The MBTA commuter rail is losing roughly $35 million a year on fare evaders scoring free or cheaper rides, transit officials disclosed today as they rolled out a range of proposals to tighten up the system.

Roughly 15 to 20 percent of commuter rail riders aren't paying the correct fare, meaning one in five are either underpaying or not paying at all.

The $35 million estimate comes after officials at Keolis, which has operated the commuter rail since 2014, said it conducted a first-of-its-kind study to examine the system’s “long-standing” problem of riders either not paying or using sometimes elaborate ways to not pay full price on trains.

To address the issues, officials say they’re weighing a plan to spend $10 million to install gates and other infrastructure at North Station, South Station and Back Bay to create a “ring of steel” at the system’s primary stations.

The plan, which would take as many as 15 months to complete, would help recoup about $24 million a year, officials estimate.

T officials say the commuter rail is currently projected to bring in roughly $215 million in revenue this year and as much as $234 million next fiscal year after a range of fare increases go into effect.

MBTA officials also say they’re considering changes on the Green Line, where the system is losing as much as $4.5 million in lost fares as some riders board above-ground-trains in rear doors without paying.

The T is considering a pilot program to use private contractors over a two- to three-month span to actively check tickets, though it would likely require a “discussion” with the T Union, officials said.

Developing …