Boulder is taking another step toward construction of its proposed public broadband fiber network, even as the cost keeps increasing.

The city next week will hold a public hearing on the financing behind the planned building of 55 miles of “dark fiber” broadband backbone — the infrastructure is described as dark at this stage because it won’t be used to transmit data for commercial purposes until the city or a future partner begins operating the system, according to a Boulder news release.

The latest total cost estimate of the dark fiber skeleton, or the sections of the network most crucial to its potential future buildout, has been estimated at $20 million, a city news release stated, up significantly from the $11 million approximate price tag put before council in April 2018 as officials considered how involved Boulder should be in operating the system once complete.

That was followed by a $15 million estimate presented to respondents of a city survey published in June 2018 that showed overwhelming support to build the fiber backbone. More than half of respondents to the survey also said they would be willing to vote for a sales tax hike to support the city broadband project.

City council in April approved $2.5 million for additional investment in fiber laterals extending from the backbone.

“This brings us closer to what the community asked for in the survey which is a municipally-led internet service provider, which had a much more expensive cost associated,” said Bryan Rachal, the city’s deputy director of communications. “So we believe this in line with the goals of both council and the community.”

If approved, the backbone would require underground construction work in, and across the city in 2020 and 2021, the release said.

If you go

What: Public hearing on Boulder broadband backbone

When: 7 p.m., Aug. 6

Where: Municipal Building, 1777 Broadway, Boulder

Cost: Free

More info: bouldercolorado.gov/city-council/community-broadband