Sight distance restriction on highways’ horizontal curves: insights and sensitivity analysis

European Transport Research Review

An Open Access Journal

Table 2 Maximum obstruction heights for a clear sightline in horizontal curves

Sight Distance (SD) Type	Maximum Obstruction Height for Horizontal Curve Sightline (*), in meters
Stopping SD (undivided highway)	(1.05 + 0.15)/2 = 0.60 m
Stopping SD (two-way (divided) highway	(1.05 + 0.60)/2 = 0.825 ~ 0.80 m (rounding down)
Decision SD	(1.05 + 0.60)/2 = 0.825 ~ 0.80 m (rounding down)
Passing SD	(1.05 + 1.05)/2 = 1.05 m

*Based on passenger car driver eye height of 1.05 m, object height of 0.60 m for multilane highways, object height of 0.15 m for two-lane highways, and portion of the vehicle height that needs to be visible for another driver to recognize a vehicle: 1.05 m
**The passenger car driver eye height and the object height for passing sight distance (1.05 m) were adopted from Israel Highway Design Guidelines [18]. These values are similar to the values proposed by AASHTO 2011 green book values (1.08 m)
***The SSD object height proposed value for two lane highways (0.15 m) is different from AASHTO (2011) assuming that in lower design speeds drivers are still able to see an object shorter than 0.6 m [18]