M22-01. 20 Design Manual
tải về 1.86 Mb. Chế độ xem pdf
|
- Điều hướng trang này:
- 1360.06 Interchanges on Two-Lane Highways
| Chapter 1360
Interchanges WSDOT Design Manual M 22-01.20 Page 1360-22 September 2021 1360.05 Ramp Terminal Intersections at Crossroads Design ramp terminal intersections at grade with crossroads as intersections at grade (see Chapter 1300). Whenever possible, design ramp terminals to discourage wrong-way movements. Locate ramp terminal intersections at grade with crossroads to provide signal progression if the intersection becomes signalized in the future. Provide intersection sight distance as described in Chapter 1310 or Chapter 1320. 1360.06 Interchanges on Two-Lane Highways Occasionally, the first stage of a conventional interchange will be built with only one direction of the main roadway and operated as a two-lane two-way roadway until the ultimate roadway is constructed. The design of interchanges on two-lane two-way highways may vary considerably from traditional concepts due to the following conditions: • The potential for cross-centerline crashes due to merge conflicts or motorist confusion. • The potential for wrong-way or U-turn movements. • Future construction considerations. • Traffic type and volume. • The proximity to multilane highway sections that might influence a driver’s impression that these roads are also multilane. Provide the deceleration taper for all interchange exit ramps on two-lane highways. Design the entering connection with either the normal acceleration taper or a “button hook” configuration with a stop condition before entering the main line. Consider the following items: • Design the stop condition connection in accordance with a tee (T) intersection as shown in Chapter 1310. Use this type of connection when an acceleration lane is not possible. Provide decision sight distance as described in Chapter 1260. • Since designs may vary from project to project, analyze each project for the most efficient signing placement, such as one-way, two-way, no passing, do not enter, directional arrows, guideposts, and traffic buttons. • Prohibit passing through the interchange area on two-lane highways by means of signing, pavement marking, or a combination of both. The desirable treatment is a 4 foot median island, highlighted with raised pavement markers and diagonal stripes. When using a 4-foot median system, extend the island 500 feet beyond any merging ramp traffic acceleration taper. The width for the median can be provided by reducing each shoulder 2 feet through the interchange (see Exhibit 1360-28). • Include signing and pavement markings to inform both the entering and through motorists of the two- lane two-way characteristic of the main line. • Use as much of the ultimate roadway as possible. Where this is not possible, leave the area for future lanes and roadway ungraded. • Design and construct temporary ramps as if they were permanent unless second-stage construction is planned to rapidly follow the first stage. Design the connection to meet the needs of the traffic. tải về 1.86 Mb. Chia sẻ với bạn bè của bạn:
|