I actually thought the same till I looked at the Renraku Arcology floor listing. This is a building 780m by 650m 507,000 square metres in size or half a square kilomter (of which I think 6 floors are open to the public normally with tours accessing specific other ones) The basement has 5 floors dedicated solely to parking which means the arcology has somewhere in the region of 2.5 square kilometers of parking. Of course some of that is taken up by the bus station, m5 etc still that's a lot of room to park a car that on average will only take up an area 18.15 square meters. To put it another way the arcology has room for nearly 28,000 cars per floor, 140 thousand all up. Knock 20% off say for areas to drive said cars, bus stops, etc and you can still fit 112 thousand cars. The arcology according to its source book has 92 thousand permanent residents. So each resident can have a car park and still leave room for 20 thousand vistors to park their personal cars.
When I looked at those numbers it really started to sink in just how big this place is for me. Still lets adjust those to match my suggested parking alotments because I agree low income workers at least aren't going to have a parking spot as they couldn't use it in the arcology anyway but I can see a middle class family wanting one a spot to park a car even if they never use it. Anyway for the purposes of this I classified blue collar (the renraku arcology term) as low income. Which means my categories were low income/lifestyle (2,000 month), middle income/lifestyle (5,000 month), high lifestyle (10,000 month), executive/luxury income lifesetyle (100,000 month). Of course for the purposes of this post I've decided to change a classification because on thinking it over I feel executive belongs more in high rather than luxury especially since there are no high income floors and there are a lot of executive floors. I'm also tossing mages in with the high income floors although their levels are a mix of residence and workspace. However I'll count them as whole floors Taking that into account we get . . .
Total Arcology Floors: 320
Floors open to the general public: 7 (6 mall floors and 1 rooftop garden accessible via the 31st floor)
Floors on which tours operate: 8
Low Income Residential Floors: 64
Middle Income Residential Floors: 80
High/Executive/Mage Income Floors: 64
Luxury Income Floors: 9
Non-Residential Floors Not Open to the Public: 98
So that means the number of floors on which residents live who could expect a car space is 144 out of 320 or 48%. The floors open to the general public constitute 15 floors (being generous as only 7 are full floors the rest just run tours) out of 320 or 0.05% of the building. This means the amount of the building where parking is a concern is 48.05% with the rest being either too low income to possess one or a floor only accessible to residents used for non-residential purposes. So lets see how much our parking space equals in that case . . .
0.48 * 112,000 = 53,760
0.0005 * 112,000 = 56
Bear in mind that these basements would allow the full half a square kilometer of space for use. Now obviously 56 visitor spots is far, far too low for 7 general access floors totalling roughly 3.5 square kilometers and that doesn't even consider the tours. So we need to adjust things lets start by working out by floor what % of the population we need to worry about. Now what I think is a good way to determine this is to just use the residential floors not the whole arcology as we'd throw things off otherwise.
Residential Floors: 217
Middle Income +: 153
Low Income: 64
With these can see of the 92,000 people by floor roughly 29% (64/217) is low income and would have no spot while the other 71% (153/217) does. Of course the problem here is that you would have a higher amount relatively speaking on the lower floors as they'd have smaller residences and more people on their floors since the arcology narrows as it rises meaning fewer apartments. However I'm choosing to ignore this because these car spots are as I said not being assigned on a 1-1 basis e.g a luxury apartment actually taking up an equivilent of 4 spots for 1 person because they have a 3 car garage + storage. I digress though when we feed these values into the population we get . . .
29% of 92,000 = 27,132
71% of 92,000 = 64,866
So for our residents we need just under 67,000 car park's to cover them. We had 53 so lets be generous and bump the parking allotted up to 70,000. That means we are now looking at . . .
Resident Parking: 70,000 spots.
Visitor Parking: 42,000 spots.
That's a lot of visitor parking assuming some portion will be arriving via bus or train. Percentage wise this means we're looking at . . .
Parking levels allotted to public transport or ? (what do you call the space between two rows of parked cars people drive along? Its not a driveway is it?): 20%
Resident Parking: 50%
Visitor Parking: 30%
So lots of parking there to assign as carspots, garages and storage. Sure its only 5 floors out of 320 with portions of those floors being used for other purposes but its still a huge amount of parking in actual terms. At least for the Renraku Arcology and the Aztechnology one seems similar as while it only has a fraction of the population (5,000) and is somewhat smaller at 500 by 500 or 250,000 square meters (0.25 square kilomter) yet it still dedicates 3 whole floors of its basement to employee parking. That is roughly 33,000 parking spots (allowing as I said 20% of the space for driveways and other functions). The arcology only has 5,000 people living there a mere 0.15% of the available space assuming all of them got a spot (they are all middle income and up).
Going by those two there is a lot of space in the arcologies dedicated to employee and visitor parking so do my rough guidelines seem to work?