Humans rely on road lines and signs as well and when those are covered, human capability is reduced and they have to drive slower.
For snow that generally disrupts the sign fiducial, we had a few solutions. The first is that if fiducials are dense enough, then dead reckoning may be sufficient until the next fiducial is observerd. The second is to try and build different layers of data with different error correction capabilities. One system developed could relay a low number of bits from a far distance and reasonable error correction capability. The remaining bits were then much smaller and readable from up close. The thought being that if you are able to fully resolve a fiducial in one area then assuming an apiori map of fiducials, the first 16 to 24 bits of a 64 bit code is likely enough to accurately resolve location.