At 2010-07-04 13:41, Alan Millar wrote:
How are people using the "lanes" tag on motorways? Do you count the
on/off ramps that come and go?
Generally, no.
On a lot of the freeways near me, they have two main driving lanes on
each direction, so I set it up as a dual carriage way with one-way on
each side, and mark each side as lanes=2.
The question comes in for the on/off ramps. There are sections where
two intersections are somewhat close together, and so there is an on-
ramp, a long extended merging lane, then the next off ramp.
Strictly speaking, there is a third lane for some distance between
the the ramps, but it isn't a "through" lane. There are only 2
driving or through lanes in that section of freeway.
See for example hwy 217 between Denney and Allen at:
http://www.openstreetmap.org/?
lat=45.473345&lon=-122.786743&zoom=18&layers=B000FTT
I generally, form the intersection of the ramp with the main roadway at the
point where the solid line starts or ends - the first place you can legally
merge from an onramp or the last place to an offramp. In this case, this
leaves too short a section of 3-lane main roadway to bother breaking it
just in order to tag that short section with the extra lane. I see the
lanes tag being useful primarily in determining likely speed possible in
making routing decisions, other factors being equal. It could also be
useful in rendering. Neither would seem to sway me to add the extra lane
for such a short distance.
I-10 in this area
http://www.openstreetmap.org/?lat=34.03753&lon=-118.280316&zoom=18&layers=B000FTF
might end up being an exception in some places (I didn't look closely, but
it comes to mind).
I have only been counting the driving or through lanes, so I have
tagged this as lanes=2, and just ignored the short extent of the
extra merging lane.
Agreed.
Likewise, there are suburban streets that have an extra turn lane
just before an intersection, like Murray Blvd at:
http://www.openstreetmap.org/?
lat=45.4814&lon=-122.8261&zoom=18&layers=B000FTTT
As one big street with two driving lanes each direction, I've tagged
it as lanes=4 and ignored the short extent of the extra turn lane.
Because that center lane is present between intersections as a center turn
lane, I tag lanes=5. This, to distinguish it from roads where there are
only 4 lanes (2 in each direction) for the stretches between intersections,
since left turns without that center turn lane cause more congestion (again
thinking of speed estimation).
And one more variation is the suburban boulevard with one center
lane, only allowed to be used for turning/merging in and out of
driveways. I consider this like the freeway merging lanes; I've just
been counting the driving lanes and not the turning lane also. See
Canyon Road at:
http://www.openstreetmap.org/?
lat=45.489479&lon=-122.799664&zoom=18&layers=B000FTTT
This looked the same to me as the one above. I tag lanes=5.
--
Alan Mintz <[email protected]>
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