It's a holiday traveler's worst nightmare.
Horns blaring, tempers flaring, you wonder what possessed you to leave home in the first place.
Well, as you climb into your car this Labor Day weekend, take heart: Technology is on your side.
From behind-the-scenes tools that transportation officials use to monitor traffic conditions to dashboard-ready, GPS-enabled mobile devices spewing real-time reports, traffic-busting technology is working to get you from point A to point B as quickly – and painlessly – as possible.
According to the American Automobile Association, about 13 percent fewer Americans will travel this weekend than last Labor Day weekend. About 39.1 million total travelers will head out of town, roughly 32.9 million by car.
"We are expecting a fairly sizeable decline in the number of Labor Day travelers from a year ago," said Geoff Sundstrom, a spokesman for the AAA national office in Heathrow, Fla.
But, he added, this weekend will still be the third busiest Labor Day holiday of the decade and it will surpass July 4 (traditionally a busier holiday) in travel.
The highest traffic day is typically Friday, particularly in the afternoon and evening when most people start skipping town, he said. Monday is also another big traffic day as people start returning home.
But, as millions of holiday-makers turn onto the highway, emergency management and transportation officials turn to the task of monitoring them.
Through sensors embedded in the pavement, installed next to highways and attached to fleets of commercial vehicles (like UPS and FedEx trucks), traffic managers keep track of accident reports, roadway closures, construction updates and anything else that could disrupt your road trip.
Michael Pack, director of the University of Maryland's Center for Advanced Transportation Technology, said a variety of cutting-edge technologies monitor and aggregate that data.
Some parts of the country use inductive loop sensors, he said, that are essentially giant metal detectors embedded in the pavement. They sense vehicles as they pass by and report how fast they are traveling and the volume of traffic.
Other areas use more advanced detectors that are installed next to the highway and emit microwaves or radar beams that bounce off passing vehicles relaying their speeds and traffic volume.
"It looks like a little shoebox mounted on a pole to the side of the road, about 15 feet off the ground," Pack said.
The newest innovation senses blue-tooth signals coming from cell phones inside moving vehicles at two locations and calculates the time it takes the cars to move between the points.
That information, along with reports sent from officials on the ground, is sent to massive regional databases that also track weather changes and other critical data.
By projecting all that information on to virtual landscapes (or dynamic real-time maps), traffic managers can see how all the factors interact, figure out how to intervene and re-direct traffic when necessary.
And, Pack emphasized, it doesn't just take an accident to cause a traffic jam.