Vert Curve Stopping Distance

[ripcurl2151]

I know this is last minute, but I'm still a little confused about finding vertical curve lengths based on stopping sight distance. I know how to use the different equations to calculate L for when S<L or S>L. But then there are also the tables for design speed and K values (ie Exhibit 3-72). You can also calculate L from this table using L=KA. It seems like a lot of the problems I have seen use the S<L, S>L equations first, but then go with L=KA as the answer. Are you supposed to do both and see which is larger?

Thanks for any help.

 

[sac_engineer]

I know this is last minute, but I'm still a little confused about finding vertical curve lengths based on stopping sight distance. I know how to use the different equations to calculate L for when S<L or S>L. But then there are also the tables for design speed and K values (ie Exhibit 3-72). You can also calculate L from this table using L=KA. It seems like a lot of the problems I have seen use the S<L, S>L equations first, but then go with L=KA as the answer. Are you supposed to do both and see which is larger?
Thanks for any help.

The largest stopping distance is usually the answer for safety purposes; however, the KA function is based on comfort criterion for sag curves and yields the minimum length of the curve for comfort, not the safest stopping distance based on speed and curve parameters.

The minimum length calculation is solely based on the point at which the driver is able to see over the crest and stop at the distance equivalent as if the road were flat. It is from this point back to the beginning of the curve where the minimum length is determined.