Roundabouts: A Round Peg in a Square HoleLet’s begin with a scenario that couldoccur in any city or town across the countr... are only three rules for modern roundabouts:1) Traffic moves counterclockwise.2) Entering drive...
Upcoming SlideShare
Loading in …5

Roundabouts: A Round Peg in a Square Hole


Published on

Let’s begin with a scenario that could occur in any city or town across the country. A traditional, four-way intersection on the main road into a municipality’s downtown district has a higher-than-average crash rate, and residents have complained about high traffic speeds. Town leaders hire an engineer to study the problem and recommend a solution. After a comprehensive study, the engineer proposes the intersection be converted into a roundabout. Unfazed by the uncertain looks he receives for his suggestion, the engineer attends a meeting of the Town Council a week later to make his case for the conversion.

  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Roundabouts: A Round Peg in a Square Hole

  1. 1. Roundabouts: A Round Peg in a Square HoleLet’s begin with a scenario that couldoccur in any city or town across the country.A traditional, four-way intersection on themain road into a municipality’s downtowndistrict has a higher-than-average crash rate,and residents have complained about hightraffic speeds. Town leaders hire an engineerto study the problem and recommend asolution. After a comprehensive study,the engineer proposes the intersection beconverted into a roundabout. Unfazed by theuncertain looks he receives for his suggestion,the engineer attends a meeting of the TownCouncil a week later to make his case for theconversion.His report is met with skepticism from somecouncil members and members of the publicin attendance, who make their concernsknown: roundabouts are confusing andunsafe, inconvenient for pedestrians, andexpensive when compared to traditionalintersections. Some even make half-jokingreferences to Clark Griswold (of NationalLampoon’s fame) driving hysterically aroundthe roundabout near Big Ben in London.The engineer explains the accuracy of growingdata in support of roundabouts and how theymoderate vehicle speeds, minimize conflictingvehicle and pedestrian movements, reducethe incidence and severity of crashes, andcan aesthetically enhance an area, whileincreasing road system performance. Thoughacknowledging a roundabout is potentiallymore expensive, the engineer details howthe benefits outweigh the costs and explainsthat some funding programs do exist to coverportions of a roundabout’s construction cost.In the end, the council backs the engineer’sexpertise. A few residents remain concerned,but reserve further judgment. The townbuilds the roundabout, the intersection’ssafety record improves, the speedingcomplaints dwindle, and community membersgrow accustomed to the change – theirsuspicions displaced by acceptance born outof familiarity and performance.Why the resistance? The easy answeris because that is how it’s always been. Wehave grown comfortable with a traffic controlsystem governed by automated signals –third-party referees who tell us when tostop, when to go, and when to yield. Wemotorists don’t even necessarily have tothink that much, we just react; an increasinglydangerous proposition as our roads fill withever more passive and distracted drivers.This tendency to passivity and distraction isespecially hazardous at the most dangerous oftraffic environments, the intersection.The Federal Highway Administration (FHWA)estimates there are 300,000 signalizedintersections in the United States. Aboutone-third of all intersection fatalities occurat these locations, amounting to roughly2,300 people killed each year. Furthermore,ConceptsFishbeck, Thompson, Carr & Huber, Inc.Spring 2013onceptsCDiverging 9Merging 8Crossing 16 33Diverging 4Merging 4Crossing 0 8StandardIntersectionPotential Vehicle Conflict PointsRoundaboutRoundabout Safety Statistics• 38% reduction in all crash severities• 75% reduction in injury crashes• 90% reduction in fatal crashes
  2. 2. are only three rules for modern roundabouts:1) Traffic moves counterclockwise.2) Entering drivers yield to circulating traffic.3) Stay in your lane.This keeps traffic in the circle movingsafely and contributes to a roundabout’scapacity and effectiveness.about 700 people are killed annually inred-light running crashes. It is precisely thisdanger that has given rise to the FHWA’seffort to promote proven safety measures atintersections.Roundabouts are one such measure. TheFHWA says roundabouts have demonstratedsubstantial safety and operational benefitscompared to most other intersection formsand controls, with especially significantreductions in fatal and injury crashes. Inaddition, they can be an effective tool formanaging speed and creating a transitionarea that moves traffic from a high-speed to alow-speed environment.Why are roundabouts safer thantraditional intersections? The one-word answer is geometry. Roundaboutsreduce the number of places one vehiclecan strike another by a factor of four and doaway with the left turn movement againstoncoming traffic (arguably one of the mostdangerous turning movement conflicts,resulting in severe T-bone crashes). Also,since modern roundabouts do not havetraffic signals, they eliminate the scenariowhere a motorist speeds up to beat thered light. Drivers must slow down to entera roundabout because traffic is directedaround a center island, which also serves toreduce vehicle speeds. These lower vehiclespeeds translate to overall intersection safety– the number and severity of crashes dropsdramatically.There is another factor that contributes tothe safety of roundabouts: watchfulness.Drivers tend to be cautious when approachingand driving through a roundabout becauseit does not, initially, feel as comfortable asa signalized or stop-controlled intersection.This feeling can produce a heightenedawareness of our surroundings; the benefitsof which are obvious when compared tothe passive distraction we all witness duringour daily commutes. Roundabouts activelyengage drivers, relying on their ability toassess changing traffic conditions and makereasonable decisions.Significant design elements of aroundabout include a central circulationisland and splitter islands on each approach.Safe pedestrian crossings can be integratedinto the splitter islands. Many roundaboutsare also designed with a truck apron, a raisedsection of pavement around the centralisland that acts as an extra lane for largevehicle turn paths. The back wheels of theoversized vehicle can ride up on the truckapron so the truck can easily complete theturn, while the raised portion of concretediscourages use by smaller vehicles.With a truck apron, roundabouts canaccommodate vehicles of all sizes,including emergency vehicles, buses,farm equipment, and tractor-trailers.The central island can also be designedand landscaped to allow emergencyvehicles to traverse the center in extremeemergencies.Public education is a critical, yet oftenoverlooked, aspect to successful roundaboutimplementation. Many municipalities aresetting aside resources for informationalcampaigns to teach their communities aboutroundabouts. These campaigns includemailings, brochures, online videos, and publicforums.There are few cure-alls when it comes tointersection safety, and roundabouts are notalways the best solution. Some intersections donot have the right characteristics to consider aconversion. However, if designed properly andimplemented effectively, roundabouts offerone of the safest, most efficient, and elegantalternatives to traditional intersection control.Points to ponder the next time you’re stuck atan empty intersection waiting for the signal tochange.Arrows showthe directionof traffic flowApproaching trafficslows and yields totraffic in the circlePedestrians cross atdesignated locationsCirculatoryRoadwayCentral IslandYield LineInscribed CircleDiameterLandscapeBufferTruck ApronEntryExitAccessiblePedestrianCrossingSplitterIslandRoundabouts are easy to useFor more information regarding roundabouts,please contact Chris Sikkema,