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SIDRA
Developed in Australia
Gap theory analysis
Geometric parameters partially considered
Used by about 90% of the country
Does signals, most other intersections also
Calculates emissions – CMAQ money…
Once SIDRA is
started the first real
step is to get your
lane configuration
correct.
What rule helps with
this?
Could use templates
to get to desired lane
configuration quicker
Here’s the quick version of how to run SIDRA
All of the lane
configurations in the
2009 MUTCD are
shown here
This could be used to
start analyzing the
447 interchange
NOTE: While the
templates are nice
and can speed up
the analysis time I
would rather start
with a single lane
roundabout and only
add lanes when
absolutely necessary
Here’s the quick version of how to run SIDRA – use template to get close
Go around the
roundabout to make
sure all the legs are
how they need to be
SIDRA will allow
some “odd” lane
geometry so make
sure it makes sense
Here’s the quick version of how to run SIDRA – finalize lane geometry
Use reasonable lane
widths, radii and
make sure the
correct number of
circulating lanes are
set
Set the Environment
Factor correctly –
who knows what
DOTD wants for
these values?
Here’s the quick version of how to run SIDRA – set roundabout geometry
Enter the turn counts
with the latest data
available.
Set the % Heavy
Vehicles and PHF
Here’s the quick version of how to run SIDRA – enter existing turn counts
Use Demand &
Sensitivity – Design
Life to check for
future years
May want to revise
Environment Factor
for future years –
why?
Here’s the quick version of how to run SIDRA – check future years
Anything seem
different than what
was just mentioned?
Do these steps agree with the DOTD SIDRA settings brochure?
Anything seem
different than what
was just mentioned?
Do these steps agree with the DOTD SIDRA settings brochure?
Does anyone know
how I feel about
HCM 2010?
It is based on a few
sites studied in the
early 2000s – how
many people here
drove roundabouts
daily in 2003?
In my opinion the
HCM 2010
roundabout capacity
model did more harm
than good – why?
What about US data? HCM 2010 to the rescue…?
FHWA requests an
update due to
complaints
Quite a few more
sites are now studied
– NY, IN, WA, VT…
Slide capture is from
teachamerica.com –
this site is a great
resource for
roundabout info
since all of the
presentations from
the TRB International
roundabout
conferences are
there
HCM 2010 was not well received by everybody
For single lane
roundabouts a
significant increase
in capacity was
discovered
Although the A value
increased the other
factors result in 2
laners not getting
that much more
efficient.
Once given some
thought, this makes
sense – most drivers
are now comfortable
with 1 laners but still
nervous @ 2 laners
Any differences between HCM 6 & HCM 2010?
PLEASE PAY
ATTENTION TO THE
NECESSARY
STEPS
1st - go to the
Roundabouts tab
2nd – click on HCM 6
That’s it…
What to do if DOTD wants to use HCM 6?
1st – lane geometry
doesn’t matter –
helps get agreement
between analysts.
This is a significant
bonus for those that
like results to agree –
as compared to
“close enough for
government work”
2nd – can still
calibrate to local
conditions by either
calculated numbers
or an overall HCM 6
model calibration
factor
Why would DOTD want to use HCM 6?
For 1 laners the EF
should to be set to
1.05 for current and
future year analysis
For 2 laners the EF
should be set to 1.2
for current year
analysis and to 1.1
for future year
analysis
Carmel, IN capacity
numbers are what
we hope most of the
US to get to in the
near future
How would DOTD adjust current SIDRA model to match HCM 6?
Washington State
has already made
the switch to HCM 6
in SIDRA
WSDOT already recommends the use of HCM 6
Washington State is
already noticing that
the HCM 6 formula is
a little conservative
for their state
DOTD could monitor
some of their own
sites or follow other
states that have
already noticed slight
differences
WSDOT already recommends tweaking HCM 6
Even near 0.6 V/C
the delay is low and
not too sensitive to
slight adjustments
either way – but – at
around 0.85 V/C a
slightly lower V/C
means a little less
delay but a slightly
higher V/C ratio
could mean extreme
delays – even failure!
Why do the delays seem to match better when delays are low?
A project in NY where a single lane roundabout
is expected to “fail” in the futureA second approach lane may be necessary when circulating vs. approach volume
sum > 1100 vphpland most likely necessary when sum > 1,400 vphpl
This example:
Approach volume = 1169
Circulating volume = 322
Circ vs. Approach = 1491 > 1100
Yes, a second approach lane is likely needed.
1491
Right Turn Lane NeededA right turn lane added to the layout now provided total sums of entering and circulating traffic
below the 1,100 vphpl warning level and definitely well below the 1,400 vphpl maximum
An additional lane only 200’ long allowed LOS to go from F to A/B in 20 years
This example:
Approach volume = 466 703
Circulating volume = 322 322
Circ vs. Approach = 788 < 1100 > 1025
Right lane works… Left lane works…
788
1025
It was decided that if
the roundabout
started to back up
towards the interstate
interchange then the
right turn only lane
would be re-evaluated
Upper management
was willing to risk
poor LOS for ½ hour
a day to keep the
single lane since it is
safer – as long as it
didn’t adversely
impact any nearby
significant
intersections
Here’s what was built – anything missing?
Here is the desired
roundabout design to
get good LOS
Upper management
wanted to know how
this would operate
without the WB move
being a double
through. Then they
wanted to know how
“bad” it would be if the
right turn only lanes
weren’t built yet
Existing intersection
was horrible due to a
lack of turn lanes
Another project where the design was altered with expected consequences
Right-in / right-out
access management
was utilized for the
Mobil gas station
A few right turn only
lanes are possible in
the future but only if
significant impacts
occur to nearby
highways. The
double through move
on 7 WB is no longer
possible in the future
A single lane roundabout with very good access management was built
Every couple of
weeks the leg from
the lower right will
back up to the light
green line.
It takes over 2
minutes to clear the
queue when it gets
this long
Once the I-890 exits
starts to get impacted
it will be interesting to
see what is done.
Most likely it will be a
metering signal to
allow this leg to work
more efficiently
Guess which leg backs up and how far
Unfortunately the
connection from the
upper left roundabout
to the one in the lower
right doesn’t always
look as open as it is in
the aerial photo
One more project where the roundabout queues every now and then
Luckily the queue
hasn’t started to hurt
the roundabout
further to the east that
is the access point for
a significant new
commercial business
park
Sometimes the queue goes up and around the corner
Even though this
queue is long is it a
“moving” queue and
just like the previous
project, still better
than it was when it
was a signalized
intersection
Since this is already a
2 lane roundabout
any future capacity
improvement will
likely be created by a
metering signal
There isn’t too much further to go to the next roundabout
A substantial limitation to HCS / HCM
6 (in addition to the ones listed in the
image on the right) is that it can only
model up to 4 legs. Does anyone
know of any 5 of 6 legged
intersections?
One last note before I end the
presentation – SIDRA 8 is due out
very soon so please make sure your
COVER (the annual maintenance
contract) is up to date so you get the
new version.
Why not just use HCS software to analyze roundabouts?
Contact Information
Howard McCulloch, PE
NE Roundabouts, Inc.
2396 NY ROUTE 43
Averill Park, New York 12018
Tel: (518) 674-8350
Website: www.roundabouts.cc
E-mail: [email protected]