The in basket: Robert Balcomb of Silverdale wasn’t satisfied
with the answer he got from the Road Warior column in December
about the comparative costs of a roundabout, such is being built
south of Silverdale, and a traffic signal there.
“Here I am again,” he wrote on May 21. The public has a right to
know what these ‘awful’ (as stated in this morning’s Sun) traffic
circles cost compared with traffic lights.
“Let the brains who decided on these monstrosities answer to
residents of the affected neighborhoods, especially those living on
the north end of Silverdale Way, who (for how many months?) must
drive miles south to Eldorado, north on Provost to get to
Silverdale. No more of their weak excuses, tell us the
dollars.”
That was missing from the December response, which instead
focused on the greater safety and lower future maintenance costs of
roundabouts.
So I asked the county for the numbers to build each.
The out basket: Doug Bear of Kitsap County Public Works says a
cost analysis comparing the Silverdale roundabout with signals
there says the roundabout would be less expensive in the first
place, $1.35 million to $1.4 million.
I don’t know how persuaded Robert and others who dislike
roundabouts will be that signals would cost $1.4 million. You can
look at that cost analysis at http://www.kitsapgov.com/pw/pdf/SWay_design_rptapp.pdf.
and judge for yourself.
Either option includes contingency allowances running into the
hundred of thousands of dollars, but those amounts are about the
same for both.
Nearly a quarter of the signals’ cost – $199,500 – would
go to constructing a soldier pile wall, nearly as much as the
$300,000 for the signal equipment itself.
Doug says “The variables in considering costs are numerous which
makes a direct comparison challenging. (Besides the initial
construction costs), ongoing maintenance costs are generally higher
for a signalized intersection than the cost of maintaining a
roundabout.
“Where long-term costs are considered, roundabouts eliminate
hardware, maintenance and electrical costs associated with traffic
signals, which can cost between $5,000 and $10,000 per year.
“Engineers also consider how the improvement affects the
capacity of the intersection, and how the improvement affects
traffic flow. Every intersection is unique, and the particular
characteristics of each project are considered as the project is
developed.
“What is clear in almost every roundabout application is that
roundabouts are safer for motorists than signalized intersections.
At a four-way intersection there are, at least, 32 possible
vehicle-to-vehicle conflicts. At a four-way roundabout there are
only eight.
“Roundabouts reduced injury crashes by 75 percent at
intersections where stop signs or signals were previously used for
traffic control, according to a study by the Insurance Institute
for Highway Safety (IIHS). Studies by the IIHS and Federal Highway
Administration have shown that roundabouts typically achieve:
· A 37 percent
reduction in overall collisions
· A 75 percent
reduction in injury collisions
· A 90 percent
reduction in fatality collisions
· A 40 percent
reduction in pedestrian collisions
The combination of lower speeds through the intersection, no
light to beat, and one-direction travel improve safety in the
intersection. In addition they also generally reduce delays and
improve traffic flow. Roundabouts promote a continuous flow of
traffic which allows the intersection to handle more traffic in the
same amount of time.”
More information can be seen at
www.kitsapgov.com/pw/pdf/silvway_Roundabout_V_Signal.pdf
