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.
The idea behind adding special markings for computers is that you can waste a lot of time and effort trying to perfect algorithms interpreting signage optimized for human consumption, or... you can spend much less time and effort, to much better effect, setting up additional signage that's easy for computers to consume and provides information relevant to computers (which is not necessarily the same as what humans need).
Note that roads are controlled, artificial environments. There's always someone responsible for maintaining a road and signage on it. The infrastructure to deploy additional markings dedicated to self-driving cars already exist.