Taken from "The Custom Bicycle" in 1978 by Kolin and De la Rosa

Since a road bike is fitted with brakes, the fork blade must be oval to eliminate the shuddering which would otherwise result under hard braking. Track Bicycles, which have no brakes, have round fork blades due to the greatly increased stresses caused by centrifugal force and side-loading caused by the banking of a track. Since tracks have a smooth surface, the neccesity for a fork to act as a shock absorber is reduced.