Start by laying out your road deck. In 4-9, you will likely notice the deck wants to sag in the middle.
Use wood for the majority of the support structure and save steel only for the highest-stress joints. poly bridge 4-9
If your road is still sagging, look to the skies. Start by laying out your road deck
This is the most popular community solution. It involves building a support structure that swings the road sections to the right as the vehicle moves. While this often leads to the structure breaking after the car passes, it is a valid way to clear the level if the vehicle reaches the flags. If your road is still sagging, look to the skies
If you're looking for help or a solution for level 4-9 in Poly Bridge, here are some general tips that might be useful:
The Art of the Upward Arc: A Comprehensive Guide to Poly Bridge Level 4-9