Proceed with Caution

One of the reasons that a picture is worth a thousand words is because a verbal description often is confusing. Here are the words--with a picture--describing a new traffic design. (Try to read it first, and then look at the picture to see if you got close).

It’s called a diverging diamond. To enter the freeway, the cutting-edge interchange requires drivers to veer at a 45-degree angle across the center divide, switching sides with opposing traffic and briefly motoring across as if they are in England.

By being on the left side, they can then glide left onto the highway without a dangerous 90-degree turn across oncoming cars.

Some traffic planners are smitten with the concept and how, in the name of efficiency and safety, it forces opposing traffic to negotiate an X-shaped, signalized crossover before a bridge or underpass. As freeway-bound drivers drift to the left to an on-ramp, those heading through the interchange to the other side of the freeway follow the road back to the right at another crossover.

The example of the modern roundabout is instructive. While the roundabout is easy to picture, its high efficiency in moving more cars along through an intersection is difficult to apprehend unless one has experienced it a few times.

Without the "divergent diamond" schematic, your humble blogger couldn't envision even how it would work, much less whether it would an improvement. Now I'm guardedly optimistic. Traffic engineers have a good, albeit not perfect, record and have earned our trust.

As for those who are "smitten with the concept", let's pump the brakes. Don't go big until we've seen how it works on a small scale. (I'm looking at you, high-speed rail enthusiasts.)