For a long time it was clear to me that a lot of the streets on OpenStreetMap were wrongly classified. But I didn’t have an answer on the fix. It was obvious that some mappers are using sources and that some may be using their own rational or “gut feel” to make updates or improvements. I too questioned some of the map results based on my “gut feel”, so I know what you are saying.
The issue here is that non of us mappers have the full understanding of all the parameters that go into classifying roads the correct way. And frankly, nor should we have to. It takes a lot of planning and transportation science to properly do these allocations. There is already an agency empowered to do just such a task. It is Caltrans. Since it is a state agency, there will not be any deviation from county to county. And also, since it deals with federal money, it has to align with federal standards, therefore ensuring that there is uniformity across states (OK – maybe with few exceptions). Any errors that will result from using Caltrans as the source will be a lot fewer that letting mappers without transportation knowledge do it based on individual understanding – even if a common rules approach is attempted. Currently I am finding that there are a lot of errors. And after carefully reviewing what is on OpenStreetMap with what is classified by Caltrans, Caltrans has it right – one thousand times better than what mappers are using. And when you look at the difference, you would realize that while you may disagree with some classification, you will definitely agree with it and that overall it is a much better approach. Keep in mind that the road signage that is physically out there is based on this map and all routing programs use the national map using these classifications.
The idea is to have uniformity across all mappers. There is no better way to achieve that – instead of having mappers make their own judgment. As you can see there is a difference in how the two of us see things – and this is just between two people.

Here is the map source: https://caltrans.maps.arcgis.com/apps/webappviewer/index.html?id=026e830c914c495797c969a3e5668538

Resource: https://dot.ca.gov/programs/research-innovation-system-information/office-of-highway-system-information-performance/functional-classification

One other thing -  I know you sent an email long ago about trunk road classifications. At the time I did not have a good answer to reply. 
Apparently, the idea is to keep Pacific Coast Highway between 22 and 55 as trunk. As well as the section North of Santa Monica through Malibu to be kept as trunk. I think this is a mistake. A trunk is for a true expressway and behaves similarly to a freeway. In my opinion, any road that has bike lanes and sidewalks for pedestrians can not be classified as trunk road. Moreover, the PCH in Malibu has garage doors opening right into the road – so you would have driveways connecting to the road. No way that is a trunk road. Also, with all the news about speeding and accidents in Malibu, are we contributing to the issue by wrongly giving some drivers the idea that it is a “fast” road by classifying it as a trunk when it is not? All of these can get us back to talking about Caltrans. They have these sections as a primary road – I agree with them 100%

Hope this helps

PS – Happy New Year!
