The GCIE Handbooks make reference to a number of International Standards:

International Organisation for Standards

ISO 2145: Documentation — Numbering of divisions and subdivisions in written documents

ISO 3832: Passenger cars — Luggage compartments — Method of measuring reference volume

ISO 4130: Road vehicles — Three-dimensional reference system and fiducial marks — Definitions

SAE International

SAE J826: Devices for Use in Defining and Measuring Vehicle Seating Accommodation

SAE J941: Motor Vehicle Drivers’ Eye Locations

SAE J1052: Motor Vehicle Driver and Passenger Head Position

SAE J1100: Motor Vehicle Dimensions (the GCIE Handbook Part 3 is harmonised with this document)

United Nations Economic Commission for Europe

UN-R125: Forward field of vision of the motor vehicle driver (link to pdf version here)

US Government

40 CFR 600.315-08: Classes of comparable automobiles