Walter McClure and Ben Lamp were both researchers with the Department of Agricultural Engineering at The Ohio State University. In the late 1950s, they conducted a 10-year retrospective study of fatal tractor accidents and the impact of slow moving vehicles in these fatalities. Ken Harkness, also from Ohio State’s Department of Agricultural Engineering, built on that research and led a team that developed the Slow Moving Vehicle symbol in 1962.
The symbol with its distinctive orange triangle bordered in red is still used today and is backed by the Occupational Safety and Health Administration and the American National Standards Institute. In 1992 the American Society of Agricultural Engineers (ASAE) designated the development of the symbol as an ASAE Historic Landmark.