How Does SIDRA

Incorporate the HCM

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

How does HCM 6 compare to previous DOTD runs – 165 @ Pinecrest

How does HCM 6 compare to previous DOTD runs – US 171 @ LA 1212

How does HCM 6 compare to previous DOTD runs – LA 447 @ I-12

How does HCM 6 compare to previous DOTD runs – Hooper @ Sullivan

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: round@roundabouts.cc

Thanks to everyone

here this morning and to

LTRC / DOTD for allowing

me to be a part of this

wonderful conference