So far, driving tasks and the associated CV approaches have been discussed on the basis of essentially planar scene models. Even traffic sign recognition could be handled by a picture domain approach, given `normal' highway or rural road conditions. Problems begin to aggravate, however, if traffic signs have to be looked for not only at posts planted near the road border, but also on arms or bridges extending across multiple-lane roads. Likewise, the 3-D structure of the environment has to be taken into account if the lane marking is provided by rows of beacons or posts or if the vehicle has to manouver through narrow underpasses or gates. The latter conditions rarely occur on highways, but rather tight situations may have to be coped with along road construction sites and in the vicinity of traffic accidents.
In innercity road traffic, 3-D analysis can not be avoided, not the least since vehicles and other objects may occlude part of the road limits or traffic lights. Not much has been published so far about such problems.