce or abolish parking minimums because most of these parking spots are empty most of the time, and even big lots at malls aren't full during holiday shopping, and unfortunately even places whose clientele doesn't arrive by car are often mandated to provide parking. But for every personal car given up where the owner uses rideshares and taxis, they're saving the need for about 8 parking spots overall (ok, really like 3, and the other 5 should never have existed anyway).

In theory, rideshares would require commercial drivers licenses, and therefore a higher bar of competency than we see today. Changing from personal driving to rideshares would reduce crashes, injuries and deaths, as a larger percentage of all drivers would be better trained. But honestly, all driving requirements for everyone should be higher. It's terrifying how little competence is required to be a licensed driver.