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Dyfyniad Arddull ChicagoNational Research Council (U.S.). Transportation Research Board. Meeting. Roadside Safety and Other General Design Issues. Washington, D.C: National Academy Press, 1999.
Dyfyniad MLANational Research Council (U.S.). Transportation Research Board. Meeting. Roadside Safety and Other General Design Issues. National Academy Press, 1999.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.