As indicated in Fig. 6.12, the main factors considered in determining the need for barriers are the embankment height and the side slope. These criteria are based on studies of the severity of encroachments on embankments as compared with impacts with roadside barriers. The figure does not include the probability of an encroachment or relative costs. Some states have made their own studies and developed charts having a series of curves for different traffic densities.
FILL SECTION HEIGHT (m)
FIGURE 6.12 Embankment warrants based on comparative risk analysis. (a) SI units; (b) U. S. Customary units. (From Roadside Design Guide, AASHTO, Washington, D. C., 2002 and 2006, with permission)