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Questions and Answers About Vehicle Size and Weight

23 CFR 658.9 National Network Criteria

23 CFR 658.9 National Network Criteria

Must traffic lanes on the National Network be 12 feet wide?

Although a traffic lane on the National Network (NN) is required to be designed to have a width of 12 feet or more, lesser widths may be allowable if otherwise consistent with highway safety. 23 CFR 658.9(b)(5)

As an example, design standards for highways on the NN that are also part of the NHS, can be found in 23 CFR 625. On the NHS, design exceptions must be prepared when required lane widths cannot be obtained. In addition, 23 U.S.C. 109(b) requires that roadways are designed with standards to accommodate the types and volumes of anticipated traffic. There are several tools and methodologies that can be applied to determine the safety and operational impacts of design decisions which include the Highway Safety Manual (HSM), the Highway Capacity Manual (HCM), and performance-based practical design.
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