"Graham." wrote in message
...
On Thu, 05 Jan 2017 21:14:01 GMT, ScottRAB
m wrote:

replying to harry, ScottRAB wrote:
Modern roundabouts are the safest form of intersection in the world
(much
more so than comparable signals). Visit
http://www.iihs.org/iihs/topics/t/ro.../topicoverview for modern
roundabout FAQs and safety facts. Modern roundabouts, and the pedestrian
refuge islands approaching them, are two of nine proven safety measures
identified by the FHWA, http://tinyurl.com/7qvsaem
The FHWA has a video about modern roundabouts on YouTube, or check out
the
IIHS video (iihs dot org).

Roundabouts are great until the road planners make one of three silly design
decisions:

- Placing high barriers, hedges or signs on the central reservation as you
approach the roundabout, so you lose sight of traffic coming from your right
at the critical time when you need to see it, only regaining sight of it
again when you are virtually at the give way line.

- Placing new roundabouts off-axis of the major road so traffic on the road
with greatest flow has to deviate from the straight ahead route that it used
to take before the roundabout was there. https://goo.gl/maps/yVwWuTRgU4R2 is
an example: this shows the road before a new roundabout was put in.
https://s29.postimg.org/j24hmuymf/edencamp.jpg shows the new roundabout (in
red) and a new road to serve a large development near there. The green
circle shows where (IMHO) the roundabout ought to be. There seems to be a
tendency with modern roundabouts to direct traffic towards the centre of the
roundabout, with a tight left-curve in the last few feet, instead of
splaying the entry and exit lanes slightly to direct traffic tangentially
towards the outside of the central disc.

- Placing *raised* mini-roundabouts at junctions which used to be T
junctions, such that traffic turning right has to make a very exaggerated
left turn first of all to get onto the roundabout and to negotiate it
without the rear wheels bumping over the hump. If there is insufficient
space, the roundabout should be a painted disc so traffic can drive over the
middle, once the roundabout has done its primary job of establishing equal
priority to all the roads that lead into it.


But leaving those niggles aside, roundabouts are better than traffic lights
at busy times, though worse at quiet times when lights would give a
straight-through, no-need-to-slow-down-as-much route as long as you are
going straight on. With good sensors, lights can even give a quick route on
the road that has a red light, as long as the sensor temporarily turns the
lights green to let you through because there's no-one on the other road.

They are infinitely better than American four-way-stop junctions which make
everyone stop even if you can see that there is no traffic coming from any
other direction that you would need to give way to. I don't like junctions
which rely on order of arrival to determine priority, rather than according
to position on the road, ie priority to traffic on major road (at a
conventional major/minor crossroads) or to traffic coming from right
(roundabout). Priority determined by position is better than priority
determined by time of arrival. Any junction should have only one "winner"
(according to well-known rules) rather than ever giving the same priority to
two roads and relying on all the "I was here first / No *I* was here first /
OK, after you / No, after *you*" faffing about that you get with a
four-way-stop, which either leads to time-wasting stalemate or else crashes
:-)