HARRISBURG — The Pennsylvania Department of Transportation on Friday announced it will privatize 558 bridges, selecting a partnership’s $899 million proposal to replace and maintain the spans.

The highway department announced its choice of Plenary Walsh Keystone Partners for the project, which calls for construction to be finished in three years, followed by maintenance over the following 25 years.

Borrowing costs are expected to bring the total cost to $1.8 billion over the 28-year life of the deal.

Bridges were selected based on whether they had a similar, relatively simple structure and required full replacement, as well as those that were structurally deficient, more than 50 years old or ready to be built soon.

Bundling the projects together reduced the average cost per bridge to about $1.6 million, compared with $2 million under a standard approach.

Work is scheduled to begin next summer, and 58 bridges are expected to be completed during 2015.

The state will still own the structures and perform some basic maintenance, such as removal of snow or vegetation.

Pennsylvania’s more than 25,000 bridges include more than 4,000 that are structurally deficient.

Plenary Walsh Keystone Partners is comprised of The Walsh Group, Granite Construction Co., HDR Engineering, HNTB Corp. and Infrastructure Corporation of America.