I make the commute from Baltimore to DC every day, and I absolutely agree. The Northeast Regional averages about ~90 mph between Baltimore and Wilmington. If it did the same from Baltimore to DC, it'd be a sub-30 minute trip. The only reason it can't is the lack of capacity through tunnels in Baltimore, tunnels into DC, and at DC Union Station. Heck, the biggest bottleneck is probably the single escalator in Union Station leading down from the MARC/Amtrak concourse to the Metro station.