Blog Archives
Stopping Sight Distance
The stopping sight distance (SSD) is the total distance you travel during the time you (a) react to apply brakes, (b) apply brakes and actually begin to decelerate, and (c) vehicle comes to a stop.
Reaction time from AASHTO (\( t_R\)) is 2.5 s.
Default deceleration rate from AASHTO is 11.2 \(ft/s^2\)
The total distance traveled using these values on a straight path is:
$$ SSD = Vt_R + \frac{V^2}{2(a\mp gG)}$$
Vertical Curves
Vertical Curves are nice! I think they are easier to solve than Horizontal Curves because they are essentially parabola equations (which you should be very used to). This is the formula for vertical curves
$$ y(x) = y_{PVC} + G_1x + \frac{1}{2}Rx^2 $$
\(y(x)\) is the elevation y at x horizontal distance into the curve from the start position
\(y_{PVC}\) is the starting elevation at x = 0.
