Portable GPS navigation systems: a boon to road worriers.(up front: News/Trends/Advice)(Buyers guide)

A portable navigation system could be just the thing if you often travel to new places, have map-reading issues, or simply hate asking for directions. Although not as easy to use as the best built-in systems in new cars, portables can be moved from car to car (they weigh between about 5 ounces and 21/2 pounds), and most will easily fit in your luggage. Most cost far less than built-ins (about $350 to $1,200 vs. up to $2,000). And there's no monthly fee involved, except for the real-time traffic reports available with some models.

Like built-ins, portables have a map-display screen driven by an internal database. An integral antenna receives Global Positioning System (GPS) information to determine your whereabouts. You pick a destination by entering an address or selecting from "Points of Interest" such as restaurants, gas stations, and ATMs, and the device speaks and shows you where to turn. You can program the system to avoid toll roads or freeways, or pick the shortest or fastest route.

Portables generally attach to the windshield with an included suction cup. Unlike built-in navigation systems, they can come loose in an accident and are at risk of theft, so you should remove them when they're not being used.

We tested 15 portable nav systems, focusing on ease of use and the information provided to the driver.

How to choose. Look for these attributes:

* A touch screen, found on most systems. Your fingertip is easier to use than a stylus, needed on the Navmans, Mio, and Pharos.

* A preloaded, detailed electronic map of the whole U.S. (With the Navman iCN520 and Pharos, you need to load map data segments from a PC into the system's memory, a tedious job.)