CSX milepost prefixes
Most CSX railroad lines are given lettered prefixes before milepost numbers. These prefixes are one to three letters long with the first letter usually refer to the former company. For instance, prefixes beginning with "S" were part of the Seaboard Air Line Railroad. Some of these company prefixes include the following:
- Former Atlantic Coast Line Railroad lines begin with "A"
- Former Baltimore and Ohio Railroad (B&O) lines begin with "B"
- Former Conrail (Penn Central) lines begin with "Q"
- Former Chesapeake and Ohio Railway (C&O) lines begin with "C"
- Former Clinchfield Railroad lines begin with "Z"
- Former Georgia Railroad lines begin with "Y"
- Former Louisville and Nashville Railroad lines begin with "0" (zero)
- Former Pittsburgh and Lake Erie Railroad lines are designated "PLE", "PLY", and "PLM"
- Former Richmond, Fredericksburg and Potomac Railroad lines are designated "CFP" (on the former main) and "CFQ" (Dahlgren Branch)
- Former Seaboard Air Line Railroad lines begin with "S"
Atlantic Coast Line Railroad
Lines that were formerly part of the Atlantic Coast Line Railroad system are given milepost prefixes beginning with the letter A. For instance, milepost A790 is on the main line in Orlando, Florida, 1000 miles south of the beginning in Richmond, Virginia, and milepost AN587 is in Waycross, Georgia, 587 miles south of Richmond on the branch to Montgomery, Alabama (which splits near milepost 548 in Jesup). Three-letter prefixes are used for minor branches of these branches, or minor branches off the mainline - for instance ANA is the northernmost branch of AN.
Before the ACL merged into the Seaboard Coast Line Railroad in 1967, none of the prefixes had the initial "A". The letters "I" and "Q" were skipped, and double-lettered prefixes (like KK, which would be AKK post-1967) were not used.
A is given to the main line from Richmond, Virginia to Port of Tampa, Florida. It has been pieced together from many sections of original main lines and newer connections; the full line is still in use by CSX.
- Richmond and Petersburg Railroad, Manchester, Virginia to Petersburg, Virginia (A23)
- Petersburg Railroad, Petersburg to Weldon, North Carolina (A85)
- Wilmington and Weldon Railroad, Weldon to Wilson, North Carolina (A139)
- Wilson and Fayetteville Railroad, Wilson to North Carolina/South Carolina state line (A255)
- Florence Railroad, state line to Pee Dee, South Carolina (A283)
- Wilmington and Manchester Railroad, Pee Dee to Florence, South Carolina (A293)
- Northeastern Railroad, Florence to Charleston, South Carolina (A388)
- Ashley River Railroad, around Charleston (A388-392)
- Charleston and Savannah Railroad, Charleston to Savannah, Georgia (A491)
- Atlantic and Gulf Railroad, Savannah to Jesup, Georgia (A548)
- Folkston Cutoff, Jesup to Folkston, Georgia (A602)
- Waycross and Florida Railroad, Folkston to Georgia/Florida state line (A606)
- East Florida Railroad, state line to Jacksonville, Florida (A643)
- Jacksonville, Tampa and Key West Railway, Jacksonville to Sanford, Florida (A766)
- South Florida Railroad, Sanford to Tampa, Florida (A890)
AA is the northernmost spur, running from A89/AA89 at Halifax, North Carolina southeast and south to AA178 in Kinston, North Carolina. It was all built as the Scotland Neck Branch of the Wilmington and Weldon Railroad.