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   San Francisco

September 27, 2002 

Get rid of diamond lanes

For more extensive discussion see How to Increase Crash Risk, Fuel Consumption, and Exhaust Emissions

BY LEONARD EVANS
Special to The Examiner

    DIAMOND LANES make my frequent trips to California even more enjoyable. Accompanied by my wife, I drive a rented car effortlessly around your beautiful state. My progress is not impeded by the majority of vehicles. They are prohibited from entering my lane because they contain only one person.

    However, my 30-plus years experience as a traffic researcher specializing in safety convinces me that diamond lanes increase crash risk, increase fuel use and increase exhaust emissions.

    They increase crash risk in a number of ways: Minimizing relative speeds between vehicles is a safety goal. Yet the very purpose of diamond lanes is to artificially generate a speed difference between vehicles in adjacent lanes. Diamond lanes motivate eligible drivers traveling even short distances to weave through three lanes of traffic. Every lane change increases crash risk. Some drivers in diamond lanes end up traveling faster than they consider appropriate for themselves or their vehicles. I could not fail to notice a higher density of skid marks in diamond lanes compared to in other lanes.

    When traffic is congested, the slower it moves, the more fuel it consumes. Fuel use increases rapidly with further reductions in trip speed. A situation in which some vehicles travel in very congested traffic while others travel in lightly congested traffic uses more fuel than one in which all vehicles travel in moderately congested traffic.

    By causing almost all traffic to move slower during peak periods than it would if all lanes were available, the overwhelming majority of vehicles consume more fuel. The vehicles in the diamond lanes are so few that even if they were magically using no fuel at all, the aggregate effect would still be an increase in overall fuel use.

    Exhaust emissions generally increase even more steeply than fuel use in response to vehicles accelerating after being slowed down by congestion.

    One cannot fail to be astonished that a democracy can support a policy that penalizes the vast majority in order to benefit a small minority. The minority enjoy lower fuel costs and shorter trip times. The majority pay increased fuel costs and suffer increased delay. However, all members of the majority and the minority are at increased risk of injury and death, and everybody breathes dirtier air.

        Leonard Evans is president of Science Serving Society in Bloomfield Hills, Mich. He is author of the classic book "Traffic Safety and the Driver", a member of the National Academy of Engineering and author of over 100 technical papers on traffic safety.