Most navigation apps can get you from A to B while avoiding traffic snarls, but they rarely give you a feel for how risky the drive might be. Is that intersection a cake walk, or a death trap? Waze thinks it can help. It's now alerting drivers in five big US cities (Boston, Los Angeles, New York, San Francisco and Washington) when they approach intersections with historically high crash and injury rates -- get close to one of these danger zones and you'll get a reminder to drive carefully. This won't do anything to stop other drivers from ruining your day, but it should prepare you for the dangers ahead.