Stopping sight distance on grades

[jharris]

If I'm given a question where two connecting grades are given and the answer either asks specifically for SSD or asks for a related element (i.e. length based on SSD) for a given design speed, how could I get the SSD information using AASHTO? In the 2001 AASHTO book, for example, Exhibit 3-2 "Stopping Sight Distance On Grades" gives distances for either downgrades or upgrades. But, if I have a problem with both down and upgrades specified, how would I determine the SSD?

 

[Ambrug20]

If you given grades, you can find K=L / A. Use Green Book p. 270-277. you can find K-value, base on the tables from Gr. Bk or graphs in CERM p.78-14.

Knowing V and K you can find L or SSD

 

[ptatohed]

Ambrug, AASHTO GDHS pg 270+ covers vertical curves. I don't think that's what jh is asking about, right?

jh, I am not sure what you mean by both downhill and uphill. Can you give an example problem? Either the vehicle is traveling on a grade (-G% for downhill, +G% for uphill) or on level ground. Use Exh 3-1 or formula 3-2 GDHS pg 112/113 for SSD on level ground; or Exh 3-2 or formula 3-3 GDHS pg 114/115 for SSD on grades. Note that Exh 3-2 includes driver reaction time (1.47 V t) but eqn 3-3 does not. Add '1.47 V t' to eqn 3-3 to get the values in Exh 3-3.