When driving on the wrong side of the road is the right way to speed up traffic

🌈 Abstract

The article discusses the diverging diamond interchange, an unconventional traffic intersection design that has been gaining popularity in the United States. It explores the benefits, challenges, and reactions to this innovative traffic engineering solution.

🙋 Q&A

[01] The Diverging Diamond Interchange

1. What is the key feature of the diverging diamond interchange?

• The key feature is that the right and left sides of the road cross over each other at a stop light, causing drivers to briefly drive on the left side of the road. This allows for easier and safer left turns, as there is no oncoming traffic in the way.

2. What are the benefits of the diverging diamond interchange?

• It is more efficient and safer than traditional intersections with left turn lanes:
  • It reduces the number of "conflict points" where crashes can occur, lowering the risk of side impact or T-bone crashes.
  • It allows for free left turns, eliminating the need to wait for a signal.
  • It has been shown to reduce traffic backups and delays, especially for left turns.

3. What were the initial reactions to the diverging diamond interchange?

• When first introduced, the unconventional design faced skepticism from other traffic engineers, who were hesitant about anything different.
• Some drivers also expressed concerns about the unfamiliar layout, worrying that it could confuse or endanger drivers, especially those unfamiliar with it.

[02] The History and Adoption of the Diverging Diamond Interchange

1. When and where was the first diverging diamond interchange installed?

• The first diverging diamond interchange was installed in Missouri in 2009, at a notoriously traffic-clogged intersection in Springfield.

2. How did the initial installation in Missouri go?

• The Missouri Department of Transportation was "willing to take the risk" of installing the new design. When it opened, the backups at the intersection cleared up almost immediately, and crashes were reduced by 40-50%.

3. How has the diverging diamond interchange design spread since then?

• There are now more than 200 diverging diamond interchanges across the United States, in over 30 states.
• The design has gained mainstream acceptance, though it took about 20 years for the idea to be widely adopted after it was first proposed.

[03] The Inventor of the Diverging Diamond Interchange

1. Who invented the diverging diamond interchange?

• The diverging diamond interchange was invented by traffic engineer Gilbert Chlewicki.

2. How did Chlewicki come up with the idea?

• Chlewicki had been interested in traffic engineering and road design from a young age, even drawing model roads as a child.
• He developed the idea for the diverging diamond interchange while in graduate school at the University of Maryland, and presented the first major paper on it in 2003.

3. What is Chlewicki's current role and work?

• Chlewicki is now employed by the Virginia Department of Transportation, where he continues to experiment with new "mutations" of the diverging diamond interchange, combining it with other innovative traffic designs.