There are 96 miles of railroad track connecting the downtowns of Clearwater, St. Petersburg and Tampa. The steel grating links Tampa International Airport to the University of South Florida, stretches across four counties and reaches as far north as Brooksville.Freight trains run on those tracks now. But they could, one day, form the spine of a passenger rail system that would finally connect Tampa Bay — and ease the region's dependence on roads.This is no pie-in-the-sky scenario. It's an idea gaining sudden momentum because railroad giant CSX Corp. is shopping around two segments of its Tampa Bay routes.There is precedent in Miami and Orlando for converting freight lines to commuter rail. And no, it's not light rail. It doesn't require building brand-new rail infrastructure on top of existing development.That doesn't mean commuter rail is any more feasible than light rail — or cheaper. But now, it's an option."There's no question in my mind that there's going to be a very serious conversation about it," said former Hillsborough County Commissioner Mark Sharpe, one of the bay area's most vocal transit advocates."It's there, it's underutilized, and it connects important points. It's very viable."• • •For three decades now, local leaders have batted about the idea of converting freight rail to a passenger service.The bay area once had a Tampa Bay Commuter Rail Authority that pushed the concept in the 1990s but struggled to drum up support or funding. The agency folded soon after.In this decade, the Greenlight Pinellas effort considered incorporating the CSX tracks into its plan, then settled on a separate light rail system.That plan was rejected by Pinellas voters last year. Hillsborough voters did the same to a 2010 referendum that also included light rail.Transit proponents have long coveted the tracks. But one question always stood in the way: Was CSX open to a deal?It is now. At last month's meeting of the Tampa Bay Transportation Management Area Leadership Group, a gathering of the region's transportation planners, CSX said it's willing to sell two lines.One of the rail lines offered by CSX is the "Clearwater line." It stretches from downtown St. Petersburg, climbs northwest through Pinellas County to downtown Clearwater, veers to Oldsmar, then runs east past Tampa International Airport and ends near downtown Tampa, in Ybor City.The second route is the "Brooksville line." It starts in Tampa, juts north from the first line, passes by USF, cuts through Land O'Lakes in Pasco County and finishes in central Hernando County, near Brooksville.Urged by local leaders, CSX analyzed its lines and found that those two routes carried minimal freight traffic and could be used for passenger rail."We will continue to explore win-win scenarios that would help provide transportation alternatives to the citizens of Tampa Bay," said CSX spokeswoman Kristin Seay, "while allowing CSX to continue to meet the freight needs of its customers in the region."• • •It's unclear how much the lines would cost.SunRail, a freight-turned-commuter rail service that started running last year in the Orlando region, offers some cost comparisons.In 2011, CSX sold 61.5-miles of track to the Florida Department of Transportation for $150 million. That's $2.4 million a mile.Other costs bumped the project's total to $432 million. Federal money paid half the tab. The rest was split by the state and SunRail's local partners: the city of Orlando and four counties.Under the agreement, the state owns the tracks, which it leases to CSX for freight use. Otherwise, those rail lines carry passenger cars.Commuter rail is not light rail, however. Light rail is smaller and nimbler. It can make tight turns on city streets. It's electrified, either with an overhead wire or through the tracks.Commuter rail uses bulkier diesel-powered cars that run on the existing track. They're heavier so they can comply with federal crash regulations. Commuter rail is cheaper to build but carries heftier operating fees.Like light rail, stations have to be built. Unlike light rail, railroad crossings are already in place."People talk about rail here like it's one thing," said Ray Chiaramonte, executive director of the seven-county Tampa Bay Area Regional Transportation Authority, or TBARTA. "There's all different kinds. Some can go places others can't."• • •SunRail marked its first anniversary in April by carrying a million passengers, according to the Orlando Sentinel. In March, it averaged 4,100 paying customers a day, just below its target of 4,300. The 31.5-mile line is planning to double in size.It's had problems, though. SunRail doesn't reach Orlando International Airport, nor does it run often enough or on weekends, riders told the Orlando Sentinel.A Tampa Bay commuter system also would have drawbacks. The lines CSX offers don't connect the area's nexus: Tampa's Westshore area to St. Petersburg's Gateway area. They ignore the southeast (Brandon) and northeast parts of Hillsborough (New Tampa) and eastern part of Pasco (Wesley Chapel), where new housing has risen.But CSX's two Tampa Bay routes are a better fit for commuter service than the tracks in Orlando, say local officials.The Tampa Bay lines run through what Sharpe calls "key primary points" — the three major downtowns, Tampa International Airport and USF. Then, it stretches north toward the new bedroom communities in Pasco and Hernando counties."We would have better ridership than SunRail," said Beth Alden, the Hillsborough Metropolitan Planning Organization's executive director. "It's a real opportunity that we have as our opportunities seem to get narrower and narrower."• • •To seriously consider the idea, Tampa Bay's fractured municipalities would need to come together.SunRail is run by a regional government agency. Its board is comprised of elected officials from the region. The only comparable agency in this area is Tampa Bay Water, the regional water authority.TBARTA is the area's transportation planning agency, but the Legislature never gave it the power to tax and spend. Without money, it has little power.CSX will only sell its railroads to the DOT, which would work with local municipalities to build a governing and operating agency.Some fret that another transit option — commuter rail — will further muddy an already complicated transportation discussion. Nor will it help pay to fix the bay area's most pressing transportation need: a better bus service."I think we come out with these big ideas and try to do multiple things at once," Chiaramonte said. "We keep switching from one thing to another. We're just spinning our wheels."Meanwhile, the area's latest transit initiative, Go Hillsborough, isn't even on the 2016 ballot yet but now faces legal and ethical questions — and an investigation meant to dispel doubts instead has political leaders in retreat.CSX's offer gives Tampa Bay a new option to consider. The state has shown that when it comes to commuter rail, it's willing to partner with local communities — and help pay the bill."DOT has sort of thrown down the gauntlet on this with us," Alden said. "They're willing to work with us, but they need us to be partners at the table."Times news researcher John Martin contributed to this report. Contact Caitlin Johnston at [email protected] or (813) 226-3401. Follow @cljohnst.