Hi,
Out of curiosity, what "local mapping guidelines" are you referring to here that led you to tag this route as trunk? Are they documented anywhere?

For context, consensus has emerged across the US to tag trunk routes by their importance to the road network rather than by physical characteristics, see https://wiki.openstreetmap.org/wiki/United_States/2021_Highway_Classification_Guidance. As part of this, I and other mappers developed California state guidelines to adhere to this concept. You can read them here: https://wiki.openstreetmap.org/wiki/California/2022_Highway_Classification_Guidelines. In particular, we documented this particular route as being best-tagged as highway=primary + expressway=yes, to reflect the fact that it does not connect major population centers, but is still built to near-freeway standards that allow for high speeds.

Happy to discuss these guidelines and the thought process behind them, and whether any modifications to various documented practices are necessary.

Best,
Will