If you're looking for a meeting place or a good stop around ½ or halfway between Arlington, VA and Philadelphia, you can try Aberdeen, MD, which is a little over 1 hour northeast of Arlington, VA, or a little over 1 hour southwest of Philadelphia.
About ¼ or a fourth of the way, you can stop at Baltimore, MD. This is about half an hour northeast of Arlington, VA.
About ⅓ or a third of the way, you can stop at Towson, MD. This is almost an hour northeast of Arlington, VA.
About ⅔ or two thirds of the way, you can stop at Newark, DE. This is about 1½ hours northeast of Arlington, VA, or almost an hour southwest of Philadelphia.
About ¾ or three fourths of the way, you can stop at Wilmington, DE. This is about 2 hours northeast of Arlington, VA, or about half an hour southwest of Philadelphia.
If you drive straight through without stopping at all, the total distance is 145 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 2 hours, 31 minutes.