Columns of vehicles are grouped in travel zones alternating with empty zones , and are laid out in {HEAD ~ a centrally controlled grid pattern} of {TAIL ~ fastroads}  
of
Columns of vehicles are grouped in travel zones alternating with empty zones , and are laid out in { HEAD ~ a centrally controlled grid pattern } of { TAIL ~ fastroads }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH