There's a reason I bring up the Washington DOT every time I give a presentation about using social media in public works. They were early on the scene to realize how much social media could assist them in public relations, and they've done a great job figuring out how best to engage the public. And just when I thought they couldn't possibly get any cooler, they come up with an innovative bridge building initative to help people understand and take part in the process.
The way it seems to work is that as pontoons for the actual bridge are constructed, the Washington DOT posts materials people can use to construct their own representative pontoons. They also have videos showing the transport of the actual pontoons to the jobsite. The activity offers the public an interesting and interactive way to better understand the bridge and what is actually taking place on the jobsite. Here's the description of how it works from their site along with a photo of one of the templates that can be used to construct a pontoon.
"As we complete the construction of each pontoon and bring them to Lake Washington, we will post new templates here. Each pontoon is individually named according to its location within the final bridge structure. Simply print, cut along the indicated lines and then fold your pontoon for final construction."