Most people have heard of or seen a traffic circle or roundabout before, but it might be fair to say that you haven’t heard of a traffic peanut. It is one of the latest traffic calming devices to hit the road.

To best appreciate what a traffic peanut is, it is important to understand the distinctions between the traffic circle and the roundabout. While roundabouts and traffic circles appear to be indistinguishable at first glance—by allowing vehicles to flow continuously in a circle—they serve traffic by different means. Robson Forensic recognizes three major distinctions between traffic circles and roundabouts:

  1. Yield: Firstly, rather than having circulating traffic yield to entering vehicles, roundabouts require that entering vehicles yield until there is an opening in traffic.1
  2. Speed: There is a difference in traffic speeds. The traffic circle is typically much larger in diameter which allows cars to travel at higher speeds. The roundabout is smaller in diameter, forcing cars to slow down.
  3. Geometry: By adjusting the geometry at the mouth of the splitter island, center island and exit, vehicles entering the roundabout are safely deflected by on-going traffic.1 The free flow of traffic offers faster travel times despite reduced vehicle speeds.1 In fact, the reduced speeds and increased driver caution create a safer bicyclist and pedestrian environment. “[Traffic circle’s] 10-14 foot crosswalk, from curb to splitter island, exposes slow-walking seniors to motor vehicles for less time than most conventional intersections.”3

One city in Indiana has taken the idea of roundabouts and ran with it. The city notes that they have witnessed a significant decrease in traffic crashes since installinh over 120 roundabouts throughout Carmel, IN since 1996.4 Roundabouts have proven to be the superior solution to traffic interactions in Carmel. This is even more prevalent when taking into account that installing and maintaining a roundabout is essentially a one-time cost. Installing signals and traffic crossing lights cost up to $300,000 and that doesn’t include maintenance fees and electricity costs. A lack of reliance on electricity reduces the intersections footprint further as well as allows it to be functional even during emergencies like power outages.

With all the benefits that roundabouts provide, they tend to be a popular solution for fixing dangerous intersections. Unfortunately, not all intersections can accommodate the correct geometries for a successful roundabout. For example, rather than intersecting at right angles, some roads meet and create two narrow and two wide wedges. Perhaps one of the roads does not meet at the center causing an awkward gap in the intersection or several different roads intersect at obscure angles. In order to solve issues like this the traffic peanut was created. Despite being similar in size to a traffic circle, the traffic peanut operates like a roundabout. The peanut like shape is created by conjoining two roundabouts. Traffic is then allowed to freely flow around the elongated shape.5 In addition to this, the pinched shape at the center allows for a pedestrian path that was previously unobtainable. As a bonus by virtually eliminating the need to stop and accelerate, fuel usage is reduced which lessens the amount of pollutants emitted by vehicles.

Three noteworthy case studies explored below are: Inman Square in Cambridge, MA, Kelly Square in Worcester Massachusetts, and an intersection in Beech Grove, IN. All of these intersections have slightly different circumstances that make them unsafe for both vehicles and pedestrians alike. The two Massachusetts intersections were especially difficult for pedestrians to navigate. The current geometry of the intersections forces pedestrians to walk through crosswalks that are much longer than intersections at right angle. In Worcester, MassDOT released a  a rough graphic representation of the traffic peanut in 2019.6 After considering public input, the design was refined and a yearlong construction project was initiated in November 2019.7 Unlike the previous two examples Beech Grove is a relatively suburban area. Kittelson & Associates, the firm proposing the traffic peanut in Cambridge, claims that the traffic peanut is a “safer, stress-free intersection for all.”5  Their design incorporates new open/green space, protected bike lanes, and shorter pedestrian crossing distances. At rural intersections such as this, drivers are forced to drive up perpendicular to the road, which provides drivers with greater visibility of oncoming traffic. Some drivers do not follow this rule and in a need for speed choose to drive straight, regardless of their limited vision. Local government and law-enforcement have been working diligently to secure funding to implement a traffic peanut at the intersection of Perkins and Churchman Avenue. The proposed idea for this intersection differs greatly from the first two because they plan to implement a fully functional roundabout at one end of the peanut. This is in an effort to supplement the intersection of a third road, East Southern Ave, near the site. GAI Consultants’ Brian Craig, the project manager, attributes public and private collaborations to making the traffic peanut become a reality in the near future.8 Although all of these traffic peanut examples have yet to be complete, the projects pose a flexible solution for allowing vehicles, bicyclists, and pedestrians to coexist.


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