Thanks to the modern technology that allows cars to drive using signals bouncing off satellites, we now know more than ever before just how much time we waste in traffic. A new study by the TomTom navigation service says the average driver in America's largest cities spends 20 percent more time traveling during the rush hour than off-peak -- and that aside from the neverending snarl of Los Angeles, several cities on both coasts are seeing their driving time, and heart rates, on the rise.

By measuring the travel times of thousands of drives covering millions of miles in 26 U.S. and Canadian cities, TomTom says it was able to gauge not just how much time drivers in any given city spend in rush hour, but how that flow changes between different times and different days. The results show that the differences among the worst cities aren't as great as you might think; Los Angeles drivers lose an average of 40 minutes for every hour they spend on the road at peak travel, but in Seattle it's a still-stressful 35 minutes.

The TomTom North American Congestion Index