Making an arch bridge for a school project is easily accomplished using a recycled medium flat-rate U.S. Post Office shipping box and a few other supplies you probably already have around the house. A single arched bridge created in this scale can display small toy cars for a realistic bridge effect. Making an arch bridge is a fun project for a student to undertake, and the project can be finished in a weekend.
Use a ruler to measure 9 inches down from one of the 11 7/8-inches wide sealed box ends. Draw a line around this point on the box, and cut the excess away.
Use the 3¼-inch diameter circle as a pattern to create your arch. Measure 4 inches down from the top centre of the circle and draw a line horizontally across the circle. Cut along this line, forming a half-circle with a flat bottom edge.
Lay the box flat on the table and centre the arch pattern (half-circle) on the box, aligning the flat bottom edge of the arch pattern with the bottom cut edge of the altered priority shipping box. Trace around the circle, creating the outline of an arch. Trace the same pattern on the other flat side of the box, making sure the arches line up as best as possible on each side of the box. Cut the half-circles from the box.
Stand the box so the cut edge is touching the table, the arch beneath the "road" of the bridge, which is the sealed box end.
Glue toothpicks, vertically, with the glue gun, every inch across the outside edges of the sealed end of the box. The toothpicks are forming the bridge railing posts. The last "post" will be slightly longer than an inch from the previous one to align it with the edge of the box end. Repeat for the other side of the box, forming a 3...-inch "road" between the two lines of toothpick "posts."
Cut one craft stick in half with the scissors. Glue 2½ craft sticks horizontally, with the glue gun, one at a time, on the outside of the toothpicks to form the bridge railing. Align the straight side of each craft stick with the tops of the toothpicks. It will look like a fence with the wider craft sticks glued on the exterior of the toothpicks/posts. Repeat for the other external side of the bridge railings.
Paint the entire bridge, railings, ends, sides and arches brown with the acrylic paint. Allow paint to dry.
Paint the road (3...-inch width by 11...-inch length), which is the sealed, painted box end, black. Allow paint to dry.
Paint a yellow stripe down the centre of the road. Allow paint to dry.
Glue one or two die-cast toy cars onto the road on the arch bridge for a realistic touch.