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Some noteworthy AASHTO publications are: [9] A Policy on Geometric Design of Highways and Streets, often called "The Green Book" because of the color of its cover. This book covers the functional design of roads and highways including such things as the layout of intersections, horizontal curves, and vertical curves.
The primary US guidance is found in A Policy on Geometric Design of Highways and Streets published by the American Association of State Highway and Transportation Officials (AASHTO). [2] Other standards include the Australian Guide to Road Design Archived 2011-11-09 at the Wayback Machine, and the British Design Manual for Roads.
Minimum number of lanes: There are to be at least two lanes in each direction, unless more are necessary for an acceptable level of service, according to the current edition of AASHTO's A Policy on Geometric Design of Highways and Streets. Climbing lanes and emergency escape ramps should be provided where appropriate.
The following section pertains to only North American highway LOS standards as in the Highway Capacity Manual (HCM) and AASHTO Geometric Design of Highways and Streets ("Green Book"), using letters A through F, with A being the best and F being the worst, similar to academic grading. A: free flow. Traffic flows at or above the posted speed ...
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The highest design speed for a road or segment is the design speed of its least favorable part. For example, given a road segment with a 60 miles per hour (97 km/h) design speed except for a curve with a 45 miles per hour (72 km/h) design speed, the entire segment would have a 45 miles per hour (72 km/h) design speed.
Highway engineering (also known as roadway engineering and street engineering) is a professional engineering discipline branching from the civil engineering subdiscipline of transportation engineering that involves the planning, design, construction, operation, and maintenance of roads, highways, streets, bridges, and tunnels to ensure safe and effective transportation of people and goods.
The route numbers and locations are coordinated by the American Association of State Highway and Transportation Officials (AASHTO). [4] The only federal involvement in AASHTO is a nonvoting seat for the United States Department of Transportation. Generally, most north-to-south highways are odd-numbered, with the lowest numbers in the east and ...