C4 Cases of misphasing fall into four types These are described below together

C4 cases of misphasing fall into four types these are

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chainage. C.4 Cases of misphasing fall into four types. These are described below together with the necessary corrective action for each type. Insufficient separation between the curves. C.5 If there is insufficient separation between the ends of the horizontal and vertical curves, a false reverse curve may appear on the outside edge-line at the beginning of the horizontal curve, or on the inside edge- line at the end of the horizontal curve. This is a visual defect. It is illustrated in Figs Cl(a) and Cl(b). C.6 Corrective action consists of increasing the 28 separation between the curves The vertical curve overlaps one end of the horizontal curve C.7 If a vertical crest curve overlaps either the beginning or the end of a horizontal curve, a driver's perception of the change of direction at the start of the horizontal curve may be delayed because his sight distance is reduced by the vertical curve. This defect is hazardous. The position of the crest is important because vehicles tend to increase speed on the down gradient following the highest point of the crest curve, and the danger due to an unexpected change of direction is consequently greater. If a vertical sag curve overlaps a horizontal curve, an apparent kink may be produced. This visual defect is illustrated in Fig C1(c). C8 The defect may be corrected in both cases by completely separating the curves. If this is uneconomic, the curves must be adjusted so that they are coincident at both ends, if the horizontal curve is of short radius, or they need be coincident at only one end, if the horizontal curve is of longer radius. Both ends of the vertical curve lie on the horizontal curve C.9 If both ends of a crest curve lie on a sharp horizontal curve, the radius of the horizontal curve may appear to the driver to decrease abruptly over the length of the crest curve. If the vertical curve is a sag curve, the radius of the horizontal curve may appear to increase. An example of such a visual defect is illustrated in Fig C1(d). The corrective action is to make both ends of the curves coincident, or to separate them. The vertical curve overlaps both ends of the horizontal curve C.10 If a vertical crest curve overlaps both ends of a sharp horizontal curve, a hazard may be created because a vehicle has to undergo a sudden change of direction during passage of the vertical curve while sight distance is reduced. C.11 The corrective action is to make both ends of the curves coincident. If the horizontal curve is less sharp, then a hazard may still be created if the crest occurs off the horizontal curve because the change of direction at the beginning of the horizontal curve will then occur on a downgrade (for traffic in one direction) where vehicles may be increasing speed. C.12 The corrective action is to make the curves coincident at one end so as to bring the crest on to the horizontal curve.
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C.13 No action is necessary if a vertical curve that has no crest is combined with a gentle horizontal curve.
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