> See "Big Three of Shatin" (Tai Wai, Sha Tin and Fo Tan) all only has `highway=tertiary` to connect to them.

Which roads specifically are you talking about?

> CPR (Ko Po - Ngau Tam Mei) tends to use Yuen Long Station instead. (See KMB 76K, and the many minibus routes.)

I think public transport go to Yuen Long only because it's a major town whereas KSR station is basically in the middle of nowhere. As for private cars, Yuen Long does not have park and ride facilities, does it? And even if it does, it would probably still be less attractive due to the congestion in Yuen Long and the higher parking fees from a busier location.

And even if CPR does indeed prefer Yuen Long, Kam Tin and Pat Heung still have enough population to justify a `=secondary`. Pat Heung Road doesn't serve CPR nor Kam TIn (due to the Kam Tin ramp on Route 3), but it's still `=secondary`.

> Northern Link (construction is starting) is reducing importance of KSR station in terms of actual passenger in-out count via KSR station; would go in/out at Northern Link stations instead.

I don't understand this sentence at all. How does Northern Link (transfer passengers) affect in-out count? The only station whose in-out count might be affected would probably be Yuen Long due to the B1, 64K, etc. Or are you saying that fewer people would drive from CPR to KSR because they could have taken the train instead? But didn't you just say that CPR is going to Yuen Long?

> afaik in rural context, `highway=secondary` must have some sort of cross-district capability (e.g. Kam Tin Road, etc.). I don't see Kam Ho Road has this.

Given the PTI and park & ride at KSR, it's pretty clear that cross-modal transfer is encouraged and/or popular. Then, the West Rail can simply be seen as an alternative to Route 3, being cross-district. When Tung Wui Road and Kam Ho Road are the only ways to access KSR Station, they can be seen as an extension of the West Rail, which is cross-district, making Tung Wui Road and Kam Ho Roads themselves cross-district. This is practically quite similar to the "no change in highway classification without junction" rule: when you consider the rather remote location of KSR station, most people (except perhaps the residents of the new developments) using it are probably continuing their journey (using Tung Wui or Kam Ho roads) anyway, so the cross-districtness of the West Rail can be inherited to the roads.