
282 Forensic Engineering Fundamentals
e component of the weight in the same direction as friction is
e centripetal acceleration component of the superelevated road is
aA
V
r
==co
co
2
Summing forces
fW WM
V
R
W
g
V
R
cossin co
osΦΦ
+= =
(9.170)
f
V
gR
sin
cos
Φ
Φ
2
tan
sin
Φ
Φ
===S Superelevation
Sf
V
gR
+=
2
S
V
gR
f= −
2
(9.171)
Standard road design handbooks specify f as the side friction factor with a value of 0.16 for
speeds of 60 mph or less or 0.14 for 70 mph speeds. Additionally, the speed V earlier is to be
75% of the design speed. Equation 4.76 becomes negative for values of
f
V
gR
>
2
(9.172)
Since negative values of S mean that the superelevation ...