Started by Haljackey, November 26, 2011, 01:00:51 PM
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Quote"A very simple design involving two carriageways, usually perpendicular to each other however other angles are perfectly possible, of different grade (grade being quantity of traffic usually handled). The major grade carriageway in a diamond is referred to as the surface road, as it is customary that the road with higher usage has the least deviation from the horizontal. The minor grade carriageway is reflected to in this case as the street. The street may go either over or under the surface road but it will clearly undergo a greater elevation change if both routes intersect on level ground.Diamonds are the simplest 4 ramp interchanges. They are often used in where there is a very large grade difference in the carriageways such as highways passing through inner boroughs of cities. However they scale up badly. At the ramp/street intersection, unless the street is very low grade, there must be lights. This slows down traffic, and if the street is high grade, cause congestion. Furthermore if the majority of traffic is using only one ramp of the interchange then efficient light timings are going to cause congestion on the street, especially if it is cross-carriageway turning (a left turn in the US or a right in the UK)."
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