Perhaps someone might explain to me why in table 300.5, when using direct burial cables or conductors, we get a reduction in burial depth from 24" to 18" if the conductors are under a one or two family dwelling driveway versus ran through a lawn area of a one or two family dwelling. The reason this seems strange to me is that there is no NEC requirement that the residential parking area/driveway be concrete or asphalt. We could be talking a "designated" parking area/driveway that is nothing more than tire tracks in the dirt. 
Pete
Pete