Crash prone 'modern roundabouts'

[tradephoric]

A motorcyclist approaching a roundabout suddenly feels like Valentino Rossi... minus the talent:

[kphoger]

I have a cheaper fix =)

I would change very little about these two roundabouts.  The signage is excellent, spelling out which lane is for which street.  And I'm a fan of Alberta striping.  The only two things I would do are...

(1) Extend your suggestion to all points:  remove all solid stripes from within the circulating roadways.
(2) Make all entries and exits the same number of lanes; I believe this helps alleviate drier confusion.

[tradephoric]

I would change very little about these two roundabouts.  The signage is excellent, spelling out which lane is for which street.  And I'm a fan of Alberta striping.  The only two things I would do are...

(1) Extend your suggestion to all points:  remove all solid stripes from within the circulating roadways.
(2) Make all entries and exits the same number of lanes; I believe this helps alleviate drier confusion.

In the Streetview montage posted previously, there are multiple vehicles in the left-hand lane that incorrectly exit at Detroit Ave (the red Camero and the vehicle behind it).  I like your drawing (and am curious about what program you used) but I don't see how this would address this incorrect lane usage problem.  You had said the signage is excellent yet drivers seem to be disregarding it.  It's amazing that a moment in time on streetview captured a wrong way driver and two incorrect lane usages.  I wonder how many mess ups you would see observing the roundabout for a few hours as opposed to looking at a few streetview images. 

[kphoger]

^^  I just use MS Paint, because I'm not tech-savvy.  And I don't think it would address the lane usage problem.  My opinion is that it's been done almost as perfectly as you could do it, yet people are still being stupid.

[tradephoric]

^Thanks.  I use Google Earth to add polygons and paths for my drawings but i find it finicky to work with.  I'll try MS Paint sometime.  I agree that if people are going to disregard the signage that it's hard to design for that.  I personally feel the signage doesn't match the natural instinct drivers have at this roundabout (for whatever reason drivers feel like they should be allowed to exit onto Detroit Ave from the left-most lane). 

[kphoger]

(for whatever reason drivers feel like they should be allowed to exit onto Detroit Ave from the left-most lane). 

I think the geometry of the movement makes it feel like a straight-through movement rather than a turning movement. Two options to correct this:

1) Swing the approach away from center so it meets the roundabout more obliquely, thereby making the right turn more of a right turn.

2) Reduce the diameter of the whole roundabout so all approaches are physically closer to their neighboring exits, thereby highlighting the existence of the roundabout and making that movement feel less like 'staying on the main road:.

[tradephoric]

The 116th Street & Spring Mill Road roundabout in Carmel was originally constructed as a single lane roundabout around 2005.  According to the Carmel Police Department's Annual reports, it never made the top crash locations when it was a single-lane roundabout.  Then in 2013 the roundabout was converted to a 2x2 multi-lane roundabout.  In 2014 the roundabout was the 3rd highest crash location in the city with 51 total crashes.  If you look at historical imagery, the surrounding geometry of the area didn't change much (Spring Mill Road is still 2-lanes north & south of the roundabout and 116th Street is 2-lanes west of the roundabout).  Since there wasn't a significant increase in capacity along the roads surrounding the roundabout, it's hard to argue that there was a significant increase in traffic volumes that would justify the increase in total crashes.  The more likely scenario is that drivers are having more trouble navigating the multi-lane roundabout.




The roundabout at 116th & Spring Mill Road has experienced a significant spike in total crashes since it was converted to a 2x2 multi-lane roundabout a few years ago.  But there are also injury accidents occurring at the roundabout.  Just a few months ago 6 people were injured, 3 critically, when a car crashed at the roundabout:

http://wishtv.com/2016/05/31/police-investigate-serious-one-vehicle-accident-in-carmel/

[tradephoric]

Woodward Avenue in Detroit runs for roughly 27 miles from Pontiac to downtown and is one of the main arterials in the city.  There is a big push for mass transit along Woodward and SEMCOG recently published a 112-page report discussing the rapid transit alternatives being considered.  Included in the report is a list of the most crash prone intersections along the Woodward corridor (there are roughly 70 signalized intersections along Woodward):

http://www.woodwardanalysis.com/pdfs/20150706_woodwardAA_LPA_FINAL.pdf

I thought it would be fun to include a similar comparison for the critical crash roundabouts in Carmel, Indiana.  I couldn't find accurate ADT data for the roundabouts in question so I estimated them all at 35,000 ADT.  The highest capacity roundabouts in America rarely see ADT volumes exceed 50000 and these Carmel roundabouts don't have that much capacity (ie. not one roundabout in Carmel has triple circulating lanes).  Carmel has focused mainly on single-lane roundabouts, which is why the city can spout off their great city wide safety record.  But the fact is the few 2x2 multi-lane roundabouts that have been built in Carmel have not performed very well.  City leaders conveniently ignore this fact.


Notice how the average crash rate at these 2x2 multi-lane roundabouts in Carmel are higher than the intersections along the Woodward corridor?  And if you want to ignore safety for a second and focus entirely on efficiency, let's have a little test.  Someone drive 20 miles along the surface streets of Carmel and I'll drive 20 miles down Woodward and we'll see who gets to their destination first.

[cjw2001]

The 116th Street & Spring Mill Road roundabout in Carmel was originally constructed as a single lane roundabout around 2005.  According to the Carmel Police Department's Annual reports, it never made the top crash locations when it was a single-lane roundabout.  Then in 2013 the roundabout was converted to a 2x2 multi-lane roundabout.  In 2014 the roundabout was the 3rd highest crash location in the city with 51 total crashes.  If you look at historical imagery, the surrounding geometry of the area didn't change much (Spring Mill Road is still 2-lanes north & south of the roundabout and 116th Street is 2-lanes west of the roundabout).  Since there wasn't a significant increase in capacity along the roads surrounding the roundabout, it's hard to argue that there was a significant increase in traffic volumes that would justify the increase in total crashes.  The more likely scenario is that drivers are having more trouble navigating the multi-lane roundabout.




The roundabout at 116th & Spring Mill Road has experienced a significant spike in total crashes since it was converted to a 2x2 multi-lane roundabout a few years ago.  But there are also injury accidents occurring at the roundabout.  Just a few months ago 6 people were injured, 3 critically, when a car crashed at the roundabout:

http://wishtv.com/2016/05/31/police-investigate-serious-one-vehicle-accident-in-carmel/

You've once again quoted a single vehicle incident as a problem with the roundabout.   If an idiot driver in the middle of the night runs off the road at high speed, how is that the roundabout's fault?  If I remember correctly from the news reports at the time this crash was not even in the roundabout - the intersection was simply given in the news story as a nearby reference point.

[kalvado]

The 116th Street & Spring Mill Road roundabout in Carmel was originally constructed as a single lane roundabout around 2005.  According to the Carmel Police Department's Annual reports, it never made the top crash locations when it was a single-lane roundabout.  Then in 2013 the roundabout was converted to a 2x2 multi-lane roundabout.  In 2014 the roundabout was the 3rd highest crash location in the city with 51 total crashes.  If you look at historical imagery, the surrounding geometry of the area didn't change much (Spring Mill Road is still 2-lanes north & south of the roundabout and 116th Street is 2-lanes west of the roundabout).  Since there wasn't a significant increase in capacity along the roads surrounding the roundabout, it's hard to argue that there was a significant increase in traffic volumes that would justify the increase in total crashes.  The more likely scenario is that drivers are having more trouble navigating the multi-lane roundabout.




The roundabout at 116th & Spring Mill Road has experienced a significant spike in total crashes since it was converted to a 2x2 multi-lane roundabout a few years ago.  But there are also injury accidents occurring at the roundabout.  Just a few months ago 6 people were injured, 3 critically, when a car crashed at the roundabout:

http://wishtv.com/2016/05/31/police-investigate-serious-one-vehicle-accident-in-carmel/

You've once again quoted a single vehicle incident as a problem with the roundabout.   If an idiot driver in the middle of the night runs off the road at high speed, how is that the roundabout's fault?  If I remember correctly from the news reports at the time this crash was not even in the roundabout - the intersection was simply given in the news story as a nearby reference point.

Roundabouts require much more attention to the road compared to regular intersection.
And people may be not in their top shape while driving - coming home after long shift, sleepless night, not feeling well etc. It is part of engineer job to design things so that they accommodate imperfect driving. Otherwise, we would have 104" lanes on highway (102" maximum width + whooping 2" clearance on each side). FOr some reason, 12'=144" is a typical value for highway...
So if you cannot design roads safely -  we have some janitor positions open over here, feel free to apply.

[tradephoric]

You've once again quoted a single vehicle incident as a problem with the roundabout.   If an idiot driver in the middle of the night runs off the road at high speed, how is that the roundabout's fault?  If I remember correctly from the news reports at the time this crash was not even in the roundabout - the intersection was simply given in the news story as a nearby reference point.

I quoted that there were 51 total crashes at the 116th & Spring Mill roundabout in 2014.  In 2013 there were 15 or fewer crashes at the roundabout (it didn't rank in the top 20 high crash location in 2013... the 20th highest had 15 crashes).  When total crashes nearly triple from the year prior, you got to scratch your head and ask why.   The likely reason is because the city added a circulating lane at the roundabout and drivers are now having trouble navigating the multi-lane roundabout. 

The 116th & Spring Mill's roundabout is an interesting case study because it's comparing the crash data of the roundabout when it was a single-lane roundabout to the crashes that are occurring now that it's a multi-lane roundabout.  Do you want a roundabout that has 15 crashes a year or one that has 51 crashes a year?  The roundabout currently has an estimated crash rate of 3.99; nearly double what you want to see as a traffic engineer.  The estimated crash rate of the 116th & Keystone roundabout is even worse at over 5.

[tradephoric]

^Put another way, this intersection at Woodward & 10 Mile has fewer total crashes than the roundabout at 116th & Spring Mill Road in Carmel.

[kphoger]

You've once again quoted a single vehicle incident as a problem with the roundabout.   If an idiot driver in the middle of the night runs off the road at high speed, how is that the roundabout's fault?  If I remember correctly from the news reports at the time this crash was not even in the roundabout - the intersection was simply given in the news story as a nearby reference point.

I quoted that there were 51 total crashes at the 116th & Spring Mill roundabout in 2014.  In 2013 there were 15 or fewer crashes at the roundabout (it didn't rank in the top 20 high crash location in 2013... the 20th highest had 15 crashes).  When total crashes nearly triple from the year prior, you got to scratch your head and ask why.   The likely reason is because the city added a circulating lane at the roundabout and drivers are now having trouble navigating the multi-lane roundabout. 

The 116th & Spring Mill's roundabout is an interesting case study because it's comparing the crash data of the roundabout when it was a single-lane roundabout to the crashes that are occurring now that it's a multi-lane roundabout.  Do you want a roundabout that has 15 crashes a year or one that has 51 crashes a year?  The roundabout currently has an estimated crash rate of 3.99; nearly double what you want to see as a traffic engineer.  The estimated crash rate of the 116th & Keystone roundabout is even worse at over 5.

I think the issue is that you used scientific data to compare total crashes, but then you picked a news article to support your analysis of injury crashes.

[tradephoric]

I think the issue is that you used scientific data to compare total crashes, but then you picked a news article to support your analysis of injury crashes.

I don't know of a good resource that breaks down detailed intersection crashes in Carmel by level of injury.  The Carmel Police Department's annual reports only list the total crashes for the top crash locations.  I wish there was a publicly accessible website where you could look up detailed crash information by intersection.  Then independent analysis could be done to support or discredit any reports published by the City of Carmel.  I do know that 3 out of the last 4 fatal crashes in Carmel have occurred at roundabouts.  Keep in mind that there are roughly the same number of traffic signals as there are roundabouts in Carmel; yet 75% of the fatalities over the past few years have happened at Carmel's incredibly "safe" roundabouts. 

[jakeroot]

Keep in mind that there are roughly the same number of traffic signals as there are roundabouts in Carmel; yet 75% of the fatalities over the past few years have happened at Carmel's incredibly "safe" roundabouts.

How much traffic passes through the roundabouts, compared to the signals? I've always maintained that the number of collisions is, more often than not, a factor of the amount of traffic going through the intersection. And to be clear, I'm not suggesting that all busy intersections have high amounts of collisions. It just seems to me that busier intersections have more collisions than quieter ones.

[tradephoric]

I've always maintained that the number of collisions is, more often than not, a factor of the amount of traffic going through the intersection. And to be clear, I'm not suggesting that all busy intersections have high amounts of collisions. It just seems to me that busier intersections have more collisions than quieter ones.

Below is a chart that looks at the average crash rate for different intersection types.  For most intersection types, as the traffic volume (ADT) increases the crash rate decreases.  The old adage "there's safety in numbers"  applies here.  Yes, there will be more total collisions at a busier intersection than a quite one, but the busier intersection will likely have a lower per million entering vehicle crash rate. 

[cjw2001]

Another factor for many of the Carmel roundabouts near US 31 has been 5 years of US 31 reconstruction which has substantially disrupted traffic patterns and pushed more traffic to the local roads over the last several years.   Things are just now returning to normal now that the US 31 project is drawing to a close.

[kphoger]

Keep in mind that there are roughly the same number of traffic signals as there are roundabouts in Carmel; yet 75% of the fatalities over the past few years have happened at Carmel's incredibly "safe" roundabouts.

How much traffic passes through the roundabouts, compared to the signals? I've always maintained that the number of collisions is, more often than not, a factor of the amount of traffic going through the intersection. And to be clear, I'm not suggesting that all busy intersections have high amounts of collisions. It just seems to me that busier intersections have more collisions than quieter ones.

Also, I should point out that 4 is a very small pool to draw conclusions from.

[tradephoric]

Below is an updated list estimating the crash rate of 3x2 and 2x2 multi-lane roundabouts in America.  These multi-lane roundabouts have an average crash rate of 4.09 which is more than double the average crash rate of other intersection types (two lane signalized; undivided signalized; left turn signalized; etc.).  The roundabouts highlighted in yellow have had circulating lanes removed in the roundabout.  The fact that agencies have been actively removing circulating lanes at these complex multi-lane roundabouts is a good indication that there is indeed a crash problem. 

[kphoger]

Below is an updated list estimating the crash rate of 3x2 and 2x2 multi-lane roundabouts in America.  These multi-lane roundabouts have an average crash rate of 4.09 which is more than double the average crash rate of other intersection types (two lane signalized; undivided signalized; left turn signalized; etc.).  The roundabouts highlighted in yellow have had circulating lanes removed in the roundabout.  The fact that agencies have been actively removing circulating lanes at these complex multi-lane roundabouts is a good indication that there is indeed a crash problem. 

It's hard for me to get behind a table like this, when there are obviously multi-lane roundabouts in North America that are not included in the table.  To me, it seems like you're hand-picking the worst multi-lane roundabouts and then using that data to discredit multi-lane roundabouts in general.

[tradephoric]

^^^If what you are saying is true, i wouldn't have included the 68th Avenue & Randall St. roundabout in the analysis since it had a relatively low crash rate.  A crash rate below 2.0 is basically the cut off of being considered an acceptable crash rate in the engineering community.  The reality is i included crash data for every major 2x2 or 3x2 multi-lane roundabout i could find data on.  In any case, this is a public thread.  Anybody who knows of multi-lane roundabouts with low crash rates are welcome to post them here.

[7/8]

I was just reading Waterloo Region's page "All About Roundabouts" and I thought the following picture and video were funny:

[kphoger]

^^^If what you are saying is true, i wouldn't have included the 68th Avenue & Randall St. roundabout in the analysis since it had a relatively low crash rate.  A crash rate below 2.0 is basically the cut of of being considered an acceptable crash rate in the engineering community.  The reality is i included crash data for every major 2x2 or 3x2 multi-lane roundabout i could find data on.  In any case, this is a public thread.  Anybody who knows of multi-lane roundabouts with low crash rates are welcome to post them here.

I'm not savvy enough to know where to find such data.  All I know is that none of the multi-lane roundabouts I've personally driven through or can think of offhand are included.

(Sheridan at Ridgeview in Olathe, KS)
(Branson Landing Blvd at Skaggs in Branson, MO)
(Valley Mills at Robinson in Waco, TX)

Sorry if I offended you, but zero out of three immediately made me think the table was untrustworthy.

[tradephoric]

^^^
The Branson, MO roundabout doesn't have 2 circulating lanes throughout the entire roundabout (one of the leg only has one circulating lane).  This greatly simplifies the turning movements and I would not consider this a true 2x2 multi-lane roundabout. 

The Waco, TX intersection isn't a modern roundabout.  The entry flare angles are way off and there is no pavement marking inside the roundabout. 

The Olathe, KS roundabout is worthy of further investigation.  I just can't find any crash data for it.  If anyone can find detailed crash data for the Sheridan at Ridgeview roundabout it would be greatly appreciated! 

[tradephoric]

A newly constructed roundabout in Port Huron township put a sudden stop to this police chase.  Gotta love how this story preempted the terrifying armed robbery video. 

https://www.youtube.com/watch?v=8aDG1mvkz9Q