Dead south on US 15.
Get on the interstate below Marysburg before taking US 15 south straight through.
You will pass Gettysburg PA, cross into Maryland towards Frederick then have a choice of routes towards richmond.
IF you are a 48 foot trailer (NOT A 53 ... or ... 65 foot overall length or shorter Stay on 15 into Virginia crossing just west of DC, cross over US 50 through Manassas, Find US 17 near Opal run east until I-95 at Freeericksburg VA 133mile marker, take 95 south.
Washington is in chaos, so bypass it entirely on US 15.
Scales at US 15 x US 50 near Manassas. Maybe open maybe not.
DO NOT stop anywhere in Manassas because the local Judge hates truckers has for years. Falls back on your overall length at 65 feet long for combination vehicle tractor and trailer oR a 48 foot trailer or two pups etc.
Mind your overhang. IF a 48 foot, set that rear axle tires about 4 feet inboard from the ICC bumper if you can do it by weight.
IF you get hungry there is a fast food stop at Opal US 15 at or near US 17. But a Fredericksburg Truckstop series at I-95 from roughly 133B mile marker straight to richmond.
FAST? Well if its 2 am, go on. Get going yer late.
IF its rush hour? Forget it. You will get down here eventually.
DO not use 81 to get out of PA. You cross into a little bit of WVA too far west and have to recross to get back over to Richmond in the mountains. Not worth the fuel burn.
These are general ideas and I usually run that route. Doublecheck on the trailer restrictions on US 15 in Virignia first. IF you are overlength say with a big sleeper tracto