Rail transit only makes sense in the largest cities, with concentrated downtown districts.

Most rail transit is built to serve the downtown business districts in cities. But the days when downtowns functioned as the primary centers of employment are long gone. Since about 1955, when people and office equipment began taking up more space, most new jobs have been created in industrial parks and small office parks–areas outside of downtown. Now, less than 10 percent of the nation’s employment in metropolitan areas is located in the old central business districts. So for more than 90 percent of commuters, rail transit isn’t an option.

Yet this fact is not an argument for extending rail transit into the suburbs. Employment outside of downtown areas is spread too thin to support rail transit. And any system serving the suburbs would have to include an expansive shuttle network to ferry commuters from transit stops to their homes or offices. So far, commuters have shown little interest in such a system.