Question

: A freeway exit ramp has a single lane and consist of entirely of a horizontal curve with a central angle of 90 degree and a length of 626 ft. If the distance cleared from the centre line for sight distance is 19.4ft, what design speed was used? Assumptions: t= 2.5sec, f=0.4

Answer 1

The design speed was used for the freeway exit ramp is 11 mph.

Design speed used in the exit ramp

The design speed used in the exit ramp is calculated as follows;

f = v²/15R - 0.01e

where;

• v is designated speed

v = ωr

v = (θ/t) r

θ = 90⁰ = 1.57 rad

v = (1.57 x 19.4)/2.5 s

v = 12.18 ft/s = 8.3 mph

Design speed

f = v²/15R - 0.01e

let the maximum superelevation, e = 1%

f = (8.3)²/(15 x 19.4) - 0.01

f = 0.22

0.22 is less than value of f which is 0.4

next iteration, try 10 mph

f = (10)²/(15 x 19.4) - 0.01

f = 0.33

0.33 is less than 0.4

next iteration, try 11 mph

f = (11)²/(15 x 19.4) - 0.01

f = 0.4

Thus, the design speed was used for the freeway exit ramp is 11 mph.

Learn more about design speed here: brainly.com/question/22279858

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