1. A method of detecting road or lane identifiers, comprising the steps of: receiving an image of a road in front of a vehicle from a video imager; determining a region of interest in an identified road in the image using an image processing device; and detecting road markings by detecting lane markings in the region of interest, and if lane markings cannot be detected, then detecting road boundaries in the region of interest; wherein detecting road markings includes: determining luminance gradients in the region of interest; and detecting road markings by comparing the luminance gradients to a strength threshold; and wherein determining luminance gradients includes determining edge strength in the region of interest to identify potential road marking edges; and wherein detecting road markings includes comparing edge strength to said strength threshold by determining peaks and valleys in luminance gradients of image pixels, wherein a gradient peak represents an edge in the image, and a gradient valley represents an edge in the image; and wherein detecting road markings further includes for multiple image rows in the region of interest: identifying a pair of edges as potential road marking edges by comparing each edge strength to said edge strength threshold; determining spacing between the pair of edges; and comparing said spacing to spacing minimum and maximum thresholds; wherein if the edge pair spacing is between the minimum and maximum thresholds, then the edge pair represents a potential lane marking; passing a curve fit through the identified candidate points corresponding to edge pairs in said row representing potential lane markings; and selecting all edge pairs that contributed to an acceptable first approximate line fit, as lane marking identifiers.