Traffic Roundabouts

Appraisal of the ideas offered below in “Traffic / Traffic Insights…” suggests there is plenty of evidence a new traffic signal or additional stop signs at the Hamakua/Aoloa intersection may well not be the best solution for vehicles or pedestrians.

The Hamakua/Aoloa intersection is one of the two mauka corners of Kailua Town and is effectively the beginning of business activity along Hamakua Drive. It is the point of transition between the open streetscape of the Kawainui Stream bridge and the pedestrian rich retail section of Hamakua.

Long range the City & County might consider incrementally upgrading Hamakua between Aoloa and Hekili Streets into a length of more mutual traffic use between cars and pedestrians (on foot or bike, skateboard, wheelchair, etc.) Guided by the demonstrated cost saving effectiveness of the passive measures described in the “Traffic / Traffic Insights…” menu item, that Hamakua traffic landscape could be reconfigured to function more as a “public realm” providing 1) busy residents and visitors a more welcoming sense of engagement, and 2) the Hamakua Marsh merchants the resulting broader clientele.

Cairns opens his “Traffic / Traffic Insights…” article with an delineation of the logic underlying the creation of these “shared spaces”. He, and others on the list, then go on to effectively explain with examples how these principles have been successfully applied to resolve modern traffic management problems.

Once the motorist is within such a successfully managed traffic area, the chain of driver uncertainty > peaked attention > engaged intellect > common speed reduction, helps to support the community safety goal.

But first. The overriding traffic issue around the Hamakua/Aoloa intersection is the lack of prudent driver speed on Hamakua. Given the intersection’s transitional status it’s no surprise there’s a speeding issue. We’ve learned those speeds are not a function of posted speed limits. Drivers are apparently driving as fast as they feel safe for their own well-being.

mphvsinjury|NCHRP2Ed…from “Literature Review on Vehicle Travel Speeds and Pedestrian Injuries.” Final Report DOT HS 809 021. National Highway Traffic Safety Administration, Washington, D.C., 1999.

Screen Shot 2015-11-26 at 7.49.22 pm

…from “Model Design Manual for Living Streets.”, Los Angles County, 2011.

These two charts document the results of how vehicle speed affects the severity of human injury. These are the speeds pedestrians face at the Hamakua/Aoloa intersection. Mitigating our current traffic speeds would dramatically affect the extent of pedestrian injury.

What methods beyond signage can be used to cause motorists to slow down through the intersection?

The location of the Hamakua/Aoloa intersection is at the border of Kailua retail activity and the commuter track to and from Enchanted Lake. In addition to proven passive management measures, effective traffic calming at that point would require, in my estimation, additional physical structure to slow speeders headed in, or out of Kailua Town.

The horizontal traffic deflection provided by a Roundabout, with a single circulating lane, would so moderate that intersection traffic. In fact it has been suggested a Roundabout on Hamakua at both the Aoloa and Hahani intersections would even better provide the calming of through traffic on which successful shared spaces depend.

All four roundabout inlets would equally share access to the circle. All stop signs would be replaced with yield signs allowing a fluid, near continuous traffic movement for all participants. This constant movement of all traffic vs. the stop/start of signs and signals is the key to how roundabouts improve flow capacity even at lower speeds, i.e., the speeds necessary for safety. …Win/Win.

The benefits of roundabouts include:

  • increased pedestrian and vehicular safety
  • greater comparative traffic flows
  • decreased fuel consumption, air pollution and vehicle operating costs
  • noise abatement due to slower, smoother traffic with fewer decelerations and accelerations
  • comparable infrastructure and maintenance costs
  • increased natural beauty with greater opportunity for landscaping
  • encouragement of healthful walking and cycling
  • increased business activity and opportunity
  • see a more comprehensive listing in the FAQs

These two links each provide brief US histories with Roundabouts, the second includes some international comparisons.

Don’t Be So Square
The Case for More Traffic Roundabouts

“Roundabouts are also far safer than traffic signals, cause less delay, and have more capacity. They have reduced accidents by half and serious-injury and fatal accidents by 60 to 90 percent. Novel roundabout designs can raise capacity substantially with no need to widen the road in its entire length, as is commonly done under traffic signal control. Like the all-way stop, the roundabout gets rid of the left-turn problem, the traffic engineer’s biggest headache.

“Most drivers do not come to a full stop but treat the all-way stop as an all-way yield. As the yield sign has a safety record as good as the stop sign but gives less delay and a 50 percent higher vehicle discharge, replacing all-way stops with all-way yields will lower road user costs substantially.”

…from Todd, K. “Traffic Control: An Exercise in Self-Defeat.”, 2004.

Regarding traffic flow efficiency The Nevada Department of Transportation offers:

More environmentally-friendly than traditional intersections due to less vehicle emissions, fuel use and noise.

“Many vehicles must wait for the light to turn green in a signalized intersection. While stopped, the vehicle’s exhaust emits more undesirable pollutants and gases into the atmosphere. Because roundabouts often eliminate such stops and improve traffic flow, they also reduce vehicle emissions and fuel consumption. In one study, replacing traffic signals and signs with roundabouts reduced carbon monoxide emissions by 32 percent, nitrous oxide emissions by 34 percent, carbon dioxide emissions by 37 percent and hydrocarbon emissions by 42 percent. Gasoline use is also reduced as traffic moves more efficiently through roundabouts, without the start and stop found at traditional intersections. Studies have shown that fuel savings can be up to 30 percent in roundabouts. At 10 intersections studied in Virginia, this savings amounted to more than 200,000 gallons of fuel per year. Without the stop and start of traditional traffic intersections, roundabouts can also reduce vehicle noise pollution.”

Safety/Other Roundabout Benefits | Nevada Department of Transportation

…and from “Impact of Modern Roundabouts on Vehicular Emissions.” Dept. of Civil Engineering, Kansas State University, 2003.

Screen Shot 2016-01-27 at 11.53.48 pm

AWSC = all-way stop [sign] control
TWSC = two-way stop [sign] control

The city of Golden, Colorado in 1999 installed a set of four roundabouts along one of its commercial corridors. Are Roundabouts Good for Business? outlines their project and includes a description of how their roundabout constructions were consistent with a subsequent and impressive increase in business square footage and annual sales tax revenues.

Vertical changes in road-beds such as raised intersections or raised individual crosswalks are also possible options to slow traffic. In my opinion the mini-roundabout is the more comprehensive solution for all the reasons presented. Its elegance eliminates stop signs entirely and fosters a fluid, continuous, mutual encounter between walkers, cyclists and motorists. That eye-to-eye contact between users is described by Hamilton-Baillie/Jones as:

“The driver becomes a citizen. Eye contact and human interaction
replaces [traffic] signs and rules.”

“Hans Monderman’s work suggests [traffic signs] also increase the
risk of accidents by absolving drivers from having to use their
intelligence and engage with their surroundings.”

…from Improving Traffic Behaviour and Safety through Urban Design, in Civil Engineering, 2005, Hamilton-Baillie/Jones

I admit I do agree with these sentiments. It is the business of our better angels, and they’ve had success with these concepts in Europe. Roundabouts do encourage these interactions between road users and that’s a good thing, but I find more comfort in the cold fact of our Hamakua Group Proposal that it’s virtually impossible to dash through a well designed Roundabout at speeds shown dangerous to pedestrians. Roundabouts are expressly designed to physically keep vehicle speeds in the range of pedestrian safety, with or without eye contact.

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