Tampa Bay's most traveled bridge needs to be replaced.

The original Howard Frankland Bridge opened in 1960 and a new southbound span was finished in 1991. Now the original span has reached the end of its lifespan and a new bridge must be built in the next decade.

Here's how the Florida Department of Transportation plans to do that. (Spoiler alert: it involves toll lanes.)

Current bridge

The 1990s southband span, Tampa to St. Petersburg, four lanes.

The 1960 northbound span, St. Petersburg to Tampa, four lanes.

Here's the Howard Frankland as it currently stands. Drivers have four lanes in each direction.

A few years ago, local leaders had approved the state's plan for a new bridge that would include toll lanes. But what many of those leaders didn't know was that those toll lanes would replace existing lanes. So, drivers who didn't want to pay would lose a free lane.

Those willing to pay to get across the bridge — the price would change price based on traffic — could use the fourth lane.

The Tampa Bay Times first reported the lost free lane in September. More than a dozen elected officials told the Times they did not know that DOT's plan included reducing the number of free lanes.

The state then scrapped its plan in October, saying it wouldn't take away a free lane on the Howard Frankland.

READ THE FULL STORIES HERE: State's answer to Howard Frankland traffic: Pay a toll or lose a lane

DOT reverses course, says it won't take free Howard Frankland lane

In January, state officials unveiled a new plan for the Howard Frankland bridge.

A new, six-lane bridge will be built to the north of the existing bridges. It will carry traffic south, from Tampa to St. Petersburg. Two of those lanes will be tolled (one in each direction). A concrete barrier will separate them from each other and regular traffic.

New bridge

Steve Madden

Steve Madden

The direction of traffic on the 1990s span would switch, and start flowing from St. Petersburg north to Tampa. It will still have four free lanes.

The current northbound span (the original 1960 structure) will then be torn down.

The state plans to start construction in 2020, and expects the entire process, including tearing down the old bridge, to take about five years.

Because both bridges will be open while DOT builds the new span to the north, officials expect the impact on traffic to be minimal.

This is all part of Tampa Bay Next, the state's $6 billion plan to add 90 miles of toll lanes to the bay area's interstates.

Contact Caitlin Johnston at cjohnston@tampabay.com or (727) 893-8779. Follow @cljohnst.