An officer in Mountain View, California noticed a prototype vehicle travelling in a 35 mph zone at a speed of 24 mph resulting in traffic congestion. "As he approached the vehicle he realized that it was Google's self-driving car" said a post by the police department. The officer also contacted the operator to learn about the steps followed by the vehicle for choosing speed depending on roadways and make the operator vigilant about impeding traffic.
Google's self-driving car project gave response on the official Google+ page and clarified that they have put a limit to the maximum speed (i.e. 25 mph) for safety reasons. The company said most of these stops occur owing to growing curiosity of people and their desire to get a closer look. They want people to perceive the car as friendly and approachable, rather than intimidating by making them zoom scarily through neighbourhood streets. Google also said that their vehicles have driven 1.2 million miles for testing without getting a ticket. Well, that's quite an achievement and also human equivalent of 90 years of driving experience.
There is a huge market for these cars. According to a study done by IHS Automotive in January, it is expected that close to 250,000 self-driven cars would be sold each year globally by 2025.