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AASHTO 01 Chapter III Instructor: Dr. Nedal Ratrout

Design Considerations. The maximum superelevation may be different of different highway conditions. At the other extreme, no e is needed for tangent highways or highways with extremely long-radius curves.. Design Considerations. Maximum Superelevation Rates:The maximum rates of e used on highways

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AASHTO 01 Chapter III Instructor: Dr. Nedal Ratrout

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    1. AASHTO ’01 Chapter III Instructor: Dr. Nedal Ratrout

    2. Design Considerations The maximum superelevation may be different of different highway conditions. At the other extreme, no e is needed for tangent highways or highways with extremely long-radius curves.

    3. Design Considerations Maximum Superelevation Rates: The maximum rates of e used on highways are controlled by four factors: Climate conditions. Terrain conditions. Type of area. Frequency of very slow-moving. Using only one maximum e rate within region of similar climate and land use is desirable, as such a practice promotes design consistence. The highest e rate for highways in common use is 10 percent, although 12 percent is used in some cases.

    4. Design Considerations 8 percent is recognized as reasonable maximum value for e rate. In summary, it is recommended that several rates, rather than a single rate, of maximum e should be recognized. A rate of 12 percent should not be exceeded. A rate of 4 or 6 percent is applicable for urban design. Superelevation may be omitted on low-speed urban streets.

    5. Design Considerations Minimum Radius: The minimum radius of curvature is also an important control value for determination of superelevation rates for flatter curves. Exhibit 3-13, exhibit 3-14 gives the minimum radius for each of the five maximum e rates for design speeds form 20 to 130km/h [15 to 80 mph].

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