The second phase of U.S. Bank Stadium's enhanced security perimeter could be bigger and more expensive than initially planned and taxpayers will be asked to pay for it, the Minnesota Sports Facilities Authority (MSFA) chair said Thursday.

Until now, the cost estimate was about $48 million. But Chair Michael Vekich said Kansas City, Mo.-based architectural firm Populous will develop a better estimate in coming weeks.

The enhanced perimeter is intended to keep fans of the Minnesota Vikings and concert-goers safe from a possible attack when they're inside. At the monthly MSFA meeting Thursday, commissioners signed off on a $374,000 contract with Populous to develop designs for the next phase.

Vekich expects Populous to provide two or three design options for the next phase in November when, he said, "We'll have a better idea what the legislative ask is."

Whatever they decide on design, Vekich said the MSFA will be asking Gov. Tim Walz and the Legislature for money in 2024, either in cash from the state's treasury or in state bonding money.

One main question of the second phase is whether to extend the perimeter across Chicago Avenue S., which is closed to vehicle traffic on event days.

Once complete, the perimeter will lift the stadium's security level to K12 under Department of State anti-terrorism threat levels. The standard means the perimeter can stop a 15,000-pound vehicle traveling at 50 miles per hour, protecting the more than 60,000 fans inside during Vikings games.

The second phase perimeter spending will be on top of $15.7 million approved by the Legislature in 2023 for the first phase currently under construction by Minneapolis-based J.E. Dunn and expected to be complete after the Minnesota Vikings' current season.

During the first phase, a permanent 8-foot black fence that can't be climbed is replacing the temporary gray chain-link that has been used for years.

In addition, the first phase includes cables, gates, crash-prevention bollards and in-ground wedge barriers that stop vehicles from entering.

The building's most prominent entrance on the western face with the plaza and the pivoting glass doors will be fortified in the second phase.

Vekich said the new perimeter won't close off the building to the public.

The $1.1 billion stadium was constructed with a combination of private and public money and opened in August 2016. In June, the state paid off its share of the debt using the cash that had accrued from electronic pull-tab revenues. The initial plan was to pay it off in 2046.

Under the 2012 legislation to build the stadium, the state covered $348 million and Minneapolis was to pay $150 million with the Vikings' owners paying the rest.

But the costs for the building don't end with the retirement of the debt. The Vikings have said the building must be kept at a first-rate level. A study conducted for the MSFA determined the building will need $280 million in maintenance in the coming decade, including the $48 million for the next phase of the perimeter.