. ▁ ▁The ▁draw back s ▁are ▁that ▁they ▁are ▁heavily ▁poll uting ▁and ▁rely ▁on ▁limited ▁natural ▁resources . ▁ ▁There ▁are ▁many ▁propos als ▁to ▁har ness ▁renew able ▁forms ▁of ▁energy , ▁to ▁use ▁foss il ▁fuel ▁more ▁efficiently , ▁or ▁to ▁use ▁human ▁power , ▁or ▁some ▁hy brid ▁of ▁these , ▁to ▁move ▁people ▁and ▁things . ▁ ▁The ▁list ▁below ▁contains ▁some ▁forms ▁of ▁transport ▁not ▁in ▁general ▁use , ▁but ▁considered ▁as ▁possibilities ▁in ▁the ▁future . ▁ ▁Air - prop elled ▁train ▁( ab andon ed ▁in ▁ 1 9 th ▁century ) ▁B ounce ▁t ube ▁p neum atic ▁travel ▁( Pro posed ▁by ▁Robert ▁A . ▁Hein lein ▁in ▁ 1 9 5 6 ) ▁V act rain ▁also ▁known ▁as ▁E T 3 ▁Bi Modal ▁G lide way ▁( D ual ▁Mode ▁Transport ation ▁System ) ▁travel ▁( Pro posed ▁by ▁William ▁D . ▁Davis , ▁Jr . ▁in ▁ 1 9 6 7 ) ▁TE V ▁Project ▁( pro posed ▁by ▁Will ▁Jones ▁in ▁Summer ▁ 2 0 1 2 ) ▁K wik ▁Lane ▁also ▁sp elled ▁as ▁Q wik ▁Lane ▁( pro posed ▁by ▁McC r ary ▁Personal ▁Transport ▁Systems , ▁L LC ▁in ▁ 2 0 1 1 ) ▁D ual - mode ▁vehicle ▁ ▁Hyper loop ▁Int ellig ent ▁Transport ation ▁System ▁Jet ▁pack ▁Back pack ▁hel ic opter ▁La unch ▁loop ▁Or b ital ▁ring ▁Personal ▁air ▁vehicle ▁( F lying ▁car ) ▁Personal ▁rapid ▁trans it