Anyone living in Los Angeles knows how bad traffic can get. Google Maps has a great feature that shows traffic conditions on major freeways. It's something I've been using for a while now on my mobile phone when going out around town. When you zoom in on a city in Google Maps, there's a "Traffic" button on the upper right corner that will overlay traffic conditions. It will even show you traffic conditions on a given day and time using past conditions!
Recently, I've noticed that more and more traffic conditions were becoming available for streets such as Santa Monica Blvd and Pacific Coast Highway (PCH). It turns out that Google has been able to achieve this by using the power of crowdsourcing. It does this by tracking anyone who is using Google Maps on their mobile phone with GPS enabled. As Google's blog says:
When you choose to enable Google Maps with My Location, your phone sends anonymous bits of data back to Google describing how fast you're moving. When we combine your speed with the speed of other phones on the road, across thousands of phones moving around a city at any given time, we can get a pretty good picture of live traffic conditions.
For more information, check out the post on Google's blog.