Westbound on Evan at Santa Fe. Photo by James Taniwaki

by George Taniwaki

Take a look at the intersection above of two busy streets in Denver. The photo was taken from the left-hand turn lane of westbound W. Evan Av. turning to southbound S. Santa Fe Dr. From this angle you cannot see the on-ramp you are turning onto. It is obscured by a concrete jersey barrier.

In fact, the end of the barrier is separate from the rest of it. One gets the impression that it was originally connected to the rest of barrier but was accidentally hit, forcing it to be perpendicular to the remaining section. This creates the illusion that there is no road behind it, and you should turn left before the barrier, not after.

If you do turn left into the lane on the east side of the barrier, then you will be headed the wrong direction into oncoming traffic on Santa Fe Dr. This is really dangerous.


Synthetic aerial view of same intersection. Image from Google Maps

A better view of the intersection can be seen using the 3D tilt view feature of Google Maps. Looking at the synthetic aerial view, one can see that the intersection is directly over Santa Fe Dr. This allows large volumes of traffic to flow without taking up a lot of real estate. This configuration is called a single-point diamond interchange.

Two changes would probably make this intersection safer. First, the end of the jersey barrier should be a continuous piece of rounded concrete, not jagged, so the user can imagine there is a traffic lane behind the barrier. Second, the barrier should be set back about 3m (10’) so that a driver in the left-hand turn lane can clearly see there is a paved surface beyond the barrier before entering the intersection.

I don’t know how many accidents happen at this intersection and I don’t know how the state of  Colorado measures the social costs of traffic accidents. But if there are ten accidents (some with injuries) per year here, and the lifespan of the interchange is twenty years, then it is probably worth spending the one million dollars I estimate it would cost to make the suggested modifications to this intersection.

[Update: There was a paragraph here describing a fatal accident on Santa Fe and Dartmouth involving a driver going the wrong direction. However, that accident is unlikely to have been caused by a driver entering the highway at Santa Fe and Evans. I have deleted the paragraph.]