On Tuesday, October 6, 2015 at 6:59:03 PM UTC-4, rbowman wrote:
On 10/06/2015 01:13 PM, Ian Jackson wrote:
Even though the drivers were allowed a 30 minute warm-up session before
the roundabout test, some might still not have been as comfortable with
them as they might have been. Given a bit more time to get used to them,
the roundabout throughput could well have be even higher. It stands to
reason that they will usually be more efficient then 4-way stops. Aren't
the Americans to know the phrase "We hold these truths to be self evident"?

That 30 minute warmup utterly defeats the test. What you need is a mix
of drivers, some of whom will come to a dead stop as they try to figure
out what they're supposed to do next. Roundabouts are scarce enough in
this city that a goodly percentage of the drivers have never encountered
them on their usual routes.

I respectfully disagree with your use of the "utterly", for a couple of
reasons, with #2 being the more important one.

1 - Yes, the warm up may have altered the results to some extent, but
not "utterly". Even if some of the drivers stopped, I'm confident in
saying that it wouldn't be enough to wipe out the entire 20% of
improved efficiency. There is no also guarantee that every of those
drivers have encountered - or properly deal with - 4 way stops.

2 - What exactly were they testing? They were testing the "myth" that
roundabouts are more efficient than 4-way stops. They weren't testing the
myth that some percentage of drivers don't know that to do when they
encounter a roundabout. In order to make that one-to-one comparison, you
are better off having 100% of the drivers know exactly what to do at
both types of intersections. As another example, you can't determine
whether hand brakes on a bicycle are safer than foot brakes unless the
testers know how to ride a bike. For a simple "throughput" comparison, the
fewer the variables the better.

We have both roundabouts and 4 way stops in my area. At both types of
intersections I see drivers getting it wrong (or not trusting the other
drivers to get it right.) However, having to deal with both, I'll take
roundabout every time.