Millions of dollars have been spent to implement it.
Traffic engineers use it to justify their employment.
Recently, this goal has increasingly been questioned, since it has led to increases in noise, pollution, accidents, global warming, and, in general, a lower quality of life. The usual justification given is that it allegedly reduces fuel consumption and emissions of air pollutants. The benefits are inferred from the smoothing of traffic. The critical questions are begged, rather than tested. There are also several other flaws in the research.