Signages on roads

Why are most of the road signs advising drivers on safety issues across the highway in English? Firstly Hindi is our national language, secondly bulk of the traffic on these roads comprises of truckers who would have limited knowledge of the langauge.. Someone pls explain..

The road signs on the national Expressway 1 between Vadodra and Ahmedabad had some very interesting ones. After trying to instill the rules for safety in the drivers they put up signages which say " Expressway - One Big Joyride".