Residents have an opportunity to learn more about the MBTA’s plans for a new parking garage and other improvements at the Salem commuter rail station. The transit agency is holding a public meeting on the project from 6:30 to 8:30 p.m. Thursday at the Carlton School, 10 Skerry St. The meeting will include an introduction of the project team, an update, and a discussion of potential effects. The estimated $31 million project is now in preliminary design. It calls for construction of a 553-car parking garage, with about 150 spaces set aside for the new J. Michael Ruane Judicial Center on Bridge Street. The number of spaces in the garage has been reduced from a planned 800 because of budget limits, says MBTA spokeswoman Lydia Rivera.