Crash prone 'modern roundabouts'

[kphoger]

IIRC, you don't really have a problem with single-lane roundabouts, right?

Obviously I can't speak for tradephoric, but that seems to be what others have said about him, not necessarily what he's stated in so many words.  What he has said is that it seems multi-lane roundabouts generate more frequent and more severe accidents and so he has a problem with them–unless there are steps to be taken to reduce the frequency and severity of those crashes, one of which steps might be restricting the flow of the circulating roadway down to a mix of one and two lanes.  My own reading of tradephoric is that he's willing to base his opinions on what the data suggest, which may or may not fall squarely along the single-/multi-lane divide.

[kalvado]

I can think of at least 4 issues on local divided highways where stripping is apparently flawed- but is not fixed for many years ... simple lines on a pavement.

If it's a minor error, then it's easy for me to imagine it being far down the list of projects.  Basically in the "if money flies through the window" category.

Is daily traffic jam because of that stripping is a good enough reason to move things up the list?

Where the heck are these four places where "simple lines on a pavement" are causing "daily traffic jam"?  Have you brought them up with the appropriate agency?

AT least some of those points were brought up here when people working for local DOT were participating in discussion.
Best response I got (I can look it up, quote is approximate) - departments have a lot of people who counter any change with "it worked for 20 years, why do you want to change it?". That inhibits any meaningful changes.
Why roundabouts do get built in such environment? I don't know; I suspect numbers on the contracts are too attractive - unlike low profile restripping.

[kalvado]

2] in the case of a roadgeek, knowledge comes many years before experience.
3] My age has no bearing on this particular knowledge-based discussion whatsoever.

OK, let's talk knowledge. What can you tell us about roundabouts - beyond what DOT says in driver's manual and advertizing materials?
FOr example, how does throughput of roundabout changes with number of circulating lanes?

[webny99]

Going there not going there. Sorry not sorry.

[kphoger]

2] in the case of a roadgeek, knowledge comes many years before experience.
3] My age has no bearing on this particular knowledge-based discussion whatsoever.

OK, let's talk knowledge. What can you tell us about roundabouts - beyond what DOT says in driver's manual and advertizing materials?
FOr example, how does throughput of roundabout changes with number of circulating lanes?

That doesn't actually negate his statements.  But it doesn't finally get us off the topic of age, at least.

[kalvado]

2] in the case of a roadgeek, knowledge comes many years before experience.
3] My age has no bearing on this particular knowledge-based discussion whatsoever.

OK, let's talk knowledge. What can you tell us about roundabouts - beyond what DOT says in driver's manual and advertizing materials?
FOr example, how does throughput of roundabout changes with number of circulating lanes?

That doesn't actually negate his statements.  But it doesn't finally get us off the topic of age, at least.

Yes, to the questions where roadgeek hobby wouldn't help to find an answer. It is not about counting exits and shaming other drivers, you know...

[tradephoric]

One of the last major roundabouts in Doha, Qatar has been converted to an at-grade signalized intersection.  Looking at historical imagery of Doha, it's quite amazing just how many major-roundabouts have been converted to signalized intersections in a short period of time.  According to Salem Al-Shawai, Assistant Director of the Roads Projects Department at the Public Works Authority, converting roundabouts to signal-controlled intersections has greatly enhances traffic-flow in the city.

https://www.thepeninsulaqatar.com/article/15/06/2017/Qatar-residents-bid-goodbye-to-Sports-Roundabout

The deal with Doha is the roundabouts there were massive.  I remember first encountering Doha roundabouts several years ago when researching if any 3x3 geometry roundabouts in America existed.  While I couldn't find any in America, many examples existed in Doha.  The problem is roundabouts break down when traffic volumes get too high and that is seemingly what happened in Doha (the population went from 500,000 in 2004 to over 1.3 million people today).  The roundabouts simply couldn't handle the influx of traffic.  I'll tell you one thing for sure... Jim Brainard is not the mayor of Doha.

[kalvado]

I'll tell you one thing for sure... Jim Brainard is not the mayor of Doha.

C'mon, a dream situation for any executive/official: first you get funding to build something, run a big project, everyone is happy - jobs, cash flow, visible progress
Then you discover things do not work as expected, get more funding to redo things, everyone is happy again  - jobs, cash flow, visible progress.
Those who pay for it may get upset eventually, but you just need to manage expectations correctly

[tradephoric]

A partial triple-lane roundabout is being proposed in Greenwood, Indiana.  The  roundabout at Madison Ave & Smith Valley Road will be about 250 feet from the traffic signal at Smith Valley Road and US 31 (roundabout traffic will routinely queue up through the US31 signal).  Even in the model pictured you have a queue of cars at the roundabout with US31 SBLT traffic being released into the queue... rear end accidents anyone?  Here is a link to the public open house presentation given.  In it they state that roundabouts reduce total crashes by 44% compared to traditional intersections.  Crashes are more likely to increase 444% if this triple-lane roundabout is built, but whatever.  By then it will be built and the promises of how well this roundabout will work will be forgotten.


http://www.greenwood.in.gov/egov/documents/1512413834_41847.pdf

[jeffandnicole]

A partial triple-lane roundabout is being proposed in Greenwood, Indiana.  The  roundabout at Madison Ave & Smith Valley Road will be about 250 feet from the traffic signal at Smith Valley Road and US 31 (roundabout traffic will routinely queue up through the US31 signal).  Even in the model pictured you have a queue of cars at the roundabout with US31 SBLT traffic being released into the queue... rear end accidents anyone?  Here is a link to the public open house presentation given.  In it they state that roundabouts reduce total crashes by 44% compared to traditional intersections.  Crashes are more likely to increase 444% if this triple-lane roundabout is built, but whatever.  By then it will be built and the promises of how well this roundabout will work will be forgotten.


http://www.greenwood.in.gov/egov/documents/1512413834_41847.pdf

I see traffic stopped at 3 out of the 4 legs of the standard intersection.  Rear end accidents anyone?

[kalvado]

A partial triple-lane roundabout is being proposed in Greenwood, Indiana.  The  roundabout at Madison Ave & Smith Valley Road will be about 250 feet from the traffic signal at Smith Valley Road and US 31 (roundabout traffic will routinely queue up through the US31 signal).  Even in the model pictured you have a queue of cars at the roundabout with US31 SBLT traffic being released into the queue... rear end accidents anyone?  Here is a link to the public open house presentation given.  In it they state that roundabouts reduce total crashes by 44% compared to traditional intersections.  Crashes are more likely to increase 444% if this triple-lane roundabout is built, but whatever.  By then it will be built and the promises of how well this roundabout will work will be forgotten.

I see traffic stopped at 3 out of the 4 legs of the standard intersection.  Rear end accidents anyone?

You know, that is one of the things that causes concerns when red light cameras are installed. Managing the expectations. I am fairly used to waiting in line at roundabout entry, but that is not what is advertised as the way they operate.

[tradephoric]

Considering that no triple lane roundabout built in America has ever seen a reduction in crashes, it's laughable to think that the Greenwood roundabout is going to be the first one that does.  A recent triple lane roundabout at 14 Mile & Orchard Lake was built about 200 feet from a signalized intersection in Michigan.  It had the most crashes in the entire state of Michigan last year.  You really think Indiana drivers are going to flow through this roundabout just fine?   Yep J&N, just rip on how bad Michigan drivers are then... until there are like 130 crashes at that Indiana roundabout when the year before the roundabout there was like 13.  Yep, Indiana drivers are great.

[kphoger]

The  roundabout ... will be about 250 feet from the traffic signal ...

Yuck.  No.  Bad.

[jeffandnicole]

Also...how many at-grade jughandles are in Indiana, such as the one in the graphic above?  That in itself is a learning experience for those that want to turn left, but need to from the right lane.

[cjw2001]

The  roundabout ... will be about 250 feet from the traffic signal ...

Yuck.  No.  Bad.

And the existing traffic signal being replaced is the same distance away.  Traffic isn't suddenly going to backup in greater numbers by replacing one intersection type with another.

I drive through this intersection a few times a year when I go to my car dealer.   There is much more turning traffic than thru traffic at this intersection, and a roundabout should be an improvement for turning traffic vs the current intersection.

Also the diagram posted by trade doesn't show the additional connectivity to US 31 just to the south.  A good portion of the volume through this intersection is either coming from or going to the intersection of Madison Ave with US 31 further south:  https://www.google.com/maps/@39.6056363,-86.1070826,321m/data=!3m1!1e3    Due to all the turning traffic coming from or going to the intersection to the south the short segment between US 31 and Madison on Smith Valley has lower traffic volume.

[cjw2001]

Yep, Indiana drivers are great.

Feel free to make a field trip to Carmel and watch the experienced Indiana drivers navigating over 105 roundabouts with ease on a daily basis.

[jakeroot]

I can tell by the setup that the Greenwood roundabout will likely need box markings to prevent blocking. Doesn't mean it's a bad place for a roundabout, though.

Will any city build a signalised roundabout at some point?

[webny99]

Will any city build a signalised roundabout at some point?

I think that's called a traffic circle 

[kj3400]

Will any city build a signalised roundabout at some point?

I think that's called a traffic circle 

The UK's signalized roundabouts would like to have a word.

[Brian556]

I can tell by the setup that the Greenwood roundabout will likely need box markings to prevent blocking. Doesn't mean it's a bad place for a roundabout, though.

Will any city build a signalised roundabout at some point?

There is one. Columbus Cir in NYC

[jakeroot]

I can tell by the setup that the Greenwood roundabout will likely need box markings to prevent blocking. Doesn't mean it's a bad place for a roundabout, though.

Will any city build a signalised roundabout at some point?

There is one. Columbus Cir in NYC

That's more of a signalised traffic circle. I'm talking about a roundabout laid out in a "modern roundabout" way with deflection and whatnot, but with signals.

Carmel's metered roundabouts along the Keystone Parkway are sort of up this alley, but aren't quite fully signalised.

[tradephoric]

The  roundabout ... will be about 250 feet from the traffic signal ...

Yuck.  No.  Bad.

And the existing traffic signal being replaced is the same distance away.  Traffic isn't suddenly going to backup in greater numbers by replacing one intersection type with another.

You are ignoring the fact that closely spaced traffic signals can be coordinated so that the main platoon clears both intersections.  You lose that coordination when one of the signals is converted to a roundabout.  CJW, you really can't see the potential of EB Smith Valley Road traffic backing up through the U.S. 31 intersection once the roundabout is complete?   A triple-lane roundabout within 250 feet of a major signalized intersection along U.S. 31.... I don't care how you want to spin it... that's no bueno.

[kphoger]

The  roundabout ... will be about 250 feet from the traffic signal ...

Yuck.  No.  Bad.

And the existing traffic signal being replaced is the same distance away.  Traffic isn't suddenly going to backup in greater numbers by replacing one intersection type with another.

You are ignoring the fact that closely spaced traffic signals can be coordinated so that the main platoon clears both intersections.  You lose that coordination when one of the signals is converted to a roundabout.

↑  Exactly.  No possibility of coordination.

[cjw2001]

The  roundabout ... will be about 250 feet from the traffic signal ...

Yuck.  No.  Bad.

And the existing traffic signal being replaced is the same distance away.  Traffic isn't suddenly going to backup in greater numbers by replacing one intersection type with another.

You are ignoring the fact that closely spaced traffic signals can be coordinated so that the main platoon clears both intersections.  You lose that coordination when one of the signals is converted to a roundabout.  CJW, you really can't see the potential of EB Smith Valley Road traffic backing up through the U.S. 31 intersection once the roundabout is complete?   A triple-lane roundabout within 250 feet of a major signalized intersection along U.S. 31.... I don't care how you want to spin it... that's no bueno.

I understand the concern, I just don't believe the traffic is that heavy on that short east/west segment.   There is far more traffic turning onto US 31 north or south than there is crossing US 31.  Now I could be wrong as my personal experience is limited to making trips on Smith Valley through that area only a few times each year (usually during weekday traffic), but every time I've been in that area there has been no signs of heavy east/west traffic on that short segment.  Southbound traffic on US 31 has minimal reason to turn left as that route would soon take them back north (the direction they came from).  Northbound traffic on US 31 has virtually no reason to turn right on Smith Valley as anyone that wants to go east has already turned off at the Madison intersection just to the south and would approach the roundabout from the south and not the east.   That leaves only what limited eastbound traffic would be crossing US 31 on Smith Valley and I simply don't expect much volume there.

For westbound traffic on Smith Valley, most traffic turns left on Madison to get to US 31 southbound via the next intersection to the south, they don't go straight to turn left on US 31.  There is minimal traffic that continues on Smith Valley with the intention to cross US 31.

I don't have actual traffic counts but would expect that the engineers did have that info and took it into account before deciding on this design.

[kalvado]

The  roundabout ... will be about 250 feet from the traffic signal ...

Yuck.  No.  Bad.

And the existing traffic signal being replaced is the same distance away.  Traffic isn't suddenly going to backup in greater numbers by replacing one intersection type with another.

You are ignoring the fact that closely spaced traffic signals can be coordinated so that the main platoon clears both intersections.  You lose that coordination when one of the signals is converted to a roundabout.  CJW, you really can't see the potential of EB Smith Valley Road traffic backing up through the U.S. 31 intersection once the roundabout is complete?   A triple-lane roundabout within 250 feet of a major signalized intersection along U.S. 31.... I don't care how you want to spin it... that's no bueno.

I understand the concern, I just don't believe the traffic is that heavy on that short east/west segment.   There is far more traffic turning onto US 31 north or south than there is crossing US 31.  Now I could be wrong as my personal experience is limited to making trips on Smith Valley through that area only a few times each year (usually during weekday traffic), but every time I've been in that area there has been no signs of heavy east/west traffic on that short segment.  Southbound traffic on US 31 has minimal reason to turn left as that route would soon take them back north (the direction they came from).  Northbound traffic on US 31 has virtually no reason to turn right on Smith Valley as anyone that wants to go east has already turned off at the Madison intersection just to the south and would approach the roundabout from the south and not the east.   That leaves only what limited eastbound traffic would be crossing US 31 on Smith Valley and I simply don't expect much volume there.

For westbound traffic on Smith Valley, most traffic turns left on Madison to get to US 31 southbound via the next intersection to the south, they don't go straight to turn left on US 31.  There is minimal traffic that continues on Smith Valley with the intention to cross US 31.

I don't have actual traffic counts but would expect that the engineers did have that info and took it into account before deciding on this design.

There is no data for that specific segment; 27.5 and 36k on US 31 north and south of intersection respectively; 14 and 19 on Smith Valley and 17k on Madison.
Seems like there is a good chunk of local traffic..
http://indot.ms2soft.com/tcds/tsearch.asp?loc=Indot&mod=