In 1941 it look Southern's #17 15 minutes to transit from WAS to ALX.
http://www.streamlinerschedules.com/concourse/track1/birmspecial194112.html
Nowadays the same trip takes 18 minutes.
http://www.amtrak.com/ccurl/427/412/Northeast-Regional-3-Schedule-040615.pdf
I'm being somewhat glib however. Someone taking today's 171 would get into Charlottesville 30 minutes faster, and Lynchburg 1 hr faster, than Southern's 17. (Same depature times interestingly even after 70+ years).
Take note, for example, of the fact that Southern's 17 took 15 minutes WAS-ALX...NB, however, 18 has 20 minutes allocated.
Part of this is differing equipment (that train was probably still heavyweight in 1941...and I'm pretty certain it was still a steam loco at the time, too), part of it differing stopping patterns.
One thing to rememebr is that 171, leaving WAS, has to contend with a ton of VRE trains at that time...and said trains stop at L'Enfant Plaza and Crystal City (I believe that 171 also stops at L'Enfant Plaza, though that isn't listed on Amtrak's timetables). Of course, on some of the longer hauls the inverse is also true (witness, for example, the Southern Crescent's schedule in 1971...or, more impressively, the Piedmont LImited's schedule...vs. Amtrak's current schedule and note all the extra stops).
As to the similar schedules...all I''m going to say is that the guy who picked that schedule is a very astute student of history (I've seen him discuss all sorts of nuances of historical railroad policy in great depth) and he notably switched the proposed schedules around at the last minute...that similarity is very likely
not an accident.
Edit: Just confirmed the VRE hypothesis. VRE 307 leaves WAS at 1640 and arrives into ALX at 1703 (the 23 minutes are down to L'Enfant and Crystal City both being passenger heavy...I've seen
Amtrak trains lose five minutes because you'll have a hundred people looking to board, and that's before VRE enters the equation). Amtrak's departure is stuck with that train's schedule to contend with.