All About Roundabouts
Roundabouts, rotaries, traffic circles; they are a common sight across most of the world, but less so in North America. In my view, this could be due to several factors. One could be the American street grid development pattern, which had at most four streets meeting at an intersection, rather than more haphazard European village streets. American and Canadian cities also mostly developed post-automobile, when the idea of circular intersections was less desirable for quick car throughput. Finally, as some town subdivision plans strongly discouraged four-way stops in their neighborhoods altogether, there have been fewer opportunities to implement them on local streets.
I will substitute my lack of animation skills with an informative video about the benefits and drawbacks of roundabouts, which I recommend checking out HERE before continuing on.
Modern planning and transportation has gained more insight on the benefits of roundabouts in terms of safety, cleanliness and efficiency. Indeed, the most dangerous places on the road are intersections, where different directions of travel conflict with one another. Without getting too technical, there are only a quarter of the number of potential "conflict points" between cars in a roundabout than there are in a traditional intersection.* A big reason for that is the elimination of the left turn. There is virtually no chance for a high-speed, head-on crash or a broadside crash due to turning traffic in a roundabout. In terms of cleanliness, the throughput of cars without as much idling at a red light can mean fewer emissions, fewer leaked fluids, and less aggressive acceleration out of the intersection, which translates to cleaner air, water and soil. Finally, as mentioned in the video, roundabouts can handle the same traffic volume throughput as a four way intersection, just at a slower and more regular pace. The efficiency of roundabouts can be seen in the increases in safety and decreases in pollution with the same vehicle throughput.
Local Roundabouts (real and fantasy)
Pittsfield and Berkshire County in general don't really have many roundabouts to speak of. The first that probably comes to mind is the new roundabout at Friend Street in Adams. For this project, I will not refer to Park Square as a roundabout, since it is still controlled by traffic signals. Its full circular route was also cut off after a road realignment project there ten or so years ago.
Where else in Pittsfield could roundabouts be placed? I tried my hand at overlying them on the existing intersections at East, Elm and Fourth Street, and at West and West Street (the three-way intersection past the railroad overpass). These intersections were unique because of their complexity, traffic volumes, and potential for conflict with different travel directions. Presented below are some graphical concepts of what these intersections could look like with the roundabout treatment. Please keep in mind these designs are not approved by any transportation engineers, but I did try to keep dimensions as close to the recommended standards as possible.
East Street at Elm Street and Fourth Street. This intersection is one of the more busy and complex in the city, but a well designed roundabout could help to make it more orderly. The odd angles and long signal phases are key characteristics of this intersection. Anyone who has driven, biked, or walked through it has probably seen a car or truck run the red light at one point or another. The double turn lane from Elm Street to East Street toward downtown is also very awkward. As of this year (2017), 25,000 vehicles per day were recorded as passing through East Street near Pittsfield High School.** According to the Federal Highway Administration, that volume could be easily handled by a two-lane roundabout.^
Some benefits of implementing a roundabout here would be a reduction in stacking traffic that backs up to Appleton Avenue and Pittsfield High School, elimination of one travel lane from each direction on East Street, which reduces maintenance, plowing needs, and overall asphalt coverage, and an elimination of traffic signals along with a reduction in speed through the intersection. Along with these, some drawbacks of this plan would be the need to acquire some abutting land for the larger footprint of the intersection, and accommodation of heavier-than-average truck traffic on this route. Overall, though, I believe this change could be a net positive for one of the gateways to downtown, and could also tie in to the planned future roadwork for East Street between Lyman Street and Woodlawn Avenue.
West Street at West Street. A lot of Pittsfield drivers are probably familiar with this intersection, myself being one of them. It is a T-intersection where new West Street rejoins the original West Street after its urban renewal widening fifty or so years ago. The third leg of the intersection leads to the flyovers that intersect Columbus Avenue at Center Street. This intersection is unique because of its very high amount of left turns, and its exceptional width and friendliness to speeding, all while being in one of the most densely populated areas of the city.
I think that a roundabout could be a positive change for this intersection because all left turns would be eliminated. Rather than queuing up, inching forward, and guessing if an oncoming driver from upper West Street is going to go straight or turn right, all traffic would be routed through a single roundabout lane (I am pleasantly surprised at the high usage of directional signals at this intersection, though, based on my empirical observations). As we know, All traffic would flow counterclockwise around the circle, so a driver turning "left" from new West Street would first turn right and then make their way around the circle. Traffic speeds would also be calmed by having to navigate the circle, rather than being able to drive straight through.
Unfortunately there is not as much traffic data available for this intersection since it is not a state route. Though it is safe to estimate that the traffic and truck volumes here are lower than at East Street and Elm Street.
A challenge for this design would be the amount of foot traffic that passes through between neighborhoods and on the way to Big Y or downtown in general. Roundabouts don't really allow for immediate crossing at the intersection itself, but rather an offset crossing away from the circle, where the "splitter island" separates the directions of travel.
Of course, these ideas are just fun thought exercises, and I do not see any indication that projects like these would take place any time in the near future. Some other intersections I had thought of or were suggested by colleagues were the the terminus of Elm Street at Williams Street, and the intersection of Tyler Street/Dalton Avenue/Woodlawn Avenue. What other intersections around town do you think could be ready for a makeover?
** MassDOT data viewer http://mhd.ms2soft.com/tcds/tsearch.asp?loc=Mhd&mod=
^https://www.fhwa.dot.gov/publications/research/safety/00067/00067.pdf [pg. 71]