The movie is set in the late 1940s, when Los Angeles had a viable public transit system called the "Red Cars." These were electric trolley cars, like they have in San Francisco. One could live in Los Angeles without a car, like most other major metropolitan cities in the United States. The villain of Who Framed Roger Rabbit? is a creepy guy named Judge Doom (played by Christopher Lloyd). Over the course of the movie, we discover that Doom is actually the owner of an automobile company who buys out the "Red Cars" so he can destroy them and make everyone buy cars.
It's easy to miss the significance of this as a kid watching slapstick cartoon comedy, but watching it as an adult, the film is thick with social significance. What Doom fails to achieve in the movie ACTUALLY HAPPENED in the real Los Angeles. Beginning in the 1940s, General Motors subsidiary company Pacific City Lines (with investment from Firestone Tires, Standard Oil, Phillips Petroleum, Mack Trucks, and the Federal Engineering Corporation) actually bought out the Los Angeles "Red Cars" and dismantled them, forcing most people to buy cars. The beginning of the "car culture" of Los Angeles, and the reason why LA has such a shitty public transit system (and massive pollution) today is largely because of this.
Doom not only plans to dismantle the "Red Cars," he also plans to buy Toon Town (where all the toons live) and destroy it with a toxic mixture called "The Dip" and build a new thing called a "freeway." Toward the end of the film, Doom gives an apocalyptic vision of the future of Los Angeles: cars, freeways, billboards, air thick with exhaust. He is basically describing contemporary LA. The point of the movie "Who Framed Roger Rabbit" seems to be that it didn't have to be this way. If things had happened differently, we all might be riding the Red Cars.