Tuesday, December 13, 2011

Roundabout benefits come full circle


Believe it or not, driving in circles can actually save fuel and reduce harmful emissions. Though it may sound counterintuitive, roundabouts actually have many environmental benefits – on top of all their safety benefits – that should put them at the top any intersection improvement list.

SR 548 Roundabout - Aerial
The safety benefits behind roundabouts are jaw dropping - reducing deaths by 90 percent, injuries by 76 percent and all crashes by 40 percent, according to the InsuranceInstitute for Highway Safety. But did you know that the efficiency and emissions statistics behind roundabouts are equally impressive?

The emissions and gas-savings stats have been less publicized, but they’re no less stunning from a sustainabletransportation standpoint. In a day and age when we’re counting every last pound of greenhouse gas released into the atmosphere, these numbers are becoming even more important.

A Kansas State University study found that replacing four-way stops with roundabouts reduced carbon monoxide emissions by 38-45 percent and carbon dioxide emissions by 55-61 percent. Nitrogen oxides dropped 44-51 percent, and hydrocarbons fell 62-68 percent.

The number and size of vehicles play a big role in emissions. Roundabouts have even greater environmental benefits at busier intersections, especially if used by lots of semis.

Aerial view of SR 539 Wiser Lake roundabout

Other studies show that when roundabouts replace intersections with or without signals, there’s a 30 percent reduction in carbon monoxide and nitrogen oxides and a 30 percent drop in fuel consumption.

The bulk of emissions aren’t necessarily from idling: We really pump the emissions into the atmosphere every time we accelerate from that stop sign or red light.

In fall 2005, the Insurance Institute for Highway Safety studied 10 intersections where traffic signals were built instead of roundabouts. The study estimated vehicle delays and fuel consumption at the signaled intersections and then compared the results to what they would have been if roundabouts had been built instead. For those 10 intersections, roundabouts would have: 

  • Reduced delays by 62-74 percent, saving 325,000 hours (37 years) of motorists’ time annually.
  • Decreased fuel consumption by about 235,000 gallons per year, for an annual savings of $587,000 (assuming an average cost of $2.50 per gallon of regular gas).
  • Caused fewer emissions and pollutants to be released into the atmosphere. 
Once a signal is installed, they’re rarely removed. They’re around for quite a few years, and their annual costs really add up over time.

The annual cost to run and maintain a signal is assumed to be about $8,000 a year. That’s $5,000 for basic electricity and routine signal maintenance and $3,000 to retime and optimize for traffic. Plus, signals get a rebuilt after 20 years – new guts and software – which costs about 30 percent of the initial cost. There are none of these costs when you build and maintain a roundabout.  

In the last four years, 14 signals have been removed and replaced with roundabouts at intersections in Washington. Today, there are 220 roundabouts total across the state, and 58 of those are on state highways.

Olympia Roundabout Looking East

Many drivers believe traffic signals are the better choice simply because that’s what they’re used to. But from safety, societal cost and environmental standpoints, the roundabout wins hands down.

If roundabouts reduce pollutants and save gas, why would anyone prefer to sit and wait at stoplight or stop sign?

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