How to play: drag from one point to another to place a beam - the magnifier above your finger shows exactly where it will land, and points snap to existing joints. Blue squares are fixed anchors on the cliffs.
Pinch to zoom and drag with two fingers to pan. Quick deck lays a road across for you, and Quick truss adds steel supports underneath; change them however you like, or erase beams to save money.
Only Road beams carry the car; Steel is stronger but the car drives through it, so use it for bracing. Triangles are strong, rectangles wobble.
Desktop: mouse wheel zooms, Shift+drag pans, right-click or Esc cancels, keys 1/2/3 pick tools, Space tests, Ctrl+Z undoes.