If any discontinued highway shall be upon lands through which a new highway shall be laid out, the same may be taken into consideration in estimating the damages sustained by the owner of such lands; and in like manner the benefits accruing to owners of lands by reason of laying-out, altering, widening or otherwise improving any highway or of changing the line thereof, shall be taken into consideration in determining the damages to be paid to any such owner as compensation for the taking of any of his property for any such highway purpose. In each such case, the board or commissioner having the matter in charge, or the court commissioners, as the case may be, shall state such fact and the amount deducted on account thereof in the determination, or report, as the case may be: Provided, however, That benefits shall not be taken into consideration as above stated in case there is any assessment levied on the abutting property by reason of the laying out, altering, widening or otherwise improving said highway.