[Tagging] Stopping by request on one line but always stopping on another

[Minh Nguyen]

In San Jose, California, VTA light rail generally only stops when a 
passenger is waiting on the platform or has requested a stop on board. 
[1] This is already rare for heavy rail but especially unusual for light 
rail in the U.S., so I was glad to come across the request_stop=yes/no 
key. [2] It could allow a router to remind an end user of the need to 
request the stop. Unfortunately, there are a couple complications, so 
I'm hoping this list could point me in the right direction.

Each light rail station is also served by buses, so it's mapped as a 
railway=station bus=yes node that's part of a stop_area relation with a 
couple bus stops. [3] (I understand this to be correct according to the 
PTv2 schema, but please chime in if it isn't.) For now, I'm only 
interested in tagging request stops for light rail, not the whole bus 
system, so I was thinking of tagging the individual railway=stop nodes 
instead of the railway=station node. So far, so good.

It turns out that the light rail vehicles do stop without a request at 
some of the stations along the route. These stations are listed as 
timepoints on the posted schedule. I could tag these railway=stop nodes 
as request_stop=no, but some stops are served by multiple lines that 
have differing timepoints. For example, the Tasman station is a 
timepoint along the Green Line but only a request stop along the Blue 
Line. [4]

How should I indicate that the stop is only a request stop depending on 
the line? So far there's a suggestion to change the node's role in the 
route relation from stop to stop_request [5] -- or, based on the 
reasoning above, from stop_position to stop_request_position. But I'm 
wary of coining a relatively obscure relation role that could break data 
consumers and QA tools that strictly adhere to the PTv2 schema.

[1] 
https://www.vta.org/faq/how-do-i-start-riding-vta#accordion-5--signal-to-request-a-stop
[2] https://wiki.openstreetmap.org/wiki/Tag:request_stop%3Dyes
[3] https://www.openstreetmap.org/relation/9365492
[4] https://www.openstreetmap.org/relation/9365503
[5] 
https://wiki.openstreetmap.org/wiki/Talk:Tag:request_stop%3Dyes#Request_stops_per_bus_route

-- 
minh at nguyen.cincinnati.oh.us