Section 131-B. County highways and bridges

1. A board of supervisors may,
  when satisfied that it is for the  interest  of  the  county,  lay  out,
  construct, open, alter or discontinue a county highway therein, or cause
  the  same  to  be done, and construct, repair or abandon a county bridge
  therein, or cause the same to be done when the board shall deem that the
  interest of the  county  will  be  promoted  thereby.  All  expenses  so
  incurred  shall  be a county charge, and may be financed pursuant to the
  local finance law.
    2. Whenever the board of supervisors of a county  shall  determine  to
  construct  a  bridge in accordance with the foregoing provisions of this
  section, such board, on behalf of the county, and the town  board  of  a
  town  or  in  case  of a city the board of aldermen or any similar board
  exercising the functions of aldermen, on behalf of such  town  or  city,
  may  enter  into  an  agreement with the county, to the effect that such
  town or city will operate and maintain such bridge, in case  the  bridge
  is  located  wholly in a town or city. In case the bridge is constructed
  over a stream forming the boundary line between two towns or two  cities
  or  between  a  town  and  city,  then they may agree with the county to
  operate and maintain such bridge jointly, in proportion to the  assessed
  valuation of such town or city. The sum which the town or towns, city or
  cities  are obliged to pay under such an agreement is a charge upon such
  towns or cities and shall be paid as other  town  or  city  charges  are
  paid.