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.
Labor Day Weekend to Be Third Busiest of the Decade
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.
Traffic Managers Remotely Monitor Accidents, Road Congestion
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.
Not Just Accidents That Cause Traffic Jams
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.
"Often times, people hit a congested area and they get frustrated," he said. "But they keep driving and eventually the congestion clears up and they don't understand why there was congestion to begin with."
But, he continued, if there's an accident, or even a driver who hit the breaks unexpectedly, it can take time for the line to clear up.
Tips to Avoid and Prevent Traffic Jams
"It's like a wave propagating back down the road -- propagating backward at about 12 to 15 mph," he said. "Anyone who slams on the breaks because they saw a deer or something out of the corner of their eye, that can create a wave if there's enough traffic."
To avoid – and prevent – traffic this weekend, Pack, the AAA's Sundstrom and others offer these tips:
Before you hit the road, arm yourself with traffic information.
"When you're leaving for your destination, or you're beginning your travel home, frequently, you're going to be in a larger metropolitan area," Sundstrom said. "That is where you're most likely to encounter the most traffic."
Especially this summer, as road construction is unusually high because of new stimulus projects, he said it's important to research road work and detours and, if possible, figure out a new route.
In addition to state department of transportation sites, he suggested visiting the AAA's online interactive trip planner, TripTik. Traffic.com, which is a site managed by the private mapping and traffic company NAVTEQ, also shows construction, accidents and other traffic delays.
Monitor traffic while you're in route to your destination.
With your smart phone or cell phone, you can keep abreast of traffic conditions with a number of applications and phone services.
If you have Google Maps on your mobile device (iPhone, BlackBerry, Nokia, etc.), you can use a new, free feature that displays color-coded traffic conditions on major throughways and smaller side streets.
Whenever a user asks the phone to find his or her location in Google Maps, the phone sends anonymous data to Google describing how fast you're moving.
Google then aggregates data from thousands of phones moving around a city at the same time and calculates average speeds for different roads to provide live-traffic conditions.
TRAFFIC!, a new free iPhone application from traffic and navigation company Inrix, also provides real-time traffic data for 160,000 miles of freeways and highways in 126 cities in the United States and Canada.
Also, each state monitors and reports traffic conditions on their individual Web sites and, Pack said, many offer a 511 service that lets travelers receive the information on their telephones.
Some states even let travelers sign up for a text message service that keeps them updated on travel changes as they drive. (Visit this transportation Web site to see which states offer the 511 service.)
NAVTEQ also offers two free mobile services, a hotline at 1-866-MY-TRAFC (1-866-698-7232) and the mobile Web site mobi.traffic.com.
If you're traveling in an unfamiliar area, consider a GPS (global positioning system) device.
"It's great to have a sheet map or use Internet mapping tools, but in terms of navigating your way in unfamiliar surroundings, you just can't beat GPS," Sundstrom said.
He said the AAA has a relationship with GPS device manufacturer Magellan and that many of their products are compatible with real-time traffic services that report accidents and delays while drivers are on the road. Garmin and TomTom also offer similar services.
Even if you're not leaving town, exercise caution as you drive locally.
People in different parts of the country are used to different driving patterns, Pack said. And out-of-towners can throw off the balance on the road, which can lead to accidents.
"The folks that are local need to adjust their driving patterns and keep their eyes open for slower drivers," he said.
They should be extra safe all the time, he said, but especially so during holidays when more visitors are around.