If you have a hard deadline and are taking metro, check their website a day or so before and see if there is any planned track maintenance that will be causing delays that weekend.
To reach Lorton and the Auto Train by 2pm on a Sunday, I'd probably allow 60-90 minutes if driving from the Tidal Basin. Using Metro, I'd allow a hour from the Smithsonian stop to Franconia-Springfield (40 minutes train time plus potential wait time for the train) plus another half hour or so driving to Lorton. So imo it's a wash time wise and comes down to personal preference.
To reach Lorton and the Auto Train by 2pm on a Sunday, I'd probably allow 60-90 minutes if driving from the Tidal Basin. Using Metro, I'd allow a hour from the Smithsonian stop to Franconia-Springfield (40 minutes train time plus potential wait time for the train) plus another half hour or so driving to Lorton. So imo it's a wash time wise and comes down to personal preference.
