Tkd a02

The Guidelines for Road Design 374 Appendix 9.A - Interchanges Figure 9-A-1 Four-leg Interchanges between Expressways 375 The Guidelines for Road Design Figure 9-A-2 Three-leg Interchanges between Expressways The Guidelines for Road Design 376 Figure 9-A-3 Simple Diamond Interchange Advantages * high standard single exits in advance of the structure * high standard single entrances beyond the structure * economical in property use and construction costs * where the expressway is depressed, the grades of the ramps assist the deceleration of exiting traffic and the acceleration of entering traffic * single exit feature simplifies signing of expressway * no need for speed change lanes on or under the structure * no weaving on the expressway Disadvantages * lower capacity on the minor road due to left turning movements * difficulty of obtaining adequate visibility at the open throat ramp terminals especially where the minor road crosses over the expressway * many points of conflict on the minor road increase the accident potential of the design, unless signalized * possibility of wrong-way movements * turning traffic from the expressway is obliged to stop at the minor road, 377 The Guidelines for Road Design storage lane treatment may be required * little possibility of allowing for future expansion of the interchange but increased volumes may be handled by: (a) channelizing the open throats (b) installing signals on the minor road (three phase), or (c) providing two-lane left turns The Guidelines for Road Design 378 Figure 9-A-4: Split Diamond Interchanges Advantages * high standard single exits and entrances * economical in property use and construction costs * where the expressway is depressed, the grades of the ramps assist the deceleration of exiting traffic and the acceleration of entering traffic * single exit feature simplifies signing of expressway * no need for speed change lanes on or under the structures * no weaving on the expressway * increased capacity over the other forms of diamond interchanges Disadvantages 379 * additional structure required * possibility of wrong-way movements * stop on minor road for left turn The Guidelines for Road Design 380 The Guidelines for Road Design 381 The Guidelines for Road Design 382 The Guidelines for Road Design Figure 9-A-7: Parclo A-B, Trumpet and Rotary Interchanges 383 The Guidelines for Road Design