From the efficiency of the urban commute to the romance of a ride through the country, our rail systems keep us moving. With just shy of 3.6 billion riders on subway trains alone each year, an aging infrastructure demands attention, and spells opportunity for investors.

Full steam ahead
From the Chicago L to the DC Metro, from the NY/NJ Path to the Portland MAX, light, high-speed, and urban rails throughout the country are expanding, upgrading, and maintaining vast rail networks. Presently, most of the companies manufacturing rail cars are located overseas; however, many are traded on the U.S. exchanges.

The House of Representatives introduced a bill calling for made-in-America rail infrastructure this past April. President Obama's plan for the FY2012 budget included $53 billion over six years for intercity rail. While the outcomes of these initiatives are uncertain, one thing remains clear: Momentum is building for nationally sourced infrastructure.

With soaring gas prices driving many drivers into ridership, a renewed commitment to revitalizing the country's transportation infrastructure, and many subway cars on systems throughout the country aging out of usefulness and safety, the train manufacturing business looks primed for growth.

From coast to coast
Back in the '70s, Boeing (NYSE: BA) built the bulk of the Chicago L trains, before it realized that airplanes were more profitable. Many of those original cars are still in service on the Green and Purple lines. Because most subway cars have a life expectancy of 25-40 years (accounting for maintenance and refurbishment), expect the Chicago Transit Authority to replace them in the next several years.

Washington, D.C. is another perfect example. Last year, Metro signed a contract for 648 new subway cars, at $3 million per car. In addition to replacing aged cars, the system is adding a line westward to Dulles International Airport. Although Goodrich (NYSE: GR) made many of the original Washington, D.C. Metro cars, Kawasaki (PINK:KWHIY) will supply the newly redesigned cars rolling out this year. Metro will award another contract in 2019.

A new player?
GE Transportation
(NYSE: GE) has recently announced a new plant in Texas that will focus exclusively on train manufacturing. (GE Chairman and CEO Jeffrey Immelt also serves as the White House's Council on Jobs and Competitiveness, which might just help his company land a few contracts for public rail projects.) Sadly, this plant will be too late to fill the Houston Metro's order of 19 subway cars, which just went to Siemens (NYSE: SI), or an order for Orlando, Fla.'s Sunrail, which went to Bombardier (TSE: BBD.B).

GE's newly amped-up presence will no doubt encourage other domestic manufacturers to join the competition. Add to that the sheer volume of subway systems and moving stock throughout the country, and all their required maintenance, parts, and service, and you're looking at a steady, consistent industry that is set to thrive domestically.

Want to keep an eye on the companies mentioned? Add Boeing, Kawasaki Heavy Industries, Goodrich, General Electric, and Siemens AG to My Watchlist.

Never think twice about the cars on the trains near you? I challenge you to find out. Tell me your town, line, and car manufacturer in the comments below.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.