America's Byways: By the United States Federal Highway Administration. Shows the location of and details about each routing

Highways Agency: Official site. Includes an interactive roadmap providing information on roadworks and expected delays

Historic Route 66: Detailed maps and directions for following the "mother road", plus news and information

I69Info.com: Overview and link collection

Kurumi's Field Guide to Interchanges: Descriptions and diagrams of many types

Manual on Uniform Traffic Control Devices: The standard for signs, signals, and pavement markings in the United States. Includes HTML and .pdf versions

National Traffic and Road Closure Information: Links to the respective pages in all U.S. states' department of transportation websites

NYCroads.com: Guide to the expressway, parkway, bridge and tunnel network in the New York-New Jersey-Connecticut metropolitan area. Exit listings for area highways. County route logs for several area counties

Pennsylvania Turnpike: Official site by the Turnpike Commission. Includes toll rates

Society for All British Road Enthusiasts: Includes route logs, history, photographs, links, and international discussion