travel by vs travel

travel by is not a noun while travel is a noun.

Word	Noun	Adjective	Verb	Adverb
travel by	No	No	Yes	No
travel	Yes	No	Yes	No

As verbs, travel is a hypernym of travel by; that is, travel is a word with a broader meaning than travel by:

Other hypernyms of travel by include go, locomote, move.

travel by (noun)	travel (noun)
	the act of going from one place to another
	self-propelled movement
	a movement through space that changes the location of something

travel by (verb)	travel (verb)
move past	change location; move, travel, or proceed, also metaphorically
	make a trip for pleasure
	travel upon or across
	undergo transportation as in a vehicle
	undertake a journey or trip
	travel from place to place, as for the purpose of finding work, preaching, or acting as a judge