Roundabout plan leaves questions unanswered


Criticism of the plan for a roundabout at what was the “Blinker intersection” on the Edgartown-Vineyard Haven Road has not diminished since the idea surfaced five or six years ago. The current jury-rig — four stop signs — is unsatisfactory, largely because in busy seasons long backups on the state highway irritate and delay drivers. The intersection requires something better.

Whether the roundabout plan is the right answer remains doubtful for a great many Islanders, though how many cannot be accurately judged. Certainly part of the apprehension and distaste derives from several issues that need additional explanation.

For example, the key virtue of the roundabout, as described by its designers, is safety, but a review of the design and of the way the roundabout works suggests that the chief virtue is actually traffic flow. The roundabout allows throughput, and ancillary elements of its design attempt to minimize the safety hazards that result from traffic moving more briskly through the intersection.

This tension between traffic flow and safety considerations means that this $1 million construction project will be extensive as well as expensive, involving easements to enlarge the right of way and a year’s worth of construction spread out over a couple of years, because no work will be done during the summer.

The roundabout will require some driver education. Roundabouts are uncommon, and drivers may be unfamiliar with the safe techniques required to navigate such a traffic artifice. To enter roundabouts, drivers must slow down to make what is nearly a right turn, one of the designers explained last week. Today, with the four-way stop, they must stop before proceeding.

The planners say traffic volumes, despite the horrifying in-season clogs, are too modest for certain design approaches to the intersection but too high for others. That’s confusing.

A traffic signal arrangement requires construction too, one of the designers argued, “You would be talking additional turning lanes at virtually every approach,” he said.

But, discussing safety for pedestrians and bicyclists who use the bike path that runs alongside the road and through the intersection, the planners explained that their design has “splitter islands” between the traffic lanes that slow vehicles down as they enter the roundabout’s one lane. Cyclists and pedestrians may cross one lane of traffic at a time, Times writer Janet Hefler explained, using the splitter islands as a place to pause. Cyclists also have the option of riding with traffic through the roundabout.

But, doesn’t that mean that cyclists and pedestrians will need to scamper when they can across a lane of traffic that thinks it ought to keep moving, then perch on a “splitter island” until a second safe moment arrives, when the mom pushing the stroller will scamper again to ultimate safety?

Well, but there could be stop lights too, so that this imaginary mom pushes a button on the light post, stopping all traffic. But there goes the throughput.

One of the best features of the four-way stop today is that cyclists using the bike path encounter the line of traffic crossing their path when it is stopped. The cyclist can elect to cross, and the driver must choose to stay stopped while the cyclist crosses in front. It’s not confusing.

What is confusing is the argument that, although traffic flows pretty quickly through the four-way-stop intersection during eight months of the year, the traffic data, as interpreted by the designers finds little difference between off-season and in-season volumes. But, empirical evidence — that is, you driving from Vineyard Haven to Edgartown in July and you doing the same thing in January — says those data make no sense.

The roundabout plan may be the right plan — economic, safe, fluid — but the case for the wisdom of it has not been made.

It’s up to Oak Bluffs and Martha’s Vineyard Commission officials to make that case to a skeptical public. Last week’s hearing, a necessary part of the process, didn’t do the trick. A final decision requires more discussion and education.