The Washington State Department of Transportation wanted to figure out why construction projects often end up costing more than expected. They looked at 433 projects from 1985 to 1989 and found that bigger, more complex projects with lots of bidders tend to have more cost overruns. Projects like new construction, bridges, and safety improvements are especially prone to going over budget. So, to keep costs down, it's important to carefully plan and manage these types of projects.