Scientists and experts are evaluating the benefits of reducing or even eliminating left turns that have proved to cause 61% of road accidents (data from the United States). It is pointed out that the research focuses on c, the practice of keeping a vehicle on the left side of the road.
Left turns usually intercept with the course of oncoming vehicles and an error may cause severe accidents. About 40% of all accidents occur at intersections with 50% and 20% of them causing serious injuries and casualties, respectively. When no traffic signals exist, left turns require drivers to pay attention in two traffic lanes and wait for a gap to open in the opposite lane. Hence, the task is far more complex than taking a right turn. But even if traffic signals are installed, intersections become more complicated as the flow has to be halted to allow drivers to turn left, thus creating congestion.
The idea of reducing the number of left turns to promote safety is not new. UPS, the world's largest package delivery company, has changed its delivery policy to mitigate the left turns in its routes since 2004. According to the company, by following this strategy, more than 36 million liters of gas are saved, about 350,000 additional packages are delivered and the emissions of CO2 are reduced by around 20,000 tons. Recently some cities in the U.S. (e.g, San Francisco, Salt Lake City) have implemented a similar policy to reach the same goals.
Dr. Vikash Gayah, an assistant professor in the Department of Civil and Environmental Engineering at the Pennsylvania State University, is convinced that restricting left turns at intersections would increase public safety and decrease traffic. Nevertheless, he is aware that certain disadvantages will rise. The main downside is that, to avoid a left turn, people will have to drive an additional route which will consist of 3 consecutive right turns. However, research conducted by Prof. Gayah and other scientists showed that this would result in driving one additional block in grid-like networks and accounting for the amelioration in congestion, the impact in travel time will be minor when the safety will significantly increase. Prof. Gayah suggests that the matter is an optimization problem balancing between eliminating too many left turns and increasing travel time and eliminating fewer turns not taking full advantage of the concept's benefits.
Of course, left turns cannot be entirely eliminated, at least considering the structure of the current road networks. Scientists agree that the restrictions should be implemented in the busiest intersections that are usually located in cities' centers where many accidents occur. The developed models suggest that, in such intersections, the effect on traffic reduction will be significant whilst alternative routes will result in minimum travel time addition.