Want to know how the economy's doing? Look at the roads. Inrix Corp compiles data from the GPS units in people's cars they say that traffic congestion has increased 10 percent in 2010 compared with 2009. But traffic is still 27 percent off its pre-recession peak in 2007.Inrix rates congestion in what it calls the "travel time tax," a measure of how much longer it would take to travel a given route in traffic than it would when there is no congestion, such as in the middle of the night. The company found that the travel time tax amounted to more than 80 hours annually of delays in peak evening travel times for some commuters. Some commuters in the 10 worst travel corridors are on track to spend an entire month per year stuck in traffic, according to the report. Most congestion is in the evening hours on roads the Federal Highway blogdogistration dubs "Urban Interstates."The study highlights some trends that commuters could take as useful tips: The worst traffic of the week is on Friday nights between 5 and 6 p.m. Evening rush hour on Thursdays and Fridays occurs about 15 minutes earlier than on other days of the week, peaking between 5:15 and 5:30 pm. Tuesdays are the busiest mornings, beating out Wednesdays in previous years. Morning congestion peaks between 7:45 and 8 am. Congestion in 2010 was higher during every hour of the week - except for a small decrease on Saturday evenings. Even weeknight traffic in the middle of the night increased as the result of more roadwork. Based on the study, Inrix expects traffic delays to be back to record levels in 2011. Lets not take for granted those of us who work and live on the Peninsula wont have to worry about spending a month out of our year in traffic.