( They ( also ( ( work ( to ( ( ( reduce congestion ) and ) ( ( improve ( air quality ) ) ( by ( dropping ( ( the amount ) ( of ( cars ( on ( the road ) ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (NP (PRP They)) (ADVP (RB also)) (VP (VBP work) (S (VP (TO to) (VP (VP (VB reduce) (NP (NN congestion))) (CC and) (VP (VB improve) (NP (NN air) (NN quality)) (PP (IN by) (S (VP (VBG dropping) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NNS cars)) (PP (IN on) (NP (DT the) (NN road)))))))))))))) (. .)))
They also work to reduce congestion and improve air quality by dropping the amount of cars on the road.
(ROOT (S (S (VP (VBG Limiting) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS cars)) (PP (IN on) (NP (DT the) (NNS roads)))))))) (VP (MD would) (ADVP (RBS most) (RB likely)) (VP (VB improve) (NP (DT the) (NN air) (NN quality)) (PP (IN in) (NP (JJ large) (NNS texas) (NNS cities))))) (. .)))