Capital Metro has estimated its proposed $9.6 billion transit plan would cost the average Austin homeowner about $300 a year.

The proposed 9- to 10-cent bump to the city of Austin’s property tax rate would increase the city tax rate by between 21% and 22.5%, a considerable jump that would trigger a tax rate rollback election under state law.

Transit authority and city staff delivered the estimate at a joint meeting of the Austin City Council and Cap Metro’s board Monday. The plan includes building an underground light rail system with stations downtown, a high frequency rail line along Guadalupe Street and Lamar Boulevard and a rail route to Austin-Bergstrom International Airport.

State law requires taxing entities to hold elections when they propose increasing property tax revenue by more than 3.5%. Local officials are targeting November to place the question before voters.

While nothing is set in stone, Monday’s presentation was the first glimpse into how transit and city officials are considering to finance what proponents see as a once-in-a-generation investment.

"The age of the Band-Aid approach to transportation has to be long gone," Sen. Kirk Watson, D-Austin, said at a rally Monday at City Hall. "We need to think big and the folks who have their sleeves rolled up working, tackling this complex issue, they need to keep thinking big too."

Large infrastructure projects in Austin are generally financed through bond elections, which call for voter approval before taking on often hundreds of millions of dollars in debt to be paid back over decades through property tax revenue.

However, state law prohibits funding maintenance through tax-financed debt, and finding a dedicated source for the proposed rail lines’ upkeep is a key component needed to access federal money that could finance 40% of the system’s construction.

A tax rate election "is a viable option," said Greg Canally, Austin's deputy chief financial officer. "It meets all the criteria we are talking about and it gets it done in one vote."

The Federal Transit Authority could pay for $3.8 billion of the system, Cap Metro estimates. Getting that cash generally requires having a dedicated funding source — which a tax increase would indicate, officials said.

"We have to commit that if all else fails, this is the path (forward)," Council Member Alison Alter said. "This is how we commit."

The last tax rate election held in Austin was a 2012 referendum to increase Central Health’s tax rate by 5 cents. It was approved with about 55% of voters in favor.

However, the last time Austin held a transit election was in 2014; that proposal, for a $600 million rail line, failed.

Cap Metro projected that it would take nine years to complete the Orange and Blue lines — light rail lines going down the spine of Central Austin and from downtown to the airport, respectively — including five years of construction that could bring underground light rail stations to Republic Square and Auditorium Shores.

The Gold Line, a bus rapid transit route from Cap Metro’s downtown station to Austin Community College’s Highland Campus, would also be completed nine years after securing funding, but with only three years of construction.

Other parts of the plan include expanding MetroRapid bus service, improvements to the already existing Red Line commuter rail and creation of a second commuter rail line from downtown to Colony Park and as far as Elgin.

Staff will conduct several public engagement events in the coming months to discuss the details of the project. Meanwhile, Cap Metro and city staff will finalize their revenue model in April. The council and the transit authority’s board will hold another joint meeting in May.