Brighton's diverging diamond shines

A little more than a year after New York's first criss-cross intersection opened in Brighton, the accident rate has been cut in half and the public reviews are generally good.

The interchange of South Winton Road and Interstate 590, long the scene of rush-hour backups and accidents, was rebuilt last year in what's known as a diverging diamond configuration.

Traffic on South Winton now crosses over and drives on the left side of the road near the ramps leading to and from I-590, making it easier for vehicles to flow onto the ramps without stopping. Those ramps were a big choke point before, New York state transportation officials say.

"It looks like the project is doing what it was supposed to do," said Lori Maher, the local spokeswoman for the state Department of Transportation who found herself explaining the unusual traffic pattern to the public and journalists over and over again during the four years between the time the concept was broached and project completion in September 2012.

Fears of mass confusion and head-on crashes were not realized. In the first six months of operation, Brighton police logged 21 accidents at or near the intersection — half the number that occurred in the same period in each of the two previous years.

And none of them was head-on.

"That's a significant decrease in the motor-vehicle accidents in that area," said Police Chief Mark Henderson, who admits he was a skeptic when he first heard of plans for the redesign. "My observation has been we don't have the backup we had before with cars wanting to turn left. It seems to flow a little bit better."

Motorists themselves also judged the rebuilt interchange more efficient and less threatening, according to an analysis of before-and-after surveys filled out by drivers who travel that route.

"The results indicate that, overall, the DCD (diverging diamond) interchange was rated much safer than the previous … interchange," the analysis states. "The afternoon rush hour was perceived to show the largest safety improvement."

The afternoon rush hour featured the worst back-ups, which are now eased because northbound and southbound vehicles can enter I-590 ramps at the same time without having to wait for traffic signals.

The analysis was written by researchers at North Carolina State University's Institute for Transportation Research and Education, which was engaged by federal highway officials to study driver perceptions of a number of new diverging-diamond interchanges.

Researchers provided a draft of the analysis to the Democrat and Chronicle. The survey forms were made available to motorists who had signed up for DOT project updates and on the agency website. The interchange was rated by 98 people before the reconfiguration and 133 people afterward.

There were some negative written statements added by people taking the survey, just as there have been a few sour notes sounded in comments submitted to the Democrat and Chronicle over the past year.

But the post-construction responses to the survey were, in the main, exceedingly positive. Drivers indicated they felt much safer making a left turn onto an I-590 ramp and thought the intersection seemed less congested than it had been. They even found the new criss-cross setup no more confusing than the standard interchange it replaced.

Pedestrians and bicyclists, who had worried about negotiating the intersection, also saw improvements. The analysis noted, though, some "points of concern" remain in those areas.

The diverging diamond concept was pioneered in France. The first one in the United States went into service in Springfield, Mo., in 2009, with the Brighton interchange among the first dozen or so to be finished in this country.

The $5.7 million project and the Rochester-based firm that provided engineering and construction support, Erdman Anthony Engineering Services, recently were honored in the transportation category of the New York Engineering Excellence Awards competition and are eligible for New York project of the year.

While New York state has no more diverging diamonds on the books at present, they're being built with increasing frequency in other states. They're popular as congestion-relievers because they usually require little additional land, can be built quickly and are relatively inexpensive — especially if, as was the case on South Winton, the existing bridge carrying the expressway over the surface road doesn't have to be replaced.

"It's a great value," Maher said.

SORR@DemocratandChronicle.com

Twitter.com/SOrr1