<polyline id="beampath"  stroke="brown" stroke-width="4" fill="transparent">
   <animate id="bridgeLeft" attributeName="points" dur="1s"
   begin = "0s; bridgeLeft.end + 2.5s "
    from="20,62 30,62 35,62  50,62 "
      to="20,62 30,62 35,70  45,88"
      fill = "freeze"
    />
   </polyline>