As a recovering roadgeek, I still get a little excited when a new highway interchange design is unveiled. This week, NPR took a look at the first “diverging diamond” in the U.S., at the interchange of MO-13 and I-44 in Springfield, Missouri. The interchange, lauded as an innovation in traffic safety, eliminates left turns across traffic for vehicles entering and leaving the highway, presumably making the interchange safer and helping traffic flow more smoothly by eliminating a cycle of the traffic light.
As for safety, Michael Trentacoste of the Federal Highway Administration says the diverging diamond interchanges are safer. “From a safety standpoint, we knew there would be less conflict points,” Trentacoste said. “You have traffic that wasn’t going to be crossing in front of oncoming traffic, because traffic is moved to the left.”
But it’s not safer for everyone. While traditional diamond interchanges have four points of conflicts for pedestrians and shoulder sidewalks, diverging diamonds have eight points of conflict. The sidewalk is no longer on the shoulder in the diverging diamond. Instead, pedestrians are forced to cross half of the arterial to reach a walkway placed in the median of the road. This, in the interest of safety, moves those pesky crosswalks out of the way of exiting drivers making a left-turn movement. On top of this, pedestrians are forced to cross unsignalized off-ramps from the highway, where drivers are not likely to have adjusted to urban speeds. Traditional diamonds, where all movements were signalized, gave a very clear indication to the driver when the pedestrian had the right-of-way. In the diverging diamond, pedestrians are left to fend for themselves on highway ramps.
Many cities have tried to find ways to reconnect neighborhoods that were split apart by urban interstate highways. NPR asks if this interchange is an idea whose “time has come.” If the time was the 1970s, when moving car traffic was the only focus and responsibility of state transportation agencies, then indeed, its time would have come (in fact, this interchange design was first used in the 1970s in France). But in an era when people are choosing not to drive and are seeking out safe means of mobility without a car, forcing pedestrians into an inhospitable environment in the middle of four lanes of fast-moving traffic is not innovative.
(photo via Google Maps)