Job "A" and job "B" are essentially the same, however Job B requires ~40% travel.
Job A makes 100K. How much would an applicant for Job B expect to make or could ask for in negotiations with the expected travel amount in mind?
Note that this applicant would rather not travel 40%, but is not opposed to some travel.

Travel by what means? Also travel time is counted different then reguler time so there will have to be agreements on what it is and how the law reads. See portal to portal act and other related federal laws.

Of course I am assuming that all travel costs are paid by the company. If the jobs are basically the same position, often you will not see any real difference in the salary for the position. Things like actual duties, not job title, also size of the company, how stable the company is, turn over in that position and more make more difference in salary offers