Consider the following…
You’re driving in an urban setting from Point A to Point B. Assume reaching your destination requires turning both left and right at intersections, but you’re only permitted to make right turns. You might think that restriction wastes fuel – you would be wrong. But we’ll get back to that in a moment.
To minimize the risk of collisions in urban intersections, as standard operating procedure some shipping companies employ routes favoring right turns. Despite the additional time required, these companies have determined that it is ultimately less expensive to route their delivery trucks in this manner.
Mythbusters tested this scenario in San Francisco and found that despite extending the travel time by 17%, the right-turn-only-route consumed less fuel compared to the route that incorporated both right and left turns.
Your typical driver is probably not going to consider somewhat better fuel economy as more valuable than the time lost driving (toward their destination) in circles. Although no one would argue that safer roads are needed, adoption of the right-turn-only constraint seems a very unlikely future. There is however, an alternative:
A superstreet is a type of road intersection that is a variation of the Michigan left. In this configuration, traffic on the minor road is not permitted to proceed straight across the major road or highway; traffic wishing to turn left or go straight must turn right onto the major road, make a U-turn through the median a short distance away from the intersection and then either go straight or make a right turn when it intersects the other half of the minor street… This description assumes driving on the right.
North Carolina State University reported their findings on a recent superstreet study:
- 20% overall reduction in travel time – unfortunately, the report did not mention fuel economy for comparison
- 46% fewer reported automobile collisions (63% fewer resulting in personal injury)
The usability of intersections could be redesigned to potentially improve efficiency and safety throughout the nation, but at what cost? Is the superstreet redesign the correct application for all urban intersections? Or perhaps we should consider employing a right-turn-only constraint as a viable low-cost alternative to re-architect our infrastructure. The learning curve would be lower, and the changes would be far less disruptive. Without additional data and user feedback I’d just be making right turns to wrong conclusions.