EVERY ONCE in a while in the blizzard of traffic studies churned out by "blue-ribbon" commissions, academics with grants and various connoisseurs of the obvious, some marvelously basic recommendations emerge. Such is the case with a "new" national traffic study just released by the Insurance Institute for Highway Safety. It points up a number of relatively simple, inexpensive ways to dramatically reduce traffic accidents in urban areas. As reported Sunday by The Post's C. Woodrow Irvin, the safety organization worked with Virginia Department of Transportation engineers to test certain changes in left-turn designs and other road controls that, over a 41/2-year period, sharply decreased the number of crashes in the Tysons Corner area.

Police reports for that area had revealed a pattern in the types of crashes there, especially left-turning vehicles being hit by oncoming traffic or smacked from behind. The study concluded -- imagine this -- that adding a green-arrow signal to an intersection and converting a left lane into what VDOT calls a "protected" lane (left only on green arrow) worked wonders.

At Leesburg Pike and the entrance to Tysons Corner Center, for example, the arrow-lane conversion dropped the number of collisions with oncoming vehicles in two years from nearly nine to none. At Leesburg Pike and Lewinsville Road, where such crashes were frequent, the number of collisions sank from about five a year to none in 21/2 years. Clearly, giving left-turners a protected break to do their thing is safer than leaving them to chance a duel with oncoming traffic. Nothing revolutionary, just common sense for a busy urban intersection. The study cited still other what-took-so-long changes that have improved safety, including extending merge lanes and moving certain bus stops a few hundred feet.

The institute study notes that while most fatal car crashes nationally occur on rural roads, about 8,000 deaths and more than a million injuries happen on streets in urban regions. The findings and proposals may not rock the traffic world, but if the study prompts other state and local officials to put a few more green arrows in their quivers and look for additional simple fixes for deadly problems, it will be a lifesaver.