Abstract—Accident investigation (AI) aim to answer what, how, why, when of accident happens. Moreover, we need to know what can be done to prevent a reoccurrence and what can be done to minimize accident consequences. Thirteen serious accidents were in-depth investigated by an expert team. Almost accident factors were human errors which occurred in daytime. Human errors are doze off, lack of driving experience, speeding and suddenly brake and lane changing of passenger drivers and pickup drivers. Accident causes by vehicle defects are related with wheel system such as exploding of tire and malfunction of braking system. Severity level could be reduced by fasten seatbelt, lower speed, non-illegal parking, truck protection system, reinstall and redesign of guardrail, crash cushion providing and budget allocation. We suggest engineering, education and law enforcement to minimize accident consequences.