This paper discusses coding of road information in a lateral reference system using magnetic markers designed for Automated Highway Systems ( AHS). The coding is utilized to communicate road information such as up- coming road geometry or lane merges/diverges from the roadway infrastructure to AHS vehicles. The work presented here is based on experiences with the preparation of the I-15 test track near San Diego, CA, for the National AHS Consortium demonstration in 1997. Information about road features was encoded into the magnets used as a lateral reference system for automatic steering control by exploiting binary polarity coding.