just like most local traffic should not need to use an interstate highway. one might even be able to say that if you need to use an interstate, your commute is not really local anymore. actually, i think one could even argue that if a significant amount of local traffic goes over an interstate then the street system is designed wrong (although i admit, i fear that this is quite common). it's like letting a local commuter train use a high-speed rail track. it happens, but it shouldn't.