Interpreting Motorways for Rwanda
The OSM page of standard features shows the classification of roadways: https://wiki.openstreetmap.org/wiki/Map_Features#Highway. The photos and descriptions show a bias toward European and Western road systems which requires some interpretation for less developed transportation infrastructures such as Rwanda. The following is intended to reflect the unique features of Rwandan roadways with appropriate classification standards.
The NR (National Road) road system in Rwanda should be classified as a Trunk Road. This is regardless of the quality of the road surface since a trunk road is a primary roadway. Most of the NR roads are classified as Trunk Roads, but there are some which may be one classification lower Primary Road. An example is NR20 from Base to Byumba.
After the NR roads, Rwanda has the DR class of road. These should be classified as Secondary roads. All remaining roads, if they connect more than one village should be classified as Tertiary roads.
Interpreting the Classification of Country Roads
Once in the countryside, it becomes somewhat more problematic to consistently classify the roads. Most are simple dirt roads which, it could be argued, should be classified as: Unclassified Road, Residential Road, or Tertiary Road. For the sake of consistency, I would like to propose the following suggestion.
According to Open Street Map's highway classification wiki page (see https://wiki.openstreetmap.org/wiki/Map_Features#Highway), the classification of the roads has nothing to do with the quality of the road surface. Technically, a track through a field can be classified a primary road if it is a link between two major cities. The key factor is not the road quality or size but the importance of communities being connected.
While it would seem logical that a Primary Road on the OSM map would imply that it is a larger road with a better surface, nevertheless, the rules say that road conditions are to be described in the tags, not in the classification of the road itself. So, let's work together to implement this scheme consistently.
Suggested Rural Road Classifications
So, any road that connects more than two villages should be classified as a tertiary road. Try to avoid using unclassified road.
Roads that are inside towns or villages should be residential road (or track, or walking path. These designations are based on the size of the way). In some cases, a residential road may turn into a track and then turn into a walking path. The key consideration is whether a road connects to the next village; if so, it is a tertiary road or maybe a secondary road depending on the size of the communities it connects. If the road does not connect to another community, then it should be residential road as long as it has houses close together, unclassified road for a dirt road, track for a very basic road through fields etc. In many cases a track will turn into a foot path.
OSM encourages its contributors to make their own decisions when there is some doubt regarding a particular feature and so this contributor would suggest that, in the case of Rwandan roads.
Another unique challenge for road classification in Rwanda is the Residential Road. Arguably, every road in Rwanda is a residential road since there are houses lining almost every roadway. But it would be foolish to change the designation of an NR trunk road to residential as it passes through a town or city. It is better to use the area to select the town or village and use the designation Residential Area for all major roads that pass through towns and villages.