Chicago has a classic hub-and-spoke transit system. It's a relic of another era, when all the employers were downtown, and all the workers in the region needed to flow in from surrounding communities in the morning and back out again at night.

As has been the case in cities all over the country, Chicago's job centers have long since scattered from the center of town. Jobs have moved to suburban office parks, or to hospital campuses in new neighborhoods, or to commercial strips around the airports. The geography of employment, however, invariably shifts faster than the ability of mass transit to keep up.

So what do you do if you're a city with a 100-year-old rail network that no longer takes many residents where they need to go, maybe across town instead of downtown, maybe out to the suburbs beyond the last stop? The answer in Chicago and elsewhere will be crucial to the economic health of the entire region for years to come. And the answer – anywhere – probably will be dramatic and expensive.

For perspective, this is what Chicago's elevated rail system looks like today:

And this is an alternate future for what it could become, from a map just proposed by a couple of transit advocacy groups, the Center for Neighborhood Technology and the Active Transportation Alliance:

Add bus systems (in purple) that would have the ability to bypass vehicle traffic on road shoulders, while coordinating with stoplights, and you get this:


The price tag for something like this – for extensions and modernization of the existing system, for new rail lines entirely bypassing downtown, for a bus rapid transit corridor running the length of the city, for the new high-speed bus service that would knit that network further into the suburbs – would require an investment of at least $20 billion.

This probably sounds unrealistic. But Chicago Mayor Rahm Emanuel and Cook County President Toni Preckwinkle turned up to speak at the event in Chicago on Thursday unveiling the campaign to seriously start looking for that money. The advocates behind this vision believe that the financing is possible, if Cook County would approve a local funding stream, as Los Angeles has – likely on the scale of a half-cent sales tax increase – that would then allow the city to tap into federal matching funds.

The campaign includes a strikingly savvy Web site to help sell the public on this plan, highlighting the 50,000 jobs that could be connected to the L in one South Side neighborhood, or the extensions that would link neighborhoods located close to O'Hare International Airport but that remain strangely dislocated from it.

Even if any of this never comes to pass, there's a value to wildly ambitious infrastructure proposals in an era when so many cities are wrangling over the fate of a few miles of streetcar. There's a value to pondering this hypothetical, or this one. This is how cities expand the debate from one about incremental new capacity to one about job access and real estate value and economic growth.