A method and apparatus for a navigation system evaluates an overall cost of each candidate route by incorporating traffic information such as traffic incident types and traffic flow speeds. An optimum route to the destination is determined by comparing the costs of two or more candidate routes and selecting a candidate route of the least cost. The method and apparatus determines relevancy and accuracy of the traffic information and adjusting the cost of the candidate route. When the traffic information on the candidate route shows a conflicting situation, the method and apparatus modifies the cost derived from the traffic information. When modifying the cost, the traffic speed information is prioritized over other type of traffic information.