The cost of building MARTA’s first major transit line in a generation has risen tens of millions of dollars, and construction will be delayed, the agency said Thursday.

MARTA previously estimated it would cost $61.5 million to build the Summerhill bus rapid transit line in Atlanta. Now it says the work will cost $91.3 million — an increase of nearly 49%.

Construction was originally set to begin this month, with the line opening in August 2024. Now construction won’t begin until spring, and the project won’t be finished until July 2025. And MARTA will eliminate two proposed stations on the line to help save money.

Agency officials said costs have risen in part because the project will require more work than expected, including replacing pavement along the route. Inflation that has plagued the construction industry also played a role.

Similar problems may affect other projects as MARTA prepares for major expansions in Atlanta and Clayton County.

“We’re, candidly, going to see this with other projects going forward,” Manjeet Ranu, chief of capital programs, told the MARTA board of directors Thursday. “The cost estimates are very low.”

The revelations are the latest sign that rising prices, supply-chain problems and labor shortages are affecting construction projects across Georgia. Last month the Georgia Department of Transportation rejected 12 highway construction bids and withdrew six more because of rising prices. GDOT said bids, on average, are 33% higher than expected.

The Summerhill line is MARTA’s first major transit line since construction of its rail system ended 22 years ago. It’s part of a $2.7 billion expansion plan made possible when Atlanta voters approved a half-penny transit sales tax in 2016.

The Summerhill line would run along Hank Aaron Drive/Capitol Avenue from the Atlanta Beltline to downtown Atlanta. It would operate mostly in exclusive bus lanes to keep passengers moving and include other features designed to mimic MARTA’s rail service.

On Thursday, Abhay Joshi, director of construction management, attributed the escalating costs and delays to a variety of factors.

Joshi told the board that geotechnical studies found MARTA would need to replace concrete in the bus lanes along the line — not simply repave them. He said pavement in the general-purpose lanes will also have to be replaced, though Atlanta will seek other revenue to pay for that work.

Other costs also came in higher than expected. That includes the cost of painting the bus lanes red to distinguish them from regular lanes. In an interview, Joshi said the cost of the paint itself and the cost of the labor to paint the lanes was significantly higher than expected.

The costs of right of way, utility relocation and professional services also will cost millions more than originally expected.

MARTA and Atlanta have agreed to numerous changes to reduce costs. They will eliminate planned stations on Memorial Drive at Capitol Avenue and Trinity Avenue. Among other things, MARTA will also postpone plans to use solar power for lights, cameras and other electronics at stations.

Joshi said the latest schedule includes activities that originally were not accounted for, including training for bus drivers and federally required safety certification.

Board member Stacy Blakley expressed concern about the dramatic cost and schedule changes.

“To me, it feels like we’re starting to normalize overspending,” she said. “We’re pretty much asking for $30 million.”

Other board members attributed the problem to MARTA’s recent lack of experience building new transit lines.

“When I got here a decade ago, we were spending a bunch of money in the capital program maintaining what we have, but we weren’t building anything,” board member Robbie Ashe said. “As we continue to start building things, I want to make sure we do it as efficiently as possible.”

Ranu told the board MARTA is taking steps to improve its cost and schedule estimates going forward. It’s adding staff to handle the expansion work and has hired a consultant to examine its estimates.

MARTA has several other expansion projects under way in Atlanta. It recently approved plans for bus rapid transit along Campbellton Road, and it’s studying transit and route options for its proposed Clifton Corridor line to the Emory University area.

The agency also has plans for bus rapid transit lines in Clayton County.