The Collaborative International Dictionary of English v.0.48:

Turnpike \Turn"pike`\, v. t. [imp. & p. p. Turnpiked; p. pr. &
   vb. n. Turnpiking.]
   To form, as a road, in the manner of a turnpike road; to
   throw into a rounded form, as the path of a road. --Knowles.
   [1913 Webster]