Highway Engineering class Exam Review el. A temporary diversion has been constru

Question

Highway Engineering class Exam Review el. A temporary diversion has been constructed on a highway of-35% gradient due to major repairs that are being undertaken on a bridge. The maximum speed allowed on the diversion is 15 mi/hr. Determine the minimum distance from the diversion that a road sign should be located informing drivers of the temporary change on the highway. Maximum allowable speed on highway 60 mi/hr. Letter height of road sign 5", Perception-reaction time 2 sec. Assume that a driver can read a road sign within his or her area of vision at a distance of 50 ft for each inch of letter height

Explanation / Answer

Solution - The coefficient of side friction factor for design speed of 60mi/hr, fs = 0.12

Now braking distance is calculated using the following formula,

db = ( Vi2 - Ve2) / (2g*( f + G))

Here Vi = Initial speed = 60 mph , Ve = ending speed = 15 mph , f = 0.12 , G =.035 , g = 32.2 ft/s2

Convert mph to fps by multiplying 1.4667 to mph value

so, db = 727.327 feet

Now distance dr for perception-reaction time is given by

dr = v*t = 60 mph *1.4667 * 2 sec=176.004 feet

so, ds = dr + db = 727.327 + 176.004 =903.331 feet

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