[Talk-us] What is a dual carriageway?

[Nathan Edgars II]

On 1/15/2012 12:31 PM, Hilton Long wrote:
> SR9 in Hurricane UT, has either 4 or 5 lanes. Two in each direction and
> the fifth a turning lane, that occurs for part of the road. Part of the
> road is limited access, but you can make a U turn on the part with 5
> lanes, and there is grade access from intersecting streets. The road is
> represented as two, two lane, one way streets for its entire length, but
> it has a FIXME tag that says “not a dual carriageway”.
>
> Should the 5 lane part, be shown as a single 5 lane road?

I most likely added the tag, so I'm biased :)

For some purposes (e.g. improvement of highways to four-lane divided by 
Georgia's GRIP program) a center turn lane (for the record, 
center_turn_lane=yes) counts as a median. But in general, if you can 
drive anywhere on the paved surface, it shouldn't count as a divided 
highway. For example, a pedestrian can take refuge in a median, but 
cannot do so (safely) in a center turn lane. A driver can turn left (and 
probably U-turn) anywhere. If there's an obstruction on the right side, 
you can cross the centerline to pass. At least in Florida, you have to 
stop for a school bus coming the other way if there's a center turn 
lane, but not if there's "an unpaved space of at least 5 feet, a raised 
median, or a physical barrier".

Essentially there are very few advantages to mapping it as two ways, and 
many to mapping it as one.