As GPS navigation systems become more and more popular, many people are discovering the fun and utility of using real-time traffic information services. These services, which work in a growing number of metropolitan areas (check out the chart on the next page), help keep you up-to-date on traffic conditions along routes you've programmed into your navigation system. They warn you of specific traffic incidents, including accidents and construction, which usually gives you time to adjust your route and avoid getting stuck in time-killing jams.

How does it work?
Real-time traffic data is compiled by a traffic-information provider, then broadcast over a radio frequency to equipment set up to receive it. Depending on the equipment you have, you'll subscribe either to a service that's broadcast over terrestrial FM, or to one that's broadcast along with satellite radio signals. Traffic information doesn't interfere with FM or satellite radio reception, so you can continue to listen to either source while you receive traffic signals.

In terrestrial FM applications, the traffic signals are broadcast over the FM Radio Data System (RDS), a special application of the radio spectrum for sending small amounts of digital information. Most car stereos support FM RDS signals, which is how you can see radio station call letters or artist and song title information on your display when tuned to certain stations. Because Clear Channel's Traffic Message Channel (TMC)was the first widespread application of the FM RDS traffic service in the U.S., you'll often see traffic-info services which use FM RDS referred to as FM-TMC or RDS-TMC.

To use the service, simply program a destination into your navigation system. As you drive, your system will receive and deliver alerts whenever a traffic incident comes up. You'll get both an audible warning and a visual indicator on the map that's displayed on your navigation system's screen, which shows you where along your route the incident has occurred. Many systems will automatically suggest alternate routes that enable you to steer you clear of the incident ahead.

Traffic incidents include accidents, emergencies, construction, scheduled road closures, and traffic diversions for occasions such as sporting events. Some services even offer detailed information about traffic flow and the average speed along your programmed route in certain high-traffic areas of select cities.

Traffic information comes from a variety of sources, including commercial traffic data providers, departments of transportation, police and emergency services, road sensors, traffic cameras, and even aircraft reports. This information is compiled and delivered via radio frequency (FM, HD, or satellite) to your navigation system. These providers work with the two main companies behind map data for the U.S., Tele Atlas and Navteq, to deliver accurate representation of traffic data on GPS map displays.

What are the benefits?
Your primary benefit: time. More often than not, you'll get warnings of traffic incidents along your route with time enough to avoid them. And since you're using the traffic data in conjunction with a navigation system, you'll get suggestions for the most efficient alternate routes. Less time spent sitting in gridlock means more time to enjoy, well, everything.

Many portable navigation devices are compatible with live traffic information services.

You also won't have to wait for your local radio stations to deliver their scheduled traffic reports, only to find that you're heading straight for a traffic jam. The peace of mind you'll get from having a more relaxed drive also makes signing up for a traffic-information service well worth it.

Traffic-information services also let you get the most out of your navigation system. Normally, you wouldn't use a GPS unit to guide you to work, or to get you back home along roads with which you're familiar. But with a traffic-information service, you'll find that your navigation system becomes an invaluable traveling tool you'll use daily.

What do I need and how much does it cost?
Basically, all you need to enjoy real-time traffic information is a traffic-ready navigation unit and, usually, an antenna (satellite radio antennas can pick up traffic-information signals as well, if you're using a compatible satellite radio receiver).

A subscription to your service is also required. The service you use depends on the kind of equipment you have. Currently, the most popular traffic-information services are provided by:

• Clear Channel's Traffic Message Channel — also known as Total Traffic Network (FM)
• Navteq Traffic RDS (FM)
• XM Satellite Radio's NavTraffic®
• SIRIUS Satellite Radio
• MSN® Direct (wireless FM datacasting)

Satellite subscription prices range from $3.99 per month (in addition to a $12.95 per month satellite radio subscription) to $9.99 per month. Terrestrial FM services typically cost around $60 per year. TomTom has developed their own subscription-based PLUS traffic-info service, which operates through a wireless data connection with a user's compatible Bluetooth® equipped mobile phone.