Flagging up National Speed Limit roads on routes

Since there are databases detailing the speeds of all roads, would it not make sense to highlight National Speed Limit roads (with no pavement) on the gpx route or point them out in the Route description itself, this would then help users to better be warned as they approach these areas and it would act as a better mitigating factor. It may give them an option to plan out an alternative route then if they wanted to avoid it completely.