THE STATE HIGHWAY administrator said the traffic mitigation costs associated with the repairs of the Sumner Tunnel will be borne by the Department of Transportation, the MBTA, and the Massachusetts Port Authority.

Jonathan Gulliver, the administrator, said it hasn’t been decided yet how the costs will be split among the three agencies.

Chanda Smart, a member of the MBTA board of directos, asked about the payment arrangement during a briefing on the repair project Thursday. Neither Smart nor other members of the MBTA board asked any other questions.  A Jamaica Plain resident raised concerns about the arrangement during the public comment period.

When the mitigation efforts were first announced on June 9, state transportation officials were silent on who would pay and subsequently said the issue was being debated internally.

Transportation advocates have applauded the mitigation measures, but questioned why the MBTA is being forced to spend money to help alleviate traffic problems associated with a highway project. The Sumner Tunnel is shutting down for nearly two months starting July 5 to repair the ceiling of the tunnel and will shut down next year for another two months to repair the roadway section of the tunnel.

The T during this initial shutdown is allowing riders to use the Blue Line for free.  Ferry service between East Boston’s Lewis Mall and Long Wharf will also be free. Commuter rail riders from as far north as Salem and Swampscott will see their fares drop from $8.75 to $2.40 and discounts will be available to those using the Tobin Bridge, the Ted Williams Tunnel, and Logan Express buses. Drivers parking at T garages will also pay reduced amounts.

No estimate has been released on the cost of the mitigation measures.