The state highways herein provided for shall be paved with granite, asphalt, or wood blocks, bricks, concrete, bituminous concrete, sheet asphalt or other pavement having a hard surface and of a durable character, but nothing in this chapter shall prevent the commissioner from maintaining roads heretofore improved with other materials or with their present or similar surfaces pending their paving with materials complying with this chapter.

In all cases the width of the pavement shall be at least eighteen feet and the total width of the roadway shall be at least thirty feet, except at bridges, culverts, or grade crossings, where the roadway shall be of such width or widths as the commissioner may deem necessary and determine.

All sharp turns and angles and railroad grade crossings shall be eliminated wherever practicable.