.29 cD, car the size of a US compact, small diesel, about 108 miles per US gallon, sounds plausible to me, it would probably get an "EPA" score better than a TDi golf. Could probably get close to the same in a VW Lupo diesel with heavy hypermiling.
The route looks like it might have been carefully picked for staying out of the hills, impose a topo map on it, and you'll probably find they go round them or up valleys.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice