Why do you need to conjecture when the data is easily available? The list of every traffic light in Seattle is at https://data.seattle.gov/Transportation/Traffic-Signals/dr6d... . You can unzip it and open WGS84/TrafficSignals.dbf in LibreOffice as a spreadsheet. There are 1077 traffic lights in the city, according to those records.

Of them, 85 are "FULL", 271 are "PRE", and the remaining 721 are "SEMI". Based on http://ops.fhwa.dot.gov/publications/fhwahop08024/chapter5.h... these appear to mean respectively "Fully-Actuated", "Pre-timed", and "Semi-Actuated", so 271 or 25% of your cities traffic lights are on a timer and don't have vehicle detectors.

Your original example was of an intersection with "cameras mounted pointing all 4 ways", making it fully-actuated. There are only 85 of those signals in Seattle, or 8% of the signals.

To be fair to you, you said "on an arterial". However, your definition of "arterial" appears to be different than Seattle's, which subcategorizes them as 'Principal Arterials', 'Minor Arterials', 'Collector Arterials'. See http://www.seattle.gov/transportation/streetclassmaps.htm . More specifically, the map at http://www.seattle.gov/transportation/streetclassmaps/planwe... shows more than 85 intersections of an arterial with an arterial, so the pidgeonhole principal say it shouldn't be hard to find an intersection that isn't fully actuated.

To be fair to me, this is completely besides the point. There are many solutions to your original problem of being stuck at a light. One is to add another layer of technology (smarter signals). Another is to switch to a different type of technology (roundabouts). All you've been doing is cherry picking your observations to justify your initial beliefs. I further believe is because you, like many other programmers, are philosophically inclined towards complex, centralized control systems, because that's what we understand and work with all day.

But the observational evidence is that roundabouts are better than signals for many situations. Please stop ignoring the evidence because your mind is set on the first solution you came up with while your were stuck at that traffic light!

For examples drawn from Seattle, from these meeting notes in 2006 at http://www.seattle.gov/transportation/docs/setscctnov06%20mt... :

> The City Council did not vote to eliminate the roundabout proposed at 51st Ave S, Renton Ave S and S Roxbury ST from the Transportation Capital Improvement Program (CIP). SDOT has secured a grant for $1.7 million to design and build the roundabouts; unfortunately, based upon preliminary design and cost estimate, additional funding is necessary. If built, it would be the first roundabout in Seattle. The project was identified in the Rainier Beach Neighborhood Plan as the most problematic intersection in SE for all modes. The roundabout could be a very cost effective solution as unlike a traffic signal, it will have minimal on-going operating and maintenance costs. Environmentally, it's better than a traffic signal because vehicles would not be idling at the light. It is also far friendlier to pedestrians, which would have the right away and not have to find the pedestrian push buttons. CCT members reiterated that the area is routinely congested and difficult to negotiate.

and from http://www.seattle.gov/transportation/docs/nctipf_chapter%20...

> Modern roundabouts can provide safe and cost-effective traffic control at some intersections. A roundabout separates through and turning traffic into designated lanes with “splitter islands” to minimize traffic weaving. Well-designed and appropriately placed roundabouts also provide safer pe
destrian crossings and can accommodate large turning radii required by trucks and emergency vehicles. Today’s roundabouts do not function like the large, high-speed traffic circles found in
Washington, D.C., (Dupont Circle) and Paris (Arc de Triomphe). These large traffic circles have high crash rates, largely due to high volumes, high speeds, and a considerable amount of weaving between entries and exits. Roundabouts are not the small circles used primarily for neighborhood speed control. Studies of modern roundabouts show a reduction in serious crashes, as well as reduced delay and queue length compared to other forms of traffic control, such as four-way stops and traffic signals. However, engineering analysis will not always support a roundabout over a traffic signal or other traffic control measure. Consideration must be given to traffic volumes, capacity requirements, available right of way, and cost.

There's a newspaper article from 2002 which concerns a successful roundabout in Snohomish County, at http://community.seattletimes.nwsource.com/archive/?date=200... . A round-about replaced a stop sign, and reduced the number of accidents. While it cost $310,000 and "traffic signals at that location would cost only $200,000, the roundabout requires no mechanical maintenance or electricity, making long-term costs comparable, he said. Meanwhile, traffic flows much more smoothly without a signal or stop signs."

The article also says "DOT built its first state-highway roundabout in 1998 in Port Orchard, where a triangular intersection on Highway 160 had produced 39 crashes in three years. In the first 18 months after the roundabout opened, only two accidents occurred."

Continuing from the article, "National studies show that communities usually oppose the idea at first, DOT engineer Brian Walsh said. "Our experiences here in Washington have mirrored that; we have had a lot of people not very happy about the idea of roundabouts, but after they are constructed, those fears mostly go away."

which is why when SDOT brings it up over the years, there's pushback, like:

> The roundabout concept has generally received positive or neutral comments, but there is skepticism about the feasibility of building it and also some concern about the amount of land that would be required to build it, as well as the adjustment needed for motorists to learn how to drive this type of facility. - http://www.seattle.gov/dpd/cs/groups/pan/@pan/documents/web_...

I can accept an argument that people in Seattle won't use roundabouts because no one there has the political will to push for what is, really, a safer system. But your arguments so far haven't been anything better than "trust me, I know what I'm talking about". ... Which is exactly how the current system of "smart" (ie, actuated) but dangerous traffic signals were sold to us 20 years ago.