I lived literally next to Dulles International Airport - ~8 miles. Yet, to get to Dulles (or Reston/Herndon) by Public transit, would've taken me 2 hours perhaps, or more.
Ha! I live in Reston and mapped out some options on Goole Maps...
Home to IAD by car: 5 miles, 9 minutes
Home to IAD by transit: 40+ minutes across 2 bus lines
Home to IAD by foot: 10.9 miles, 3+ hours
Home to WAS by car: 24 miles, 29 minutes
Home to WAS by transit: 90+ minutes across 1 bus line, 2 Metro lines, and a few walking segments to link them.
It's sad that walking to the airport is twice as far than driving. It's also sad that I can drive to a airport further away than I can access my closest airport by transit.
Fair enough, I always take a cab/Uber to IAD, as that cost is far less than the price of parking. And living so close to IAD, I try to fly out of it whenever possible (all work travel, 80% of pleasure travel).
Except (unless they've built new paths since I last checked) you can't realistically walk to the airport either. The only non-limited-access highway entrance is on the north side of the airport, so unless GP lives in Ashburn, you'll have to walk around the airport first (and if you're east, that means finding a decent crossing for Route 28...). Then you have such pedestrian friendly places as this[1].
I lived literally next to Dulles International Airport - ~8 miles. Yet, to get to Dulles (or Reston/Herndon) by Public transit, would've taken me 2 hours perhaps, or more.