Problem 3 10 pts Drivers must slow down from 70 mph to 60 mp

Problem 3 (10 pts). Drivers must slow down from 70 mph to 60 mph to negotiate a severe curve on a rural highway. A warning sign for the curve is clearly visible for a distance of 100 ft. 1) H low far in advance of the curve must the sign be located in order to ensure that vehicles have sufficient distance to safely decelerate? (Use the standard acceleration and ed by AASHTO.)

Solution

Total Stopping distance is the sum of the reaction distance and the braking distance, such that ;

d=d_{r +} d_b =1.47S_t +[ ( S_i ²- S_f² ) / 30(F/0.01G) ]

In this case, the reaction time, t, is the AASHTO standard, or 2. 5 s. The friction factor, F, is based upon the standard AASHTO deceleration rate of 11.2 ft/s² (F = 11.2/32.2 = 0.348) and the speed is given as 60 mph.

d = 1.47*70*2.5+ [ (70²-60²) / 30* 0.348 ]

d = 257.25 + [ (4900-3600) / 10.44 ]

d = 257.25 + 124.52

d = 381.77 ft.

Since the sign can be seen clearly @ 100 ft.

Then the position of the sign should be :

= 381.77 - 100 = 281.77 ft