On Sat, Nov 28, 2009 at 4:51 AM, Liz <ed...@billiau.net> wrote:
> On Sat, 28 Nov 2009, Paul Johnson wrote:
>> I should probably point out that not all roundabouts are one-way.
> That's a traffic circle
>
> I have researched this point......
>
>
> Liz
Here is the definition of "traffic circle" in wikipedia:
"A traffic circle is one of several types of circular intersections.
Traffic is normally allowed to go in one direction only around a
central island. In the absence of signs or signal control, traffic
entering a circle has the right-of-way, although many circles give
right-of-way to the primary roads or to circulating traffic. In
roundabouts[1] and rotaries[2] entering traffic must yield to traffic
already in the circulatory roadway, though this is not always true of
traffic circles.
While more precise definitions exist for roundabouts and rotaries, the
term "traffic circle" is generally used by engineers to describe
circular intersections that lack the defining characteristics of
roundabouts or rotaries. Therefore, traffic circles generally have one
or more of the following features that roundabouts and rotaries would
not:[citation needed]
* Right-angle intersections between approach roadways and the
circulatory roadway, or tangential approaches that allow full-speed
entry (no flared entry).
* Circulating traffic yields to entering traffic at one or more
approach points.
* Exits allowed only from the outer lane of the circular roadway.
* Lane choice on approach is not necessary, lane changes may be
made within circle road.
* Pedestrians or other accessible land uses allowed within the
center of the circle.
"
Again, nothing about bidirectional road.
But anyway, this is interesting as even if someone finds a single
example somewhere in the world of a bidirectional roundabout, it is
not a reason the remove the implied oneway=yes for the tag. It was the
same discussion about the implied bicycle=no on motorways everywhere
excepted in some cases in US. The problem with implied values is when
it is not true for a whole country and not only in a small number of
exceptions. Then the default is country specific and should be
documented separetely in the wiki for each country. Then it will be
the job of the routing applications to know on which country they are
before they apply some default values (but this is an easy job for
such application to know where they are, isn't ?)
Pieren
http://wiki.openstreetmap.org/wiki/Country_specific_default_values
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