All of the things you mention will vary based on use of the data and choices made in the database schema. So the short answer is, it depends.
Most maps wouldn't uniquely identify a particular road segment. Some might do it by cross streets (x between y and z) and other might do it by address ranges (the x hundred block of y). However the data behind the map probably would utilize something like an address range, assuming as in the case of Google Maps it can be used to provide directions to a specific location. And within the data itself, every feature (whether that's an entire road line or a segment from one intersection to the next) has a unique id of some sort.
Everything else (and even address ranges) must be decided on a case by case basis. If one direction is different than the other, you'd need separate attributes at the least and possibly separate features. If one direction has three lanes and the other has six, that could be done with attributes. If AB is physically different than BA, it probably would be two features. In the case of divided highways, sometimes each travel direction is stored as a separate feature and sometimes it's a single line with a cartographic representation that just shows it as two separate features.
Attributes are usually classified as tofrom or fromto if they differ for a single line segment. For instance addresses may only be even on one side and odd on the other. This tofrom property is related to how the actual line geometry is drawn (start and end points), and also ties into travel direction/restrictions.
There are a host of possible attributes to consider for any given section of road. Whether those could be modeled using just attributes or separate features depends on any use/analysis that will be performed on the data and the requirements of symbolizing such data on a map. Streets maintenance, emergency response, navigation, route planning, or whatever other use you can think of might all have entirely different approaches to storing the same basic data based on their different attribute and use requirements.