> Big snowstorms tend to reveal huge swaths of public space that drivers simply don't use — they appear as piles of snow and show us all exactly where neckdowns could easily be built. Hence, #sneckdown.
#trafficEngineering #stuffInTheStreet #Bollards
#TrafficEngineering
One knows when one has watched too many #TrafficEngineering videos on YouTube when:
Re-watching #TheWizardOfOz movie today, I spotted that there are two roads leading from Munchkin City: the Yellow and Red Brick Roads. They terminate at a central gyratory.
But the intersection, like much road design, was clearly engineered for more exits than ended up being built, but now cannot be expanded according to the original plan. The Yellow and Red Brick roads don't end at diametrically opposite sides of the central circle, but actually quite close to each other on the circumference. Moreover, there's no room to put in the other 5 or so Brick Roads that there is space for on that circle.
There are some motorway and A road roundabouts like that in my neck of the woods, with phantom exits or spaces for (say) planned flyovers that never got built.
It's worth noting that the Yellow and Red Brick roads never actually meet.
American and Canadian Cities with the Most Roundabouts – UPDATE #2
Guest post by Dan T. – Thank you, Dan!
[Note: To most people, the terms traffic circle, rotary, and roundabout are synonyms, but not to traffic engineers. Engineers usetraffic circle as a generic term for all circular intersections, while rotaries and roundabouts (sometimes modern roundabouts) are subsets that have specific features as discussed in the article. This article will use the traffic engineers’ definitions.]
Roundabout in Carmel, IN – Source: eri.iu.eduTraffic engineers love roundabouts. These circular intersections do several things to make traffic better. They cause drivers to slow down, but without forcing them to a complete stop, at least not all the time. They reduce the number of conflict points in an intersection. And where those conflict points do occur, the traffic is intersecting at a shallow angle, rather than a right angle as at traditional intersections. All these drastically reduce the number of serious accidents where injuries or fatalities result.
Circular intersections have a long history. For example, Columbus Circle (which is by no means the first one) in New York was first formed about 1870, although it didn’t get its name until the 1890s when the statue of Columbus was erected. In those horse-and-buggy days, people went around the circle both directions. In 1905, William Phelps Eno, a proto-traffic
engineer, suggested that all the traffic in Columbus Circle should go around the same direction. This was a step towards the modern roundabout, but there were more steps to be made. (Columbus Circle, by the way, is classified by traffic engineers as a signalized traffic
circle and not a roundabout. Modern roundabouts do not have signals.)
The earliest traffic circles had the legs meeting the circle at right angle intersections. They also often had parking allowed along the circular road and allowed pedestrians to access the central island. Some even had buildings in the center. These features didn’t do much to
improve traffic, so during the 1930s, the rotary was developed.
Rotaries are large (some as much as 600 feet across) and initially had no traffic controls. The nearside priority rule, where drivers yield to a vehicle coming from the right, was the most common rule. This meant that vehicles within the circle had to yield to incoming vehicles. Under heavy traffic, this resulted in gridlock. When traffic control signage was installed, they were often designed to speed traffic between two of the legs. Those two approaches had no stop or yield signs as they entered, the traffic already in the circle had to yield to them. Again, gridlock would occur under heavy traffic loads.
Source: co.washington.mn.usThe incoming lanes of rotatries were angled so they met the circle at close to a perfect tangent, but then the incoming vehicles would have to change lanes to get in the circle. The traffic would not be expected to slow down at all, but then have to change lanes again to exit. The high speeds (as much as 40 mph) and lane changes tended to cause serious
accidents. Because of the gridlock and high accident rate, rotaries lost favor in the US in the mid-1950s.
The modern roundabout was developed in Britain in 1966 by Frank Blackmore. The big improvement was that the traffic already in the circle always gets the right-of-way (offside priority rule) and anyone trying to enter it should yield to them. They also are smaller and
require drivers to slow down. Further refinements have been made over the years: the shape of the splitter islands was optimized to angle the incoming traffic in the right direction while still giving drivers a good view of the traffic they must yield to, truck aprons provide for
large vehicles to use them, and subtle curves in the incoming lanes as well as the final curve at the splitter island slow the incoming traffic.
The UK and western Europe in general quickly adopted modern roundabouts and now there’s well in excess of 100,000 there. The US and Canada were slow to adopt the modern roundabout. Traffic circles still had the bad reputation, so even the improved version from Britain was not looked on favorably. The first two modern roundabouts in the US were not built until 1990. Those two were in Summerlin, Nevada, a planned community in Las Vegas. Following that, there was a very slow adoption in the rest of the country. By the turn of the century, there were still only a couple hundred in the entire US. They started to take off in the oughts to the point where there are now about 8,000 with 450 to 500 new ones being built every year.
The following list is based on an extensive database of circular intersections maintained by Kittelson and Associates, an engineering firm based in Portland OR (see the link at the end of the article). The entries in the database are divided into five categories: Roundabouts,
Rotaries, Traffic Calming Circles, Signalized Circles, and Other. The counts in the lists below are only of Roundabouts, and not of the other categories.
[Note: Kittelson doesn’t make any money from hosting the database and all the entries are contributed by volunteers. If you know of a roundabout not in the database, feel free to submit it for inclusion.]
Source: carmel.in.govThe city with the most roundabouts (possibly the most in the entire world) is Carmel, Indiana, a suburb of Indianapolis. In the late 1990s, their mayor, James Brainard, who’d learned of them at school in England, started pushing the city to replace all of its traffic lights with roundabouts. The Kittelson database contains all of them, but some are classified as Other for various reasons. Several allow pedestrian access to the central island, some do not have splitter islands, one has parking along the circular roadway. The counts in this list are only of those classified as Roundabouts in the database.
- Carmel IN = 155 – updated 8/5/25
- Colorado Springs CO = 61
- Columbia MO = 55 – updated 12/9/25 – thank you, Cindy!
- Loveland CO = 47
- Austin TX = 47 – updated 8/5/25 – thank you, J. Lee!
- Frisco TX = 45
- Charlotte NC = 44
- Lincoln NE = 43
- Bend OR = 42
- Durham NC = 37
- Raleigh NC = 37
- Las Vegas NV = 37
- Fort Worth TX = 35
- Omaha NE = 35
- Noblesville IN = 34
- Kansas City MO = 33
- The Villages FL = 32
- Miami FL = 31
- Conway AR = 29
- Fishers IN = 28
- Sarasota FL = 27
- Howard WI = 25
- Ladera Ranch CA = 25
- Lenexa KS = 25
- Kennewick WA = 24
- Lawrence KS = 24
- Chattanooga TN = 23
- El Paso TX = 23
- Westfield IN = 23
- Dublin OH = 22
- McKinney TX = 22
- Tallahassee FL = 22
- Mount Pleasant SC = 21
- Toledo OH = 21
- Billings MT = 20
- Gainesville FL = 20
- Wilmington NC = 20 – added 3/21/22
- Woodbury MN = 20
- Cary NC = 19
- De Pere WI = 19 – added 3/21/22
- Fort Wayne IN = 19
- Olathe KS = 19
- Reno NV = 19
- Anchorage AK = 18 – added 3/21/22
- Brighton CO = 18
- Columbus GA = 18
- Lacey WA = 18
- Neenah WI = 18
- Olympia WA = 18
- Roseville CA = 18
- St George UT = 18
- Santa Fe NM = 18
- Spokane WA = 18
- West Jordan UT = 18
- Jacksonville FL = 17 – added 3/21/22
- Orlando FL = 17
- Oxford MS = 17 – added 3/21/22
- Tampa FL = 17
- Topeka KS = 17
- Wake Forest NC = 17
- Alpharetta GA = 16
- Grand Junction CO = 16
- Indianapolis IN = 16
- Madison WI = 16
- Modesto CA = 16
- Overland Park KS = 16
- Appleton WI = 15
- Jacksonville FL = 15
- Lee’s Summit MO = 15
- Scottsdale AZ = 15
Canada similarly got off to a slow start in building modern roundabouts.The first was built in Montreal in 1998. But they also took off in the oughts (2000-2009) and now there’s over 1000 in the entire country, with 60 or 70 new ones every year.
- Calgary AB = 55
- Ottawa ON = 51
- Winnipeg MB = 47
- Lethbridge AB = 29 – added 3/21/22
- Cambridge ON = 25
- Kitchener ON = 21
- Waterloo ON = 20
- Kelowna BC = 17
- Whitchurch-Stouffville ON = 14
- Markham ON = 13
- London ON = 12
- Milton ON = 12
- Victoria BC = 12
- Aurora ON = 11
- Gatineau QC = 11 – added 3/21/22
- St John’s NL = 11
- Saskatoon SK= 11
- Surrey BC = 11
- Terrebonne QC = 11
- Sherbrooke QC = 10
- Richmond Hill ON = 9 – added 3/21/22
- Whitehorse YT =9 – added 3/21/22
- Windsor ON = 9
- Charlottetown PE = 8
- Chilliwack BC = 8
- Hamilton ON = 8
- Saguenay QC = 8
- St Thomas ON = 8
- West Kelowna BC = 8
[Note: When submitting a new roundabout to the Kittelson database, the city name provided by the software is actually the name of the post office that serves where the roundabout is. While that can be changed by the submitter, it usually is not. What this means is that many cities get credit for roundabouts outside their city limits. Unfortunately there’s no simple way to fix this, so the city counts above are not perfectly accurate.]
SOURCES:
- https://roundabouts.kittelson.com/ Kittelson’s database
- https://www.carmel.in.gov/department-services/engineering/roundabouts – Carmel’s roundabout page, which has a link to a map of all Carmel’s roundabouts.
- How Stuff Works: Roundabouts – https://science.howstuffworks.com/engineering/civil/roundabouts.htm
- A HISTORY OF ROUNDABOUTS IN THE UNITED STATES AND FRANCE – https://babel.hathitrust.org/cgi/pt?id=mdp.39015023846507&view=1up&seq=629
- Personal knowledge
- https://www.carmel.in.gov/home/showpublisheddocument/22960/638775633694530000
#carmel #highways #indiana #planning #roadsStreets #rotaries #roundabouts #traffic #trafficCircles #trafficEngineering #transportationEngineering
#trafficEngineering is a social science not technical profession and if we're not going to hold the Engineer of Record accountable for #trafficViolence, then they should not hold any authority over street design. #visionZero
Video: crossing the #DivergingDiamond on a bike. In the first crossing you have right of way, and the rest of the time you're told to wait even while the parallel green lights protect you with a wall of traffic. Don't miss the scofflaw driver rolling the red light at the end. Note that you cannot cross to/from the other side of the street, so this dance to get into the center is stupid, why not just be crossing only 2 single ramp lanes? #BikeTooter #TrafficEngineering #DriverAccountability
Combining short-trip data with #levelOfTrafficStress to identify areas that could shift the most trips onto bikes by investing in #protectedBikeLanes and other infrastructure #BikeTooter #trafficEngineering #bollards #climateAction #stuffInTheStreet #JFDI
102nd, Glisan, 122nd Ave. Known for being deadly streets. Three unarmored people killed with cars in one night. These are #crashNotAccident #trafficEngineering Design Failure, #ZeroVision. Slow down, turn your lights on, get your city to install #bollards and #stuffInTheStreet #VisionZero #Portland #pdxBikes
Are you wondering how to take CAVs into account when developing airport landside traffic flow simulations? 🤔 We got you covered! 😉 Find our guidance at this link: https://nap.nationalacademies.org/read/28600/chapter/22. 🚗 Then read our Philly application example: https://nap.nationalacademies.org/read/28600/chapter/8. ✈️
#airports #engineering #planning #trafficengineering #transportation #stem
Are these fir trees #dendrology #BikeLaneSweeper #trafficEngineering #paintIsNotProtection #fossilFools
What's really nuts is: they don't just let me paint the lanes. Tell me the functional difference between a painted line and some meat occupying a space? [I stopped at ~1min here because somebody lost their sweatpants in the street. (yes that's a bracket, not a parenthetical)] #BikeLaneSweeper #pdxBikes #ClimateAction #resist #HorseChestnuts #punctuation
Follow me for more #trafficEngineering / #philosophy tips.
shunning drivers for their behavior << bending their cars with infrastructure if they're not careful enough #trafficEngineering #bollards #FuckCars
I'm almost never there in a car but the two-lanes offset part of Hawthorne at 12th is so stupid, just don't. Somebody about crashed into me in the left lane, crossing the solid line because they didn't think both lanes turn left, then we get around the corner and in fact the left lane is parked cars not thru traffic 🙃 #trafficEngineering brainworms
How much of the settlement is PBOT+TriMet paying? How much the country club? Also note the city renews the liquor/beer license of every business once a year, regardless of the availability or quality of bike parking or surplus of car parking and lack of bike infrastructure at the location. ffs [and also fuck the O] https://archive.is/LZxzu#selection-223.0-226.0 "claims against the club and local governments were dismissed without money changing hands"
#trafficEngineering is not a profession, #BanCars ban #stroads
Checking the video, I suppose the operator may have been focused on policing the SUV driver who was already in the process of figuring out what the infrastructure failed to tell them. #ACAB #honky #trafficEngineering
The intersection of Garden City Road and Granville Avenue in Richmond has to be one of the most confusing, hostile, and wasteful of space intersections in Metro Vancouver.
#TrafficEngineering #probability #distraction
Does anyone know of research quantifying the risk related to information potentially pulling drivers' eyes off the highway? I believe I've seen research on billboards, but those may be out of the control of the road planners. However, dynamic signs on highway overpasses warning fast-moving drivers of slowdowns are eye magnets, but short; ditto "DUI enforcement" or "Click it or tick 't" notices. In each of those cases, I'm not concerned about the distraction. Then there are, for example, silver alerts. I generally don't have enough time to read these at highway speeds, because they're information-dense. Has anyone performed the calculus? Do departments posting these have reason to be confident that the probability of at least one crash caused by distraction multiplied by the human and financial and disruptive cost of a crash--that's one side of the equation-- lower than the benefit of reporting the wandering somehow-incompetent driver?
The riding-your-bike-somewhere to firing-traffic-engineers pipeline is so very fucking short, I know people aren't riding their bikes enough. #FuckCars #BanCars #trafficEngineering #defundDOTs #BikeTooter
"at first I was annoyed by the bikes, but when I was still recovering from a broken foot, I tried those rental Metro bikes and was like, "Oh hell no to riding on Wilshire..."
https://bsky.app/profile/cranemonster.bsky.social/post/3lsuw3lh6os2i
CYCLISTS DISMOUNT as a road design failure
https://bettercolumbia.ca/2025/06/27/dear-engineers-stop-making-cyclists-dismount/
We need to hold traffic engineers who design this dangerous mess responsible for the deaths. Their decades old guidebooks are filled with approaches that put safety LAST.
😞 Constant warning bells for no reason and bike-shaped traffic lights nobody pays any attention to because most of the time they are telling you to wait forever while nobody goes by. The train alarms come down like 45s before the max or sometimes they're down for a stopped heavy rail train that blocks the crossing for hours... #VisionZero #ZeroVision #trafficEngineering #transit #pdxBikes SE 8th near Division
oregonlive.com/portland/2025/06/max-train-strikes-kills-person-in-se-portland.html
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