BOSTON (State House News Service) – The constellation of highway tunnels beneath Boston, some of which are more than half a century old, are in line for more than $15 million in repairs to plug leaks and patch up worn-down surfaces.

State transportation officials on Wednesday approved a $15.3 million contract with SPS New England Inc. for maintenance on a quartet of tunnels that together carry hundreds of thousands of motorists every week.

Those tunnels — the Thomas O’Neill Tunnel that carries Interstate 93 underneath downtown Boston, the Ted Williams Tunnel that ferries drivers along Interstate 90 east and west across the harbor, and the westbound Sumner and eastbound Callahan Tunnels linking Boston and East Boston — have “a wide variety of areas with deterioration,” Department of Transportation Director of Major Projects Michael O’Dowd told the agency’s board.

“This contract will provide an opportunity for us to continue to maintain and do any of the cracked ceiling, waterproofing leaks — any place that’s showing some sort of health deficiency, decline in the overall conditions, this contract will give us an opportunity to go ahead and make those repairs as needed at locations that are varied throughout the tunnel system,” O’Dowd said.

Workers will seal leaks in the tunnels to prevent water from seeping in, which in turn will help prevent patches of ice from developing during winter months and posing risks for drivers. Crews also plan to repair concrete, replace fireproofing in locations where it has deteriorated, replace manhole covers and drainage inlets, clean drains and more.

Most of the repairs will take place during nighttime hours when traffic is lighter and require temporary lane closures, O’Dowd said.

“This is really a wholesale opportunity for maintaining the condition of the tunnels in good operating condition and safe conditions,” he said.

MassDOT board members unanimously approved the contract, which also includes $2.3 million in contingencies and another $600,000 to cover miscellaneous costs such as traffic police.

The four tunnels vary in age between 19 years old and 88 years old. Both the Ted Williams Tunnel, which opened in 1995, and the Thomas O’Neill Tunnel, which opened in 2003, were part of the historic Big Dig project.

The other two tunnels predate that transformation of the city’s roadway infrastructure: the Callahan Tunnel opened in 1961, the year a young outfielder named Carl Yastrzemski played his first game for the Red Sox, while the Sumner Tunnel began welcoming drivers in 1934 during Franklin D. Roosevelt’s first term as president.

State officials are also in the early stages of an extensive, roughly $160 million repair project for the Sumner Tunnel, prompted by a state of “disrepair” in the first-ever traffic tunnel to open in Massachusetts.

MassDOT is approaching the halfway point of that effort’s first phase, which involves closing the tunnel for a total of 36 weekends for maintenance. Next year, the tunnel will close for four continuous months for the second phase of the project, followed by another series of weekend-only closures in late 2023.

Highway Administrator Jonathan Gulliver said last month that after some initial traffic hiccups, the Sumner project is “going very well” with drivers mostly “settled in” to the required detours and changed travel patterns.