To preserve mass transit (e.g. electric trolleys) you need to compare the cost of housing with the cost of commuting.
That would have required high gasoline prices through the 1930s, 1940s and 1950s. If middle class and working class people could not afford automobiles, they would remain dependent on mass transit.
Have you heard the expression "Drive until you can afford to buy a house?"
Last year, a Vancouver journalist compared housing prices with commuting prices. Assuming that two house-buyers work in downtown Vancouver, the wealthier one purchases a downtown condominium for more than a million dollars, then cannot afford a car, so walks or takes a bus/trolley/Skytrain to work.
OTOH the buyer with the smaller annual income is forced to buy a multi-hundred-thousand dollar house in Surrey or Langley and commute more than an hour every morning and evening. After 20 years, his combined mortgage and automobile costs equal the money spent by the first buyer.
Over the years, Vancouver has operated a variety of street cars, trolleys, trolley buses, gasoline buses, diesel buses, diesel-electric hybrid buses, natural gas buses, SkyTrain, Sea Bus, etc. The city street grid was laid out - during the 1880s - to facilitate street car routes. Consequently, construction flourished along streets served by electric street cars. Street car rails were buried or removed during the 1930s, when gasoline prices were at an all time low. But wheeled trolley buses still work the busiest routes along Broadway, etc. Sky Train mostly runs along elevated rails, but dives underground through downtown and under False Creek. Wealthy residents blocked Sky Train installation in Shaughnessy, so Sky Train was forced to tunnel under those mansions.
These days, construction still booms along the newest Evergreen Sky Train line, with dozens of tall apartment buildings growing near new Sky Train stations.
All forms of mass transit are heavily subsidized in Vancouver because they are less expensive than building enough roads for everyone to drive to work.
Yes, you still need regular roads for limousines, taxis, ambulances, fire trucks, delivery trucks, etc. but smart truck drivers quickly learn to time deliveries to avoid sitting in rush hour traffic. The busiest grocery stores only accept deliveries during off-peak hours and only restock shelves late at night. Similarly, big city garbage trucks do the bulk of their work after peak business hours.