TITLE 23 , CHAPTER 1 , SUBCHAPTER I , Sec. 109.

U.S. Code

The Secretary shall not, as a condition precedent to his approval under section 106 of this title, require any State to acquire title to, or control of, any marginal land along the proposed highway in addition to that reasonably necessary for road surfaces, median strips, bikeways, gutters, ditches, and side slopes, and of sufficient width to provide service roads for adjacent property to permit safe access at controlled locations in order to expedite traffic, promote safety, and minimize roadside parking.

http://www4.law.cornell.edu/uscode/23/109.html