From Wazeopedia

Occasionally, if deemed necessary for proper routing, a particular road's type may be set higher than as prescribed in these rules. If a road has a higher type than set forth in these rules, there may be a reason for it.

Long Route Continuity As Waze calculates longer routes, it prunes lower road types from its route selection in favor of higher road types. If a road segment connects two much higher road types (e.g., a primary street connects a major highway to a freeway), Waze will choose not to route over that lower segment even if it is much faster. In order to ensure the best possible routes are chosen, these segments will have to be set higher to encourage routing over them.

Promotion of a connecting road is warranted if the road is signed as the designated route from one road to the other. For example, a freeway exit may be signed as "to a particular highway", but the only way to get to that highway from the exit ramps is over a lesser road. Where such connections are supported by signage, the road type of the connecting road should match the lower of the two roads that it connects, up to major highway (In the USA a road may only ever be set to freeway if it meets the criteria of the Freeway section). Promotion of connecting roads preserves routing continuity and prevents Waze from pruning out valid routes.

A segment's road type can be upgraded in unsigned circumstances.