Adding 2 extra beams to your bridge will increase the weight capacity by 60%. This is prefect for high traffic bridges of long bridges that will have a lot of people on them at one time.

2 Extra Beam Counts:
  27" wide - 4 beams (Standard is 2 beams)
  36" wide - 5 beams (Standard is 3 beams)
  48" wide - 5 beams (Standard is 3 beams)
  60" wide - 6 beams (Standard is 4 beams)
  72" wide - 7 beams (Standard is 5 beams)