Lunt Flag Stop (Site)
GPS Coordinates: 38.7981471, -77.1353699
Closest Address: 5630 South Van Dorn Street, Alexandria, VA 22310

These coordinates mark the exact spot where the flag stop was located. No visible remains exist. The photograph above is an exact replica of what this flag stop looked like, with the standard Pennsylvania Railroad shelter directly abutting the railroad tracks.
A railroad flag stop is a station where a train will only stop if a passenger waiting on the platform waves a flag or gives a signal to the conductor, essentially requesting the train to stop; this is typically used at lightly used stations where trains wouldn't normally stop unless someone needed to get on or off. Many stations would have a box on the platform or station containing a white or green flag that the passenger would wave at the train. If it was a staffed station, the agent or clerk would flag the train. The conductor of the train would acknowledge they had seen the flag by sounding two short whistles.
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Here follows an excerpt from "The Iron Road of Franconia" book about the railroad written by local historian Nathaniel Lee.
LUNT FLAG STOP: 1890-1953
This railroad line through Fairfax County changed its name several times, which continues to be the cause of much confusion for armchair historians. The Richmond, Fredericksburg and Potomac Railroad Company was chartered in 1834, and the line was finished as far as Fredericksburg by 1837. From this point, passengers bound for Washington took a coach to Aquia Creek and then took a steamboat up the river. The line then extended to join the Pennsylvania Railroad's subsidiary line, the Alexandria and Washington Railroad after the Civil War. In 1872, the name was changed to the Alexandria and Fredericksburg Railroad Company. In 1890, the Washington Southern Railway took control of the railroad through Fairfax County, and then folded into the Richmond - Washington Company as a part of the RF&P Railroad in 1920, which is what most people remember. CSX Transportation finally took over operations along the line in 1991. Confused yet? You should be. That's about six name changes over 150 years for the railroad in Fairfax County. Please read the book "The Iron Road of Franconia" for a more detailed explanation of all the changes.
Moving ahead to 1890, the Lunt flag stop opened on the Old Lincolnia Road, Samuel H. Lunt (1846-1925) started out working as a pharmacist in Alexandria with his father and brother before branching into real estate speculation at the turn of the twentieth century. The photograph below shows the family home downtown at 631 King Street. The Lunt waiting shelter was located on the south side of the tracks roughly 200 feet west of South Van Dorn Street, located on what is today a used car lot.
Samuel Lunt arranged many of the land transactions and condemnations throughout the Alexandria area for the railroad. He also purchased several large parcels of land west of what is today Van Dorn Street in the hopes that he could develop a new town there. When he lobbied for a flag stop to serve property he wanted to develop, the railroad company was happy to oblige. The station platform remained in place until 1960 even though Samuel's grand "town center" plans never came to fruition. The station was finally doomed by construction plans for the new Capital Beltway, which necessitated the destruction of the old platform.