Stopping Sight Distance

[rjh03]

Hi,
It is noticed in the newest version of AASHTO (highways) that the vertical curve length calculated from the SSD (stopping sight distance) is modified relative to that of the previous version; however, this modification is to the worse not to the better.
So, in the newest version (pages 271,272), Length L is calculated as AS2/658(when S is less than L) compared to AS2/404 in the 1994 version. The difference between the 2 results is mainly due to the change in the object height from 15 cm in 1994 to 60 cm in the new version. Hence by decreasing L the design speed on the highway is reduced and consequently reduction in quality of the highway.
So what do you think about that. Any interpretations are welcome.

Regards...

 

[wolfhnd]

This has been noted by several people I know and they entend to to keep using the old standard. Sight distance is a pretty basic highway design standard and the fact that so little has been writen about this change bothers me too. I think it should be 20" min for the object because that is about the height of the stop lights on a small car.