Mayor Rahm Emanuel is beginning his official search for firms to help turn his vision for a high-speed O’Hare express train from dream to reality. Today, City Hall along with the Chicago Infrastructure Trust will issue a formal Request For Qualifications (RFQ) seeking companies to design, build, finance, operate, and maintain the new service.

An express link between downtown Chicago and its busiest international airport was first proposed by former Mayor Richard M. Daley in the early 1990s. The concept was more recently revived by Emanuel as a second term objective with the announcement of a feasibility study in early 2016. The results have apparently provided the administration with the confidence to move forward with the FRQ.

While Chicago already offers reliable rail access to O’Hare via the CTA’s Blue Line, it is hoped that a high-speed express connection could cut travel times in half—down to roughly 20 minutes. A ticket would cost more than the CTA but would substantially undercut the price of taxis or other ride-hailing services.

As far as routes are concerned, the City is reportedly exploring several potential corridors both above or below surface ground. Deputy Mayor Bob Rivkin tells the Chicago Sun-Times that the existing CTA Blue Line tracks, the Metra’s North Central Line, and freight right-of-ways are possibly in play for the high-speed system.

This summer, Chicago officials also engaged in talks with Elon Musk’s Boring Company for a futuristic tunnel-based service that would utilize electromagnetic “sleds” traveling at speeds of up to 125 mph. Officials have not ruled out such a system should Musk or another innovative technology company answer the call.

The City is reportedly also open to the idea of utilizing the completed but never used $200 million Block 37 super-station in the Loop. An upcoming press event announcing the RFQ may even take place within the cavernous subterranean space.

Though the O’Hare express is expected to cost billions of dollars, the City still insists that it will not rely on any taxpayer-derived funds. It is hoped that ride fares, advertising space, and other “project-specific revenues” will entice a private operator to foot the ten-figure bill.

Responses to the RFQ are due on January 24th. So far, there’s no timeline for when the City is expected to select the most qualified respondent or break ground on the costly infrastructure megaproject.