On 01:11 2013-11-27, Peter Davies wrote:
Martijn,
I think it would be conceptually clearest for all the 2-way single
carriageway ways to point the same way and would suggest that this
should normally in be the direction of increasing milepoints/pointes
kilometriques (usually northwards or eastwards). At Castle Rock we
call this the positive travel direction (increasing linear reference
values) while the decreasing milepoint direction (reducing
milepoints/pointes kilometriques) we would call the negative direction.
It would be great for us if OSM forward tied in with milepoint increases.
Inevitably there is an occasional glitch in states such as Idaho where
"DOT milepoints" actually reverse direction for sections of 2 or 3 state
routes statewide, due to legacy signposting and route redesignation, but
this is probably less than 1% of routes nationally. More common is minor
milepoint jumps (where routes have been shortened by new construction)
and minor milepoint repeats (where bypasses are longer than the original
through route; a situation that Washington State calls backmiles and
Caltrans calls formulas). Despite this, there is almost always a mostly
consistent increasing milepoint (OSM potential PK tag) postive travel
direction that could become OSM forward on 2-way single carriageways.
In Ohio, non-freeway reference markers reset to 0 at each county line
along a route. As far as I can tell, though, the markers never count up
in one county, then down in the next. So I suppose one carriageway could
have increasing markers as it goes east across County A and continue to
have increasing markers as it continues south through County B, as long
as the route goes east-west overall.
It appears that freeway mile markers do not reset at county lines, but
cardinal directions may. On loop freeways, the mile markers increase
clockwise through all four cardinal directions. So traveling clockwise
on I-275 (which goes around Cincinnati), the mile markers increase
continuously, but the signposted direction is East in Hamilton County,
South in Clermont County, and West upon reentering Hamilton County and
in Northern Kentucky. I'd imagine the same thing applies to loop
freeways in most states. (Or is there such a thing as
"counter-clockwisebound"?)
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