The MBTA is holding a public meeting on plans for a new parking garage and other improvements at the Salem commuter rail station at 6:30 p.m. Tuesday at the Carlton School, 10 Skerry St. Officials will give an update on the project, which is now at the 30 percent design stage. The estimated $39.9 million project calls for construction of a five-level, 710-space parking garage, along with new train platforms, an attached enclosed platform waiting area, and two elevators, according to the MBTA. The plan also provides for a bus platform, taxi lane, and drop-off/pickup area. The garage will include space for charging stations for electric vehicles and for Zipcars, motorcycles, and bicycles. A covered pedestrian bridge will connect Bridge Street to the elevators and stairs down to the train platform.