Using the principle of conservation of energy we can equate the change in

# Using the principle of conservation of energy we can

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Using the principle of conservation of energy, we can equate the change in kinetic energy to the work done in moving the vehicle by the braking distance: Therefore Where, v = initial velocity of vehicle when brakes are applied (meters/sec), V = initial velocity (km/hr), g = acceleration of gravity (9.8m/sec.sq) f = coefficient of friction between tires and road surface (for dry pavements 0.6-0.55 at 50kph – 110kph. Much less values for wet pavements) Effect of Grade on Stopping Distance : Where, g = gradient (%; positive if uphill and negative if downhill) Values of recommended (minimum) stopping sight distances by design speeds and grades, as well as values of coefficient of friction (f) are provided in the relevant standards . Thus the minimum stopping sight distance (MSSD) = 2 1 2 MV Mgf d 2 2 2 254 v V d gf f 2 2 254( /100) V d f g 2 1 2 10 36 254( /100) V d d Vt f g
IDL Lecture 2 on 8-9/03/14 14 DESIGN CONTROLS AND CRITERIA MEETING SIGHT DISTANCE: This is the distance required to enable the drivers of two vehicles traveling in opposite directions to bring their vehicles to a safe stop just before they meet after becoming visible to each other. It is normally computed as twice the minimum stopping sight distance. It is desirable that the meeting sight distance is achieved along the entire length of the road for a single carriageway, especially where the carriageway width is less than 5.0m, as safe passing on such narrow roads can only be done at reduced speed. PASSING OR OVERTAKING SIGHT DISTANCE (OSD): This is a key design criterion for single carriageway roads (two lanes carrying traffic in opposite directions). In order to overtake slow moving vehicles a faster vehicle needs to use the lane of opposing traffic. If this is to be accomplished safely, the vehicle driver must be able to see enough of the highway ahead in the opposite traffic lane to have sufficient time to pass and then return to the right traffic lane without cutting off the passed vehicle and without interfering with the speed of the oncoming vehicle. The frequency of overtaking opportunities affects not only safety of operation but also the capacity of the highway, as faster motorists are constrained by the speed of slower ones from filling gaps in the traffic stream. Factors that affect MOSD are the judgment of overtaking drivers, the speed and size of the overtaken vehicles, the acceleration capabilities of overtaking vehicles, and the speed of the oncoming vehicle. Driver judgment and behavior vary considerably and the MOSD selected should be adequate for the majority of drivers. Empirical research has established minimum overtaking sight distances for design purposes.
IDL Lecture 2 on 8-9/03/14 15 DESIGN CONTROLS AND CRITERIA D1 represents the distance traveled by a vehicle while its driver decides whether or not to it is safe to overtake the vehicle in front. The time involved is the ‘hesitation time’ and is about 3.5seconds for comfortable driving conditions.

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