(civl261)[2009](s)Quiz6Asolutions~PPSpider^_10068[1]

(civl261)[2009](s)Quiz6Asolutions~PPSpider^_10068[1] - =...

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CIVL 261 – Traffic and Transportation Engineering Tutorial Quiz 6A March 20, 2009 Name : Student ID : Geometric Design of Highways – Crest Vertical Curve For a design speed of 70 mph, f = 0.29, calculate the minimum length of a crest vertical curve with G 1 =+3 % and G 2 = -1 % that meets the 1984 AASHTO criteria for minimum SSD and desirable SSD. Solution: Design speed = 70 mph. From Table 3.1, the speed condition is distributed between 58 mph and 70 mph. Minimum SSD For minimum SSD, we use average running speed at 58 mph. So () ( ) () ft vt G f g v SSD r 647 5 . 2 47 . 1 58 03 . 0 29 . 0 2 . 32 2 47 . 1 58 2 2 2 = × × + × × × = + ± = Assuming SSD > L, then (rejected) 647 962 4 1329 647 2 1329 2 ft ft A SSD L m > = ×
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Unformatted text preview: = − × = Assuming SSD < L, then (accepted) 647 1261 1329 647 4 1329 2 2 ft ft SSD A L m > = × = × = So, the minimum length of the crest curve is 1261ft. Desirable SSD For desirable SSD, we use design speed at 70 mph. So ( ) ( ) ( ) ft vt G f g v SSD r 890 5 . 2 47 . 1 70 03 . 29 . 2 . 32 2 47 . 1 70 2 2 2 = × × + − × × × = + ± = Assuming SSD > L, then (rejected) 890 1447 4 1329 890 2 1329 2 ft ft A SSD L m > = − × = − × = Assuming SSD < L, then (accepted) 890 2382 1329 890 4 1329 2 2 ft ft SSD A L m > = × = × = So, the minimum length of the crest curve is 2382ft....
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