A common misconception I face is that I don’t like cars. On the contrary, cars are a wonderful thing: they give us freedom of movement, allowing us to go where we want, when we want. They are mobile rooms, so we can keep our stuff relatively safe wherever we go. They are personal mobility tools for people who have trouble walking. They’re a fabulous invention. But they use up too much damn space for everyone to use them.
Or, if you prefer, a diagram of the same, with each box sized according to the space used by a traveller in the mode:
[The data above assumes a Level of Service of D for pedestrians , bicycles , and cars ; 1.2 passengers average for cars; 1 passenger for other private modes; 66-passenger bus; and 2,000 riders on a 10-car subway train.* Bike parking assumes 2 spaces, the size of which were estimated from a 12,500-space bike parking garage in Utrecht ; car and motorcycle parking assumes 3 spaces, the size of which were estimated from planning documents [5a; 5b]; and bus parking assumes a typical maintenance and storage facility . Road space assumes 11-foot-wide urban lanes and 12-foot-wide freeway lanes.]
Jarrett Walker calls is this a problem of geometry: a dense city cannot run on cars . There just isn’t enough space for most people to use it as their primary mode of transportation. Buses, trains, bicycles, and walking all use less space, so they become primary. I’d argue this is not just a problem of dense cities but also of chokepoints within less-dense places.
The first thing I notice is how much parking is needed, especially for driverless and urban cars. It looks like over half the space needs for urban cars come from parking, and almost three-quarters of the driverless urban car needs are from parking.
The goal of transportation planners ought to be to maximize the usefulness of their space. Driverless cars will help cut down on road usage, but their parking needs will still eat up much of the landscape. Driverless taxis would help more, but to be as space-efficient as a half-full bus they would need an average load of 20 people, and at that point it’s more bus than taxi.
In comparison, a bicyclist uses just 7 percent the space of a driver in a city. Someone on foot uses less than 2 percent.
In practical terms, the various space-intensive modes travel should be the most rare ways of getting around, used for practical reasons by people with mobility issues, people who have unusually long or circuitous commutes, and people who have loads to move. Travel by other modes should be much more common, especially at times when a lot of people want to go to a relatively compact area of the region (like at rush hour). These other modes should be just as fast or faster than driving (accomplished by improving those other modes), and relying on them should not feel like a burden.
Far from making driving harder, inverting mode shares so driving becomes more rare would actually make driving easier and better by making other modes much easier and much better. There’s no reason to give away 2,300 square feet of space to every car traveler when 27 square feet by bus or 7 and a half feet by train would do just fine for most trips.
* Trains are the only vehicle here that must operate in their own right-of-way. They can move around 50,000 people per direction per hour using realistic headways compared with 4,800 on buses in their own right-of-way. Without stops, which would approximate the other modes' metrics, a train could operate about twice as often and yield the 7.5 square feet needed per passenger indicated here. A parallel article would examine lane capacity, but that would necessarily exclude parking - a key factor in cars' inefficiency - and so this is not the place for that examination.
 “Current HCM Methodology,” in Pedestrian Level of Service Study, Phase I (New York, NY: New York City DCP, 2006).
 Dan Zhou et al., “Estimating Capacity of Bicycle Path on Urban Roads in Hangzhou, China” (Conference Paper, The 94th Annual Meeting of the Transportation Research Board, Washington, DC, 2015).
 Energy Facility Site Evaluation Council, “Appendix C: Transportation,” in Kittitas Valley Wind Power Project Draft Environmental Impact Statement (Olympia, Washington: Sate of Washington, 2004).
 Juliana Neira, “World’s Largest Bike Parking Garage Opens in The Netherlands,” Designboom, August 10, 2017.
[5a] “Design and Improvement of Parking.,” Section 19.26.040, Roseville Municipal Code, accessed August 18, 2017; [5b] Peter Croft, “Light Vehicle Sizes and Dimensions: Street Survey Results and Parking Space Requirements – Information” (Auckland, New Zealand: Land Transport NZ, December 2004).
 Division of School Support, “School Bus Maintenance Facility Planner” (Raleigh, NC: North Carolina Department of Public Instruction, February 2011).
 Jarrett Walker, “Does Elon Musk Understand Urban Geometry?,” Human Transit, July 21, 2016.