Comparing costs of roundabouts and traffic signals

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 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

5 thoughts on “Comparing costs of roundabouts and traffic signals

  1. The roundabout incurs additional cost for land, but a lot less equipment. An intersection with a traffic signal requires the lights, controller, sensors in the roadway, and an electrical connection. I’m actually surprised the roundabout doesn’t come out significantly cheaper, but I imagine the analysis would depend on where the intersection is.

    Personally, I’d pay more for a roundabout at that location.

  2. Yeah I agree, roundabouts are more cheaper compared to roads that requires many traffic signals. Additional acquistion of land is only necessary for a roundabout, with a regular road, you need to install warning signs, traffic lights. More power and energy is wasted.

    1. The initial cost replacing a conventional stop signed intersection with a roundabout depends a lot on the cost of acquiring the extra land required, the extra paving required, the cost of relocating infrastructure (gas, water, and sewer pipes, buried electric lines, buried telephone lines, and buried cable television lines).

      Estimates range to about a half million dollars more to build the roundabout than it would to install a traffic signal.

      Maintenance of the traffic signal would probably be higher than the cost of the maintenance for the roundabout (mowing and/or flower care).

      Pedestrian walkways might also have to be installed for a roundabout, and if it’s a busy roundabout, might make pedestrian traffic almost impossible.

      I’ve seen figures that estimate that it would cost 5 to 10 thousand dollars worth of electric to operate a traffic light. Hogwash! With LED bulbs in the traffic light, you could probably run it all year for a hundred bucks or less. Modern computers are also pretty thrifty with electric and you can probably run one all year for less than a couple hundred dollars.

      So, if you are concerned with traffic safety (not pedestrian safety), but don’t care how much it costs, you could build roundabouts. If cost is a factor (real costs, not made up ones), then a traffic signal is a cheaper solution.

  3. The first cost of any two choices is a poor way to compare. Life-cycle cost is the best (present value of future costs, a.k.a. net present value). When comparing modern roundabouts to signals for a 20-year life cycle (the standard period), modern roundabouts usually cost us much less. Costs to compare include: first cost (design/land/construction), operation and maintenance (electricity, re-striping, etc.), crash reduction (societal costs for a fatal is currently about $6M), daily delay (what’s your time worth?), daily fuel consumption, pollution (generated), area insurance rates (this costs more where it is less safe to drive – roundabouts are much safer). Each of these things, and others, can be estimated for any two choices and everyone near or using the project area will pay some portion of all of these costs.
    More info:

  4. The Federal Highway Administration uses $126,000 for an injury avoided and $6.1 million for a life saved (2009 $). The Insurance Institute for Highway Safety study of U.S. roundabouts found a 90% reduction in serious injuries at roundabouts compared to what was there before (a mix of signal and sign control). It is no mystery that for two Canadian provincial and two states departments of transportation a “roundabouts only” policy has been practice dating as far back as 2005.
    Tony Redington Blog:

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