I disagree with Todd Litman's item 3. Properly designed true modern roundabouts
are bike&ped friendly, and universally safer than traffic signals. It is the VT
Bike/Ped Coalition's policy to support installation of true modern roundabouts.
I do find that traffic engineers, and some transportation planners (Tony
Redington), are too quick to accept multi-lane roundabouts in their zeal to
demonstrate how much more traffic can be processed through roundabouts than
signalized intersections. Multi-lane roundabouts lose some of the elegance and
human-scale of single laners. Let the cars queue!
I reviewed the source for the "traffic circles are terrors" quote
found the site to have an uneven sophistication about modern traffic concepts.
The PTI site does not distinguish between high-speed, merging traffic circles,
Seattle-style "traffic circles", Australian versus British roundabouts, normal or
mini-roundabouts. Other pages at the site confuse bumps and humps while being
ignorant of cushions, H-shaped humps and other vertical variants.
I think the quote cannot be fairly considered to refer to true modern
roundabouts. Even if it is aimed at roundabouts, it should be grouped with lame
protestations like "Americans are too dumb to figure out how to drive through a
roundabout," or "roundabouts don't work in the winter."
Despite my warning to consider induced or "generated" traffic from roundabouts, I
believe Tony should receive high commendations for pushing roundabouts. A
carefully crafted, single-lane, modern roundabout is the closest approximation of
a silver bullet for reducing pollution, reducing wear & tear, reducing crash
casualty, and improving walkability, bikability and livability.
Todd Litman wrote:
> I agree that modern roundabouts (which have specific design characteristics
> discussed at http://www.roundabouts.com) have a number of advantages over
> signal controlled intersections. However, I can't help but be somewhat
> skeptical of the estimated fuel savings/emission reductions for the
> following reasons.
> 1. A 5% reduction in total state vehicle fuel consumption due to 100
> roundabouts seems too high. Motorists only encounter a few intersections
> suitable for conversion to roundabouts on a typical trip, and the positive
> effects last only a few hundred meters or seconds. I simply can't see how a
> change in traffic patterns that affects perhaps 1% of total vehicle travel
> can reduce fuel consumption by 5%. I would need to see some independent
> review of this analysis before I could accept these estimates.
> 2. As described by Peter Duval, the estimates do not take into account the
> additional travel that is "generated" by reduced delay. At least a portion
> of the projected fuel savings and emission reductions are likely to be lost
> to this takeback effect. For discussion see the paper "Generated Traffic;
> Implications for Transport Planning" available at our website.
> 3. Although I agree with Mr. Redington's suggestion (in other papers he's
> written) that making roads more compatable to cycling and walking is
> critical to creating more "sustainable" transportation systems, roundabouts
> themselves have mixed impacts on non-motorized travel. For example, one
> commentor states, "Traffic circles are terrors for bicyclists. As the
> cyclists hug the right side of the road in the circle, cars suddenly turn
> into their lanes to exit from the circle." ("Bicyclist: Caught in the
> Middle," PTI,
> There are a number of ways to improve walking and cycling conditions and
> encourage shifts from driving to non-motorized travel that have much
> greater impacts.
> It is wise to be skeptical of single solutions to our transportation
> problems, whether it be roundabouts, telecommuting, a new transit line, or
> hypercars. I would rather see Transportation Demand Management emphasized
> as the way to encourage more efficient travel, traffic calming recoognized
> as an important TDM strategy, and consider roundabouts to be an important
> traffic calming device. This takes a more systematic approach which greatly
> broadens the range of solutions to be considered. It also recongizes that
> engineering strategies which improve traffic flow have a role, but that
> such measures must be balanced with disincentives to driving (for example,
> cashing out free parking, distance-based insurance, reduced traffic speeds
> between intersections, etc.) if the anticipated benefits are to be achieved.
> For more information see the reports "Comparing Emission Reduction
> Strategies," "Potential TDM Strategies" and "Win-Win Transportation
> Management Strategies" posted at our website.
> Todd Litman, Director
> Victoria Transport Policy Institute
> "Efficiency - Equity - Clarity"
> 1250 Rudlin Street
> Victoria, BC, V8V 3R7, Canada
> Phone & Fax: 250-360-1560
> E-mail: [log in to unmask]
> Website: http://www.islandnet.com/~litman
> At 08:15 PM 6/8/99 EDT, Tony Redington wrote:
> >SOME REFLECTIONS ON THE CLEARWATER, FLORIDA ROUNDABOUT PROPOSAL THAT
> >ESTIMATES ANNUAL MOTOR FUEL USE REDUCTION OF ABOUT 200,000 GALLONS BELOW A
> >TYPICAL SIGNALIZED INTERSECTION
> > The Breakthrough Proposal
> > Ken Sides is a Clearwater, Florida, City traffic calming engineer,
> >who developed a "Gateway Roundabout" proposal (May 11, 1999) that involves
> >replacing three signalized intersections with a single large roundabout with
> >annual fuel savings of 579,255 gallons--almost 200,000 gallons reduction per
> >replaced traffic signal--and using the federal method, reduces pollution
> >emissions by 68%.
> > Sides worked with Florida state highway staff in preparing this
> >Congestion Mitigation and Air Quality (CMAQ) proposal and with US roundabout
> >expert Michael J. Wallwork, P.E. of Jacksonville, who employed the popular
> >roundabout software SIDRA for the fuel savings, an 18-year-old software
> >routinely used by Florida officials for valuation of CMAQ proposals.
> > Note a fourth stop controlled intersection is also absorbed by the
> >roundabout but either has little impact on the overall figures or is left
> >of the Sides proposal analysis. involved
> > The Numbers
> > Federal air quality officials utilize a far less sophisticated
> >intersection evaluation software than SIDRA for identifying fuel and
> >emissions, the Environmental Protection Administration's (EPA) Mobile 5E
> >model. It credits only the stopped delay, that is the comparative time a
> >vehicle sits at an intersection idling, for emission reduction. Even using
> >the EPA or federal method, the fuel reduction per roundabout over the
> >signalized intersection was 89,133 annually. Interestingly, the stopped
> >delay also translates to fuel use as Vermont air quality officials
> estimate a
> >composite vehicle motor fuel use at idle is about one gallon per hour.
> >Therefore all fuel savings under the federal stop delay method also equate
> >hours of delay for motor vehicle operators and their passengers.
> > SIDRA measures the fuel used in slowing down or stopping (by lane)
> >from cruising speed before the intersection and the full period of
> >acceleration to cruising speed after the intersection.
> > While the proposal does not provide the entering vehicles per
> >intersection, each peak hour was multiplied by 10 to give a reasonable
> >dimension: the traffic signal intersections daily entering traffic numbers
> >were about 18,500, 26,390, and 19,450. The roundabout to replace those
> >intersections has an entering volume of about 40,850.
> >The reduction in fuel usage annual provided the roundabout is:
> > Before/After Fuel Use Reduction (gallons)
> > EPA Mobile 5E
> > Three Signals to Roundabout 267,399 579,255
> > Per Signal to Roundabout 89,133
> > Note the average delays for the three traffic signals at peak hour
> >delay compared to the roundabout's 16.4 seconds is not particularly
> > The traffic signal delays are 27.9 seconds, 21.2 seconds, and 13.3
> >Of course off-peak hours result in very little change in traffic signal
> >delay, but for a roundabout off-peak delay drops to 3-4 seconds average.
> > For a rural state like Vermont, a hundred roundabouts replacing
> >traffic signals at moderately busy intersections would result in savings
> >about 20 million gallons of motor fuel, with the latest federally reported
> >annual use of 400.7 million, or a reduction of 5%. (For comparison, in
> >Vermont a reduction of the rural interstate speed limit from 65 mph to 55
> >mph, a real decrease of about 3 mph, would reduce fuel consumption by about
> > Sample Vermont Intersections
> > Here are some typical Vermont intersections and the total entering
> >traffic numbers from the Vermont Agency of Transportation's "1996 (Route
> >AADT's State Highways," 1997. First, the US 5/VT 9/Brattleboro State
> >intersection is being changed from a traffic signal to a roundabout with
> >construction expected to be complete by October 1999. Second, while a stop
> >control intersection versus a roundabout may not result in a large saving
> >based on stop delay alone, it is still significant. Based on a 2 second
> >delay differential which is the federal method for the Keck Circle
> >in Montpelier, Vermont--the roundabout delay less than the stop control
> >delay--annual savings about to 2,200 gallons of motor fuel.
> > Here is a sample of Vermont intersections with entering daily traffic
> > Traffic Signal Entering Traffic (daily)
> >Rutland US7 (Main St.)/US 4 (Woostock Ave.) 26,000
> >Montpelier US 2/US 302 (Walker Motors) 19,300
> >Williston US 2/VT 2A (Taft Corner) 24,700
> >Bennington US 7 (North/South St.)/VT 9 (Main St.) 25,950
> >Brattleboro US 5/VT 9/Brattleboro St. Hwy. (Keene Turn) 27,500
> > Other Roundabout Virtues
> > The Ken Sides findings have enormous import for fuel conservation and
> >air emissions policies. But this should not obscure the other--and perhaps
> >even more meritorious, if that is possible--benefits conferred on society by
> >the roundabout. These include: (1) reduction in pedestrian and car occupant
> >collisions by half and injuries by 70% (plus reduced injury severity); (2)
> >lower capital and operating costs or roundabouts over traffic signals; (3)
> >improving transportation access and facilitating bicycle/pedestrian modes,
> >thereby reducing sprawl and increasing existing/planned development
> >densities; and (4) aesthetic benefits.
> > Tony Redington 802-828-5755
Peter K. Duval +1 802 899 1132
98 Sleepy Hollow Road fax: 899 2430
Essex Junction, VT 05452-2798 [log in to unmask]