The MBTA’s plan to construct a parking garage and make other improvements at the Salem commuter rail station will be the subject of a public meeting Wednesday, at 6:30 p.m. at the Carlton School, 10 Skerry St. MBTA officials will offer an update on the project, which is now at the 90 percent design stage. The estimated $39.9 million project calls for a five-level, 700-space parking garage with new train platforms, an enclosed platform waiting area, and two elevators. A bus platform, a taxi lane, and a drop-off/pick-up area are also included. A covered pedestrian bridge will connect Bridge Street to the elevators and stairs down to the train platform. There will be upgrades to lighting, signs, and landscaping.