M22-01. 20 Design Manual
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- Điều hướng trang này:
- 1360.02(2)(a) Directional
- 1360.02(2)(b) Semi directional
- Chapter 1360 Interchanges WSDOT Design Manual M 22-01.20 Page 1360-3 September 2021
| 1360.02(2) Interchange Patterns
Basic interchange patterns have been established that can be used under certain general conditions and modified or combined to apply to many more. Consider alternatives in the design of a specific facility; however, the conditions in the area and on the highway involved govern the final design of the interchange. Selection of the final design is based on a study of projected traffic volumes, site conditions, geometric controls, criteria for intersecting legs and turning roadways, driver expectancy, consistent ramp patterns, continuity, and cost. The patterns most frequently used for interchange design are those commonly described as directional, semi directional, cloverleaf, partial cloverleaf, diamond, and single point (urban) interchange (see Exhibit 1360-1). 1360.02(2)(a) Directional A directional interchange is the most effective design for connection of intersecting freeways. The directional pattern has the advantage of reduced travel distance, increased speed of operation, and higher capacity. These designs eliminate weaving and have a further advantage over cloverleaf designs in avoiding the loss of sense of direction drivers experience in traveling a loop. This type of interchange is costly to construct, commonly using a four-level structure. 1360.02(2)(b) Semi directional A semi directional interchange has ramps that loop around the intersection of the highways. This results in multiple single-level structures and more area than the directional interchange. Chapter 1360 Interchanges WSDOT Design Manual M 22-01.20 Page 1360-3 September 2021 1360.02(2)(c) Cloverleaf The full cloverleaf interchange has four loop ramps for the left-turning traffic. Outer ramps provide for the right turns. A full cloverleaf is the minimum type interchange for a freeway-to-freeway interchange. Cloverleaf designs often incorporate a C-D road to minimize signing difficulties and remove weaving conflicts from the main roadway. The principal advantage of this design is the elimination of all left-turn conflicts with one single-level structure. Because all movements are merging movements, it is adaptable to any grade line arrangement. The cloverleaf has some major disadvantages. The left-turn movement has a circuitous route on the loop ramp, the speeds are low on the loop ramp, and there are weaving conflicts between the loop ramps. The cloverleaf also needs a large area. The weaving and the radius of the loop ramps are a capacity constraint on the left-turn movements. tải về 1.86 Mb. Chia sẻ với bạn bè của bạn:
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