From:
ANTONI FACEY
To: geno@ksu.edu
Subject: Roundabouts
Date sent: Mon, 16 Sep 2002
Dear Gene
I understand from Ian Appleton that you are looking for pictures of
roundabouts. I have designed a few that I am fairly happy with
(obviously I
would change things with the benefit of hindsight but they still work
well).
I have checked the crash records and all have met the criteria of
reducing the crash rate from the previous control and the crashes are
of
lower severity than previously. One intersection had 3 cycle crashes
but
none after the roundabout was installed; not the usually expected
result.
On this measure, you can say they are good roundabouts but there is
still
some room for improvement. I could probably get copies of the aerial
photographs from the local authority if you like. All of them are non
standard with difficult horizontal approach geometry.
There are a few things that I have found in my city that I have not
sen
anywhere else. I have spoken to others and they have never heard of it
either. We have the ring around our roundabout circulating islands to
allow
for tracking of heavy vehicles. These were constructed using the same
interlocking concrete block paving as the footpaths (not my choice).
Pedestrians now regularly walk around the inner circulating ring where
they
should not be. You should be careful that designers do not carried
away
with landscaping features such as that to the detriment of logical
arguements.
As a safety auditor, I have seen many roundabouts around NZ and I am
quite satisfied that the roundabouts I see these days are much better
than
those in the past. Almost invariably, they have good geometry or only
minor
faults, but the finishing touches such as landscaping and roadmarking
often let the result down. I post construction audited one last week
that
had been planned and designed as a 2 lane roundabout then a decision
was
taken to drop the roundabout to a single circulating lane without
physically
altering the approaches. Neither of us in the team could accept that
it
should work safely but when observing behaviour, there appeared to be
no
problems. The drivers sorted themselves out well. It was a larger
roundabout with only 3 approaches so that may have had something to do
with
it.
You should be aware that in Christchurch City which was the first city
in NZ to really begin the widespread use of roundabouts about 30 years
ago,
many of the roundabouts are being replaced with traffic signals. There
are
not many new ones being built there. This is due to the capacity
issues
of increasing traffic volumes.
One reason we have had so many roundabouts in NZ is our funding
regime.
It is much easier to financially justify a roundabout than traffic
signals
since you do not have the same impact on main road traffic flow as
with
traffic signals and off peak they are more efficient. Hence, we have
had
some roundabouts put in where they should not have gone for technical
reasons. When the roundabout is the do minimum, it becomes easier to
justify traffic signals.
A common fallacy is that you should not have any plants, etc on the
circulating island. I have found through my crash investigation
studies and
safety audits that this is not the case. I have even audited a site
where
we erected a large concrete architectural structure in the circulating
island. The approaches took care of all of the deflection through the
horizontal alignment and it was not possible for a vehicle at the low
design
speeds to strike the structure. There was enough visibility left for
vehicles at limit lines to determine the intentions of the circulating
vehicles safely.
I am happy to discuss these issues further if you would like but I do
not have many photos. To get photos, I would need to be in that part
of the
country and that depends on where my next client takes me.
Regards
Antoni Facey
BE (Civil), Registered Engineer
39 Quarry Road
Timaru
Telephone (03) 684 6665
Mobile (021) 148 7851
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