Stopping Sight Distance CE 331 Transportation Engineering

Sight Distance Definition: The length of the roadway (or crossroad) ahead that is visible to the driver to enable a vehicle traveling at design speed to stop before reaching a stationary object in its path make a decision Pass Decide what to do at a RR Xing

Stopping Sight Distance (SSD) SSD = dr + db dr: distance traveled during the driver’s P-R time db: distance needed to stop the vehicle from the instant the brake is applied

SSD Formula SSD = 1.47Vtr + V2/[30(a/32.2+G)] Mixed unit equations: SSD = 1.47Vtr + V2/[30(a/32.2+G)] SSD: stopping sight distance (ft) V: vehicle speed (mph) tr: P-R time, use 2.5sec if not given a: deceleration rate (ft/s2); g=32.2 fps2 G: grade SSD = (0.28) tru + 0.u2/[(254)(f+G)] SSD: stopping sight distance (m) u: vehicle speed (kph) f: friction factor (note: f = a/g in appropriate units)

Example S = (0.28)t u + u2/[(254)(f+g)] 90 +0.03 1 0.15 Will truck strike tree? u=90 km/h; t = 1 sec; f= 0.15 3% 170 90 +0.03 S = (0.28)t u + u2/[(254)(f+g)] = 202.37 m 1 0.15 YES