In the fight over the Greenlight Pinellas transit referendum, the light-rail piece of the plan has drawn the most ire.

Critics say the 24-mile line in one area of Pinellas County would be a boondoggle and few would use it. Proponents call it the spine of a transportation network that would transform the county.

Still have questions ahead of Election Day? Here are some answers.

Why is light rail part of the plan?

Planners sought community input and considered more than a dozen modes of transportation as they conducted a required study to be eligible for federal grant dollars to develop mass transit. They chose light rail to serve as the spine of a system enhanced by a 65 percent increase in bus service.

Light rail moves people quickly on a dedicated corridor apart from traffic. Need more capacity? Add more cars to the train.

Proponents also say the line would boost the county's economy by spurring pedestrian-friendly development (and redevelopment) along the route. They point to light-rail systems in cities such as Charlotte, N.C., Denver and Minneapolis, where the economic impact has been measured in the billions of dollars, according to studies by the Center for Transit Oriented Development.

How do we know people would use it?

Slated to open in 2024, the light-rail line is projected to attract at least 17,000 trips per day by 2035, an estimate that Pinellas Suncoast Transit Authority officials say is conservative. The system would connect three major employment centers: Clearwater, St. Petersburg and the Gateway area, which together boast about 110,000 employees.

There is reason for skepticism, said David Hartgen, a transportation consultant and professor emeritus at the University of North Carolina.

"Most light-rail proposals connect jobs and residences, not jobs and jobs," Hartgen said, noting that 110,000 jobs is very low compared with other systems. "This means that the base of ridership is just not there."

Workers aren't the only riders who would use the system, said Heather Sobush, a senior planner for the PSTA. With an average of five residents per acre living within a half mile of the route, Pinellas has a residential density higher than St. Louis, Charlotte, Denver, Dallas and other cities that have successful light-rail projects, Sobush said. She said overall ridership would increase as development blossoms along the route and the line is extended.

How would we pay for it?

The light-rail line would account for $1.7 billion of Greenlight's total capital cost of $2.2 billion. It would cost about $30 million per year to operate.

The plan calls for about 37 percent of the rail construction to be funded by federal grants, about 13 percent by the state and the rest from the penny sales tax on the Nov. 4 ballot. Pinellas' sales tax would increase to 8 cents on the dollar, but PSTA's property tax would go away. Interest on construction bonds would add about $200 million to the cost.

The PSTA would be competing with other cities for federal "New Starts" grant money. The Federal Transit Administration rates projects using a formula that includes projected ridership, which the PSTA contends would grow as bus service expands in the early years of Greenlight.

The formula also takes into account whether a project has a stable funding source, which Greenlight would provide, and buy-in from local governments. Officials in St. Petersburg, Clearwater, Largo and the county have expressed support for the project.

Cassandra Borchers, the PSTA's chief development officer, said every community that has passed a referendum like Greenlight has received federal grant money.

How does light rail work?

Nearly all current light-rail lines in the United States are powered by overhead electric cables, but wireless technology is already available and will be more advanced in a decade, Borchers said. Trains would run every 10 to 15 minutes at speeds of up to 55 mph along existing roads. In stretches between Gateway and St. Petersburg, the trains would run alongside or in the median of I-275. The corridor for two trains — one in each direction — must be at least 30 feet wide. Travel time between St. Petersburg and Clearwater would be about an hour.

Would new train crossings back up car traffic?

Opponents have raised fears of traffic jams at train crossings, but those are unfounded, PSTA officials say. The planned route includes about 40 signal crossings. In many cases, the train would cross with vehicle traffic, so no extra signal cycles would be needed. In other cases, the train would add no more than 30 seconds to the cycle, Borchers said.

Are there plans to expand light rail to north and south Pinellas? What about Tampa?

There are no specific plans to extend the line to points north of Clearwater and south of downtown St. Petersburg. But planners say that's a strong possibility in future stages. According to the American Public Transportation Association, 27 of 28 regions in the United States that have built light-rail systems have extended them or are in the process of doing so.

The Tampa connection wouldn't happen until Pinellas and Hillsborough pass transit plans. Hillsborough's could be on the ballot as early as 2016. Both counties then could seek state and federal funding to build a line across Tampa Bay.

Contact Tony Marrero at tmarrero@tampabay.com or (727) 893-8779. Follow @tmarrerotimes.