To find the minimum curve length, the SSD formula is applied with the given velocity, perception-reaction time, and deceleration rate. Highway grades must be accounted for in the design, impacting SSD and curve length. Ignoring grades alters the SSD calculation and required curve length.
To determine the minimum length of the vertical curve for a highway with a design speed of 120 km/h, to meet the Stopping Sight Distance (SSD) requirements, you need to factor in the driver's perception-reaction time and the vehicle deceleration rate.
The SSD can be calculated using the formula SSD = vt + (v^2)/(2*a), where 'v' is the initial velocity (speed of the vehicle), 't' is the perception-reaction time, and 'a' is the deceleration rate.
Plugging in the values provided, we get SSD = (120 km/h * 1000 m/km / 3600 s/h * 2.5 s) + ((120 km/h * 1000 m/km / 3600 s/h)^2) / (2 * 3.4 m/s^2).
When calculating the actual length of the vertical curve, the grades before and after the curve need to be considered, as the grades will impact the visibility and stopping distance on the curve.
If these grades are ignored, it would have an effect on the calculated SSD and thus alter the required length of the curve.