[OSM-newbies] Highway Types and Speed Limits

[Alan Mintz]

At 2009-10-14 16:58, James Ewen wrote:
>...
>Default values does not mean that that is the only value that the way
>can have applied. What a default value does, is give a value that can
>be used in the absence of an explicitly defined value. If you do not
>have a default value, then you have to assume a null value. For speed,
>that would be zero. That makes for calculating an ETA pretty
>difficult.
...
>One thing that can be seen rapidly though, is that default values vary
>by jurisdiction. We need style sheets that can be applied to the map
>by area.


Exactly. I thought that, from my read of the Wiki way back when, the idea 
with road properties was to "tag by exception", and that, at some point, we 
would get around to defining what the default values should be in the 
absence of tags to the contrary. These would seem well-placed on admin 
boundaries, with smaller levels (e.g. cities) tagging by exception to their 
surrounding larger ones (e.g. states).

Example:

On California state boundary, I would tag the most common values:

(speeds shown in mph here for ease - converted to kph when actually tagged)

maxspeed=25
maxspeed:motorway=65
maxspeed:primary=45
maxspeed:secondary=40
maxspeed:tertiary=35

lanes=2
lanes:motorway=3 (assumes all motorways are drawn as two separate one-way 
roads - 3 lanes in each direction)
lanes:primary=5 (2 in each direction plus an alternating island/center turn 
lane)
lanes:secondary=5
lanes:tertiary=4

surface=paved
surface:track=unpaved

smoothness=good
smoothness:track=bad


So, a residential road with no lanes or maxspeed tag is assumed to be good 
smoothness, paved, 2 lanes (1 in each direction), and 25 mph.

On city boundaries for Rancho Cucamonga and Irvine, because some roads are 
wider and most are faster, I might tag (again in mph):

maxspeed:primary=50
maxspeed:secondary=45
maxspeed:tertiary=40
lanes:primary=7

To make the renderer's job easier, it is necessary to add the various 
is_in:* tags so it can easily find the defaults, right? Must roads then 
always be split at admin boundaries?


On a related subject, thinking of divided roads that have not yet been 
split (but should be), this would be nice:

lanes:primary=5 (for unsplit roads - 2 in each direction plus an 
alternating island/center turn lane)
lanes:primary:oneway=2 (for the split roads)


There is also the issue of separate truck speeds. In CA, freeways are 65 
mph, but 55 for trucks or vehicles that are towing. There are also inclines 
(like Cajon Pass) that have lower limits for trucks. I've been tagging:

maxspeed=113 (70 mph)
+ maxspeed:truck=64 (40 mph for trucks)

Does this seem OK?

--
Alan Mintz <Alan_Mintz+OSM at Earthlink.net>