I got a response about two months ago to an earlier Infosnack article, "Delays involving single tracking", which discussed whether Metro should be turning trains around just short of a single-track section during a major service disruption. Here's what Metro's Rail Operations Control Center Director Hercules Ballard had to say:
We regret that you and other customers experienced lengthy delays on February 19, 2009. In routing trains during a derailment or other serious service disruption, the Operations Control Center (OCC) has to consider many factors, including the number of available trains, the time required to turn trains around, the time of day, the location of the derailment, and the number of customers who would be helped or hindered.
On February 19, 2009, some trains were turned around at the Ballston Metrorail station as you suggested; as circumstances quickly changed, other trains were turned around at East Falls Church Metrorail station, and still others were not turned back. Turning back trains at Ballston Metrorail station allowed us to reduce the inconvenience to customers travelling toward New Carrollton. It also meant we were sending fewer trains into the single-tracking area, thereby reducing platform wait times for Vienna-bound customers.
Obviously from inside a Metrorail train it's hard to tell to what extent this idea is possible or being used, but it's good to know what they take into account and that they use it during disruptions.
A PARP request for the incident report for these disruptions did not turn up documents that were terribly interesting. The full report had not been finalized and was not released to me because it was considered "pre-decisional".