You need city governments to invest in busses, trains and subweays to the extent that it is cheaper for each individual to use them than to own a car.
You also need some way to PREVENT the rise of the suburban neiborhoods and housing projects and keep up the old style "Neighborhoods" such as were once the big thing in major cities.
Nah, what you need is at the most, Zoning boards forcing (and the market encouraging) developers to build streetcar suburbs, and in a fairly dense manner, like thirteen or so homes per Acre (43,560 square feet,) or a buildable one anyway (since a two lane road, with a 27-foot wide road, two driving lanes and a parking one @ 9ft each takes up some space) or about 3200 square feet per lot. Which is actually kinda generous for building Normal Bungalows, (since you're talking a 40ft by 80 foot lot, as was custom,) plenty of space for a 3bed 1bath home with a yard (sufficient for a family of four to six in this period, but capable of accommodating far more,) and a garage, if you're willing to build a 2 story structure (which is actually a good 15-25% cheaper per square foot to build since foundations are
expensive.
So, on an acre, you can squeeze in thirteen families totaling fifty to eighty people, in comfortable dwellings.
A 27 foot road is ofcourse the minimum unless you're planning on placing a driveway and a garage in every lot, so as to allow people to park on the street. If you're putting in all of that, you can safely shrink the road to 18 feet, (either way you will need a sidewalk though, which will cut buildable area by a bit, with a recommended minimum of 10 feet between the outside edge of the sidewalk and the curb, so it'll eat 38 to 47 feet.)
Of course, on that same lot, with Through Terraced houses, including the sidewalk, and everything placed properly (figure a 99 by 440 foot acre lot, a 38foot road bisecting the long side, thus creating two 99x201foot areas) you could fit 20 lots of 20x99 feet (1980 square foot footprint for each) figuring a 20x10 foot (200square feet) space out back, that's a 1780 square feet for the house, buildable up three or four stories easily, for 5340 sqft (3 stories) or 7120 sqft (4 stories) per building. Which is space for a hell of a lot of people, since that's space for a two car garage (and since two cars only takes up a 20' by 20' space, with 1300 sqft for a massive utility space) on the ground floor, with each floor above that be plenty of space for a 3bed/1bath unit. So, at 2 units per building (three stories, including the garage,) at 20 per acre, that's 120 bedrooms, capable of accommodating something like 160 to 240 people per acre.
But after all of that, with streetcar suburbs, you'd normally build everything so that the shops would be next to your stop, not more than say a thousand feet away, and would be fairly small by modern standards, since a Supermarket back in the fifties was between 10,000 and 25000 square feet (with the median @ ~15-16,000 sqft) while previously, a grocery would normally be under 10,000 sqft. Other Shops would generally be a bit smaller, and folks would do their shopping for goods like clothing in Department Stores, and the cheaper five and dimes, usually in centralized areas.
Keep that sort of Development pattern (hub and spoke pretty much) enshrined in city codes, and you could presumably keep the car marginalized long term.
