Não informado. (1968). Research Results Digest. National Cooperative Highway Research Program.
Chicago-viite (17. p.)Não informado. Research Results Digest. Washington: National Cooperative Highway Research Program, 1968.
MLA-viite (8. p.)Não informado. Research Results Digest. National Cooperative Highway Research Program, 1968.
Varoitus: Nämä viitteet eivät aina ole täysin luotettavia.