Calling on Nashvillians to get behind the most sweeping and expensive project in Metro history, Mayor Megan Barry on Tuesday unveiled a $5.2 billion mass transit proposal that sets up a monumental decision for the city.

Barry wants Nashville voters to go to the polls in May to approve a referendum on increases to four taxes to pay for the massive undertaking — a combination of 26 miles of new light rail, more robust bus service, and a major tunnel below downtown where the new transit lines would run.

The main revenue generator would be a one-half percent hike to Nashville’s sales tax in July 2018 that would jump to 1 percent in 2023. She also proposed increases to the city’s hotel-motel tax, rental car tax and business and excise tax.

Read more:

►How the $5.2 billion proposed transit system would be funded

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►See the map of the proposed transit plan

After months of behind-the-scenes work — and years of transit planning to tackle the region's increasing traffic congestion — Barry presented the legacy-defining and likely controversial plan to city leaders and Metro Council members at Music City Center on Tuesday morning.

Three former Nashville mayors — Karl Dean, Bill Purcell and Phil Bredesen — were among those on hand.

‘It will serve every part of our city’

Barry, speaking before an overflow room of primarily transit bootsers, said more transportation options will improve Nashville’s quality of life and make the city a better place for generations by giving “transportation independence” to more Nashvillians.

“It will be far-reaching, it will serve every part of our city — north, south, east, and west — and it will help to shape our future growth and development,” Barry said.

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“And it will not be free,” she said. “It will be an investment in our future, and I believe Nashvillians will be willing to make the investment when they learn more about this proposal and how it will change the way they live.”

Dubbed “Let’s Move Nashville: Metro's Transportation Solution," the entire project has a timeline of 15 years, with improvements to existing Metro Transit Authority bus services on tap in 2019. But the first light rail line would not open until 2026.

Light rail proposed for five corridors

The city would build light rail with dedicated lanes first on Gallatin Pike in 2026, and then on Nolensville Pike, Murfreesboro Pike, and Charlotte Avenue. The plan also calls for a Northwest Corridor line that would run on existing railroad lines — from Charlotte Avenue near 20th Avenue to North Nashville toward Bordeaux — passing by Tennessee State and Fisk universities. In addition, a light rail connection would extend to the Nashville International Airport. The targeted completion date for the light rail system is 2032.

Downtown tunnel to cost $900 million

A 1.8-mile, three-stop tunnel under downtown — first reported by The Tennessean last week — would stretch from Music City Central, the city’s bus hub on Charlotte Avenue, north-south under Fifth Avenue South to Lafayette Street, where an additional hub would be built.

Early on in design work for the light rail plan, project leaders deemed a tunnel under downtown necessary because of downtown’s congestion and narrow streets. Building on downtown streets would have also presented complicated right-of-way acquisitions.

“That’s where Nashville’s downtown underground will come into play,” Barry said.

Under the tunnel plan, there would be an access station for passengers at Lower Broadway. The tunnel, which by itself would cost around $900 million, would be used for both light rail and new electric buses. The tunnel wouldn’t be complete until 2027 under the project's timeline.

Barry touts quick improvement to buses

In addition to the long-term rail project, Barry touted an assortments of short-term improvements to existing MTA bus service, including the move to new electric buses, additional crosstown routes, 15-minute peak service on busy routes and more frequent bus service that would run 20 hours out of the day.

Rapid bus transit also planned

The city has proposed 25 miles of new rapid bus lines for Dickerson Pike, Hillsboro Road, West End Avenue and Clarksville Pike in Bordeaux. Unlike light rail, this type of transit would use limited curbside bus lanes instead of dedicated lanes and has more frequent service, enhanced traffic signals, and improvements to bus stops such as level-platform boarding.

Neighborhood transit centers to provide access

Around two-dozen “neighborhood transit centers” would be built on locations along both the light rail and rapid bus lines. They also include the new downtown light rail hubs at Music City Central and Lafayette Street. Phased in over a five-year period, these hubs would offer access to the transit system and feature park-and-ride areas, bike facilities and sidewalks.

Project gets more expensive than expected

Much of Barry’s plan is detailed in nMotion, a 25-year transit plan adopted by the Metro Transit Authority and Regional Transportation Authority last year.

But while nMotion outlined a $5.97 billion for the entire multi-county Middle Tennessee region, Barry’s plan is nearly as much, $5.2 billion, just for Davidson County. Project leaders say the cost grew because of more detailed engineering work and the downtown tunnel, which was not part of the nMotion plan.

Although some observers had seen underground transit as a non-starter because of Nashville’s hard limestone geology, the mayor’s office says it can be done with new drilling technology. Seattle and Pittsburgh are among the cities that have done similar drilling to what the city is proposing.

Free, reduced service proposed for the poor

In an attempt to assuage fears that the poor will disproportionately shoulder the sales tax increase, Barry has proposed reducing — and in some cases eliminating — bus and transit fares for Nashville residents who live at or below the federal poverty line.

For Barry, the transit endeavor is supposed to deliver on a core campaign promise — “Transit, transit, transit,” she said Tuesday are her three priorities.

It also comes amid a period of major, overlapping projects for the mayor as she seeks council approval of a $275 million Major League Soccer stadium.

► More:Mayor Barry unveils financing proposal for Major League Soccer stadium in Nashville

Barry’s administration plans to submit legislation to the council in December for approval to add the transit tax proposal referendum to the May 1 local primary ballot.

Reviews came in strong Tuesday from those who have called for mass transit, while Barry’s proposal did nothing to change attitudes of critics.

Vice Mayor David Briley endorsed the plan Tuesday as he introduced the mayor at Tuesday’s event, calling it an “incredibly bold” proposal that’s the only way Nashville can maintain its quality of life.

Competing reactions to Barry’s plan

“The safe thing would have been to do a little bit, frankly,” Briley said. “Leaders, like Mayor Barry, elect not to do the little things, the safe things, but to do the bold thing. And the bold thing here is to reflect all of the work this community has done over the last 10 years looking at transit.”

Councilman Freddie O’Connell, a longtime transit advocate, heaped similar praise, applauding the plan to reduce fares for the poor.

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“Frankly, I think this plan exceeds my expectations for what can work in Nashville,” he said. “Across the next 25 years, ultimately nobody is going to notice that $5 billion thing.”

Ralph Schulz, president and CEO of the Nashville Area Chamber of Commerce, said Barry presented “a bold plan that’s just the size for Nashville.”

But Ben Cunningham, president of the Nashville Tea Party, who has launched a petition effort that takes aim at the transit plan, said cities across the country are abandoning light rail and other “legacy transit system.”

He instead pointed to autonomous vehicles as the wave of the future for transit and touted on-demand car pooling through companies like Uber and Lyft

“Light rail and bus systems are being left behind by transit consumers,” he said. “It is obsolete now.”

Councilman Robert Swope, who has also touted autonomous vehicles, said Barry’s plan has a “lot of unanswered questions.”

“There’s a lot of discussion that needs to be had before I think anything should be presented to a public referendum,” he said. “It’s 200-year-old technology trying to solve a modern-day problem.”

Tax increases to cover costs

The four tax increases collectively are expected to generate around $110 million in annual revenue for transit beginning in 2019, ramping up to around $200 million by 2023.

► The sales tax hike would increase Nashville’s rate from 9.25 percent to 9.75 percent beginning July 2018 and to 10.25 percent in 2023. The mayor’s office is highlighting data suggesting 47 percent of sales tax collections are from out-of-county visitors. The new sales tax surcharge passed by the state in the spring allowed Nashville to go above the state’s current cap of 9.75.

► The mayor has proposed a quarter surcharge on the hotel-motel tax beginning next year. It would jump to three-eighths in 2023, pushing it to a rate to 6.375 percent overall – one of the highest in the nation.

► A 20 percent surcharge would be added to the local car rental tax that would move it from 1 percent to 1.2 percent.

► A 20 percent hike has been proposed for the city’s business and excise tax. For a business that currently pays $1,000 in taxes, the increase would mean an additional $200.

Barry: Design answers not all finished

Under the proposal, local taxes would sunset after 50 years.

The state’s approval in the spring of Gov. Bill Haslam’s IMPROVE Act gave the new transit referendum option to Nashville and other municipalities. In addition to the local taxes, Barry said the city plans to identify federal funding to help pay for the project.

Barry first started discussing her light rail proposal in April. But she said more questions will need to be addressed on design even after the referendum in May. The mayor’s office has organized a series of six meetings over the next two months to discuss the transit plan.

Ahead of the transit vote, a political action committee tied to the chamber of commerce, called Citizens for Greater Mobility, organized this summer. The group plans to raise millions from the business community to back the mayor’s proposal.

The PAC is assisting efforts of the Transit for Nashville Coalition, which has more than 60 member organizations and has garnered 10,000 petition signatures pledging support for transit expansion.

For years, transit advocates have pushed for a regional solution to address Middle Tennessee’s congestion. Although Barry’s plan involves only Nashville, the mayor said it “should not be seen as the finish line.”

“It should be seen as a starting point to connect with our regional neighbors.”

Reach Joey Garrison at 615-259-8236, jgarrison@tennessean.com and on Twitter @joeygarrison.