SSD for horizontal curve vs straight road

[ketanco]

In the formula

HSO = R x (1 - cos (28.65 x S) / R )

1) is this SSD the same SSD that we would find when we are considering a straight not curved road? because this is for braking right? both the reaction and the braking portion?

2) and in general unless otherwise is told to us, SSD means stopping sight distance for the things belonging to braking only correct (raction time + braking time) ?

3) and when we consider the vertical curves, this SSD is still applicable?

 

[ptatohed]

1. Yes, S (stopping distance) in the HSO formula you posted is calculated the same way as SSD (Stopping Sight Distance) which is 1.47 V t + 1.075 (V2/a)

Includes reaction and braking distance.

2. I think that is safe to say. There is also a DSD (Decision Sight Distance) to calculate the required distance needed to make a certain avoidance maneuver (which is the exact same formula as the SSD formula but with varying values for t, depending on the maneuver) but I think this is PM level stuff, you shouldn't see this on the AM. There is also passing sight distance but I think that is PM level too.

3. Not sure I understand the question?

 

[John QPE]

3) In a vertical curve the SSD will be a function of the curve, your measurement is different, and the line of sight will be drawn on a profile.

On a straight run of road, you may have 500 ft line of sight, but with a vertical curve, you may only have say 250 because of the curve.

I know I did not explain that too well.

 

[ketanco]

thanks a lot