[Talk-us] Prima Facie Speed Limits

Ed Hillsman hillsman at pobox.com
Mon Sep 15 14:59:11 UTC 2014

I agree there is a need to have a way to deal with this. Where I have checked a street, in both directions, for a posted speed limit and found none, I tag the street as maxspeed=unposted, source:maxspeed=survey. This makes it clear that the street has been checked in the field and found not to have a posted speed limit.

When I lived in Florida, it was in an area where two municipalities and the unincorporated county had jurisdiction over the streets. One city defaulted to 30 mph for unposted streets. The other, supposedly, defaulted to 25 mph, although despite repeated efforts I was never able to find the ordinance or regulation that set this. The unincorporated parts of the county defaulted to the state's default, which was 30 mph. The locations of the municipal boundaries were not accurate in OSM, so I felt uncomfortable tagging a street near a boundary with source:maxspeed=City_A_default etc.  So, I decided the best way to handle this was the scheme I described above. It records what's on the ground, and someone who wants to do something that needs a speed limit value can overlay an appropriate boundary or regulation or other default to fill in the values that are not clear on the ground.

I face a similar situation here in Albuquerque, where I map in the city (default of 25 mph), the county (defaults to the state's 30 mph), and Los Ranchos (whose default I haven't been able to ascertain definitively--although I haven't made a big effort). 

The maxspeed=unposted renders as an olive drab in http://www.itoworld.com/map/5, so this makes it easy for me to see at a glance which streets I've checked and which ones I haven't. And, if the larger OSM community agrees on a standard way to tag unposted streets, this tagging makes it easy and, I hope, unambiguous about which streets need to be retagged. The only streets that remain ambiguous then are those that have not been checked (which remain untagged for maxspeed), and those that have a different speed limit in each direction, with a long-ish stretch in between, leaving it unclear where the posted speed limit actually changes (for example, Coal and Lead in downtown Albuquerque, where transitions between two-way and one-way status compound the ambiguity). In these cases I do not tag the ambiguous section for maxspeed.

I guess I should mention that I'm interested in using speed limits (with other information) for bicycle routing.

Ed Hillsman
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