I pity anyone who uses the Maryland MTA site to plan their trip and who doesn't know about things NOT in the MTA system. For instance, here's the map I was shown when I went to double check times for Cromwell Station to BWI Amtrak: a one hour trip via the 17 bus:
Thing is, there's a shuttle from the airport - which has a light rail stop right next to it - to the Amtrak station. Trip is about 25 minutes, more like 10 if you're lucky connecting. But it's not an MTA shuttle, it's an airport shuttle, so it doesn't feature in their trip planner:
They did point out it was only 12 minutes by cab...