I have a few observations about roundabouts.
I would be super bummed if the streetscape project went down the tubes because roundabouts became a linchpin issue.
Roundabouts seem to be very effective tools for some objectives and many circumstances. I think much of the friction in the streetscape debate stems from differences in objectives of the civic participants. There is also a little bit of extremism in the pro and anti roundabout rhetoric to heat things up.
Roundabouts are not universally immune to congestion jams. The traffic engineer, which much of the community stands behind, told me straight up that Leucadia should not expect the roundabouts to handle more than 10,000ADTs. He implied that we will have to do something else after that.
I wrote here about why I was so surprised that some community leaders weren't interested in analyzing the traffic engineer's work. I still don't understand how it will take longer to cross Leucadia if we are keeping the HWY 101 open at freeway speeds than if we slow traffic and incorporate traffic calming/slowing infrastructure. The explicit goal behind the project is to slow traffic down and end the Leucadia drag strip. Let me be clear; I am not disputing the engineer's result. I am only saying counter-intuitive conclusions should be explained before widely accepted and used to support a decision.
Our city seems to base everything off Austin-Foust's traffic modeling. If we want to have trustworthy traffic reports that is the first thing that has to be improved and we should not selectively reject/accept the city's traffic analysis when it is beneficial to our objectives.
Given all that, it is surprising that the city's traffic engineer said the roundabouts would eventually fail. I did not ask, he volunteered this conclusion. I suspect that he is underestimating the capacity of the roundabouts. Most of the traffic is going to be flowing north/south and there will be little conflicting traffic for most of the intersections (unless there is lots of u-turning). Uneven delays at roundabouts seem to be most likely with heavy and uniform cross traffic and that doesn't describe HWY 101 very well.
The Green Question Mark
Another argument about roundabouts is they are greener. That can not be a universal reality.
We aren't comparing stop signs and roundabouts. The comparison is signals and roundabouts.
If there is no cross traffic then a sensor controlled signal will be "greener" because cars will not be forced to slow and then accelerate back up at the intersection. Steady speeds allow for fuel to be used more efficiently. In reality, there is going to be some conflicting cross traffic at any intersection. The question is, how much cross traffic do you need before the roundabout wins the "green" contest? Here is a photo of Ponto Avenue and HWY 101 in Carlsbad.
Thousands of cars go straight through this intersection without having to slow and stop. There is very little cross traffic and very little waiting for any autos. A roundabout here would result in ALL of the thousands of cars to slow and require a few to stop. My guess is that this intersection has a smaller CO2 footprint than if there was a roundabout. Maybe not, but there is some point where the trade off does not pay back in terms of greenhouse emissions. If the decision is to be based on such things then let's do the analysis. (The analysis should not be be based on optimizing all turning motions, as is now the case in the engineer's models).
There are lots of public safety issues wrapped into the streetscape project. One that seems to be missing is emergency response times. One of the benefits of not living in rural zone is first responders can be at your doorstep in a few minutes. Fire, strokes, heart attacks, trauma and violent crimes can have very different outcomes as a consequence of delays in public safety response.
The city's fire department has said during public meetings that roundabouts can increase delays. I asked city staff about this and their response was the fire department has signed off on alternative 4a.
I am not saying that the delays should cause us to toss out roundabouts. We should make our decisions with our eyes wide open... if it matters.
One reason people like to live in low density rural zones is concrete and asphalt are not very comforting. Vegetation, vistas, open spaces and landscaping are more desirable to many.
The Streetscape Workshop 4 Series
Results of Workshop 4