Also don't forget to program in specific sites unless you have GPS on. Cecil, Harford, Anne Arundel are the sites I will usually toggle on as I head South. Unfortunately the FIRST system doesn't seem to cover the beltway yet. The PG Simulcast rarely has traffic. The Anne Arundel Simulcast has surprising range. I'll hear MSP units from all over (Golden Ring, JFK, BelAir, Glen Burnie, Annapolis, Centerville, etc.) on that site and I can hear it all over AACO..
I'm not the expert on MSP but that's my current strategy. If I want to monitor beltway, you have to hit Montgomery County or Prince Georges County systems.