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As city populations worldwide continue to grow, more people are driving than ever before. Urban planners are looking for 1 to the problem. Some believe the answer is to make streets wider and highways bigger . However, studies show that when streets become wider, all that happens is that mor e cars come onto the roads, 2 the problem. Other studies confirm that trafficis 3 caused by too few roads or by streets that are too narrow. Researchers havefound that the main cause of many traffic jams is human decision-making. Thousandsof cars on the same road means thousands of 4 drivers making differentchoices: How fast should I go? Which street should I drive on? How far should I stay from the car in front of me? With this in mind, urban planners —— and car makers —— ar e now exploring another 5 in order to reduce traffic: driverless cars.