| The department may alter, widen or change the grade of any |
state or state aid highway whenever in its judgment the public |
exigency may require, and may lay out, establish and open a |
new highway as a state highway, and upon appropriate petition |
from municipal officers may lay out, establish and open a new |
highway as a state aid highway. It may discontinue a highway, |
or a portion thereof, as a state or state aid highway and the |
same shall must be thereafter maintained by the town or county |
originally liable therefor except as otherwise provided. All |
costs of the construction, maintenance and repair of state or |
state aid highways are the responsibility of the department |
and may not be passed on to a local unit of government except |
with the agreement of the legislative body of that local unit. |