A new transportation engineer is charged with the design of a horizontal
curve for the Queen's Highway in Canada. His final design calls for a curve with a
radius of 520 meters. Would you sign your name to his plans?
Assume that the design speed for the Queen's highway is 110 km/h. You can also
assume that snow and ice will be present on the roadway from time to time (it's Canada).
[Solution Shown Below]
Solution
The first step in a review of his plans would be to make sure that the curve radius as
designed is greater than the minimum curve radius. For a design speed of 110 km/h,
the comfortable side-friction factor is 0.10. In addition, since the roadway will be
covered with snow and ice from time to time, the maximum superelevation rate is 8%. With
this information we can go ahead and calculate the minimum curve radius using the equation
below.
Rmin = V2/(127(emax/100+fmax))
Where:
Rmin = Minimum radius (m)
V = Design speed,110 km/hr
emax = Maximum superelevation rate, 8%
fmax = Maximum side-friction factor, 0.10
Substituting and solving yields a minimum radius of 530 meters. The 520 meter
radius that is called for in the plans would probably work, but it might be uncomfortable
for the vehicle occupants. A larger radius would be more appropriate.