Space is the main problem with cars, as it is inherent in the concept of the car, independent of the technology of its application. The space required by a vehicle is it's actual size, and the space in front of it that is required to be vacant to prevent collision, its right of way (ROW). For any static object a single car's ROW is the stopping distance times the width of the car, at 100 kph approximately 60 metres times 3, 180 m^2, this is the "space" an individual car requires. This fact alone is why a car system is so space inefficient compared with transit, and why car based cities are so much more expensive and less sustainable, each car adds one small house-plot of space to the city area, or deprives someone of that house-plot in places like Indonesia and China. This is literally reflected in new suburban development in the USA and Australia, 50% of the area is road or carpark.
Of course cars moving in convoy, in each other's slipstream, reduce their per capita ROW. Systems called "intelligent traffic systems" do this by lining them up either with remote control or an artful manipulation of traffic lights, at their best they can reduce the space demand by cars to be about as space efficient as unmanaged bicycles, and not as efficient as buses, trams or particularly trains. Also they remove the autonomy of the vehicle, at least temporarily, thus removing the only real advantage of cars over public transport. One can experience the inefficiency simply trying to walk across a highway at peak-hour, by the time a thousand people have passed one may have waited 10 minutes, alternately one may wait for a train, carrying 1000 people, to pass and be on one's way within a minute. Multiply this by all the roads and all the waits to recognise both the inefficiency and the impost on non-drivers. The space demanded by car transport has natural, social, economic and administrative disadvantages.
Practically the car reduces living space by even more than it directly appropriates in ROW, there is an ambit space appropriation, the noise and general unpleasantness of cars drive people out of their front yards and balconies. Many urban parks, visually idyllic with trees and lawns, have become little more than median strips, constant streams of traffic prevent easy pedestrian access or egress from the space and make it noisy and unpleasant to recline in. All the space near roads is increasingly developed for its visual appeal to drivers, not for human habitability. Habitable space is increasingly restricted to indoors and dedicated recreation space.
For space to be usable it must be accessible so interspace (the paths between spaces), is essential in any economy, however the traversal costs energy, and given that interspace is crossed often and often several interspaces must be crossed in each journey, a small increase in interspace radically increases the movement required. Thus the energy factor of a city is a case of classical time and motion study, whichever has the narrowest interspaces, provided they are adequate to allow movement, will be the most efficient, and the widest interspaces will be the least efficient and consume the most energy in traversal of interspace. Choosing an inefficient transport modality like the car inflates the distance of all "interspace" journeys within the urban area hence it inflates the time and energy expended in interaction.
According to the world's leading (or only) ecological accountant, Mathis Wakernagle, highly productive agricultural land yields 8 to 10 times the produce of average land. Because humans initially settle highly productive areas this is where cities are and they usually expand onto highly productive agricultural land in river valleys. In order to maintain agricultural production land is cleared at the other margin, the marginal, low productive land. This land yields produce at a rate about 1/10 of an average hectare or 1/100 of what the now urban hectares used to produce. Each urban car in Australia increases the urban area by approximately 100 square metres (see Landspace Economics) over and above what would be necessary in a non-car system. Thus one hundred square metres of urban expansion produces the clearance of 10,000 square metres of marginal land, the principle habitat of the world's remaining wildlife. This allows for an easily remembered equation. One urban car in Australia causes the clearance of one hectare of forest or scrubland, an area the size of 10 suburban houseplots. Because the urban car fleet is about 8 million this means they have cleared 8 million hectares of habitat.