Let a GPS unit guide your travel

— -- Many of us will be hitting the road for vacation this summer. Whether you're going across town or across the country, GPS units make road trips a breeze.

Global Positioning System units used to provide little more than driving directions. Today's GPS devices offer many more features. You'll find points of interest and real-time traffic information as well as MP3 players, photo viewers and audio book readers.

But before you buy a GPS unit, do some research. There are several different types of GPS units. Marine units are designed for boating. Trail GPS units are helpful to hikers. You want a street GPS unit to help you navigate streets and cities.

No matter which GPS unit you choose, it should be easy to use. But there are other factors to consider, too.

Live traffic

Some units incorporate live traffic information. You'll need to pay a monthly fee for this feature.

The traffic information helps you avoid gridlock and save travel time. This in turn helps you conserve gas. You can also find alternate routes. Some even recommend detours.

One unit to consider is the Dash Express ($400). This two-way, Internet-connected system is unlike any other. It provides real-time traffic data from other Dash users. You can also access locally relevant information from the Internet.

The Dash lets you plan routes and send them to the GPS unit. A monthly plan (about $13) is required for Internet-connected features. A one-year prepaid plan works out to about $11 a month and a two-year plan is about $10 a month.

Screen clarity

No matter what features a GPS unit offers, if you can't read the screen, it won't be helpful. Look for a bright color screen and a wide angle of view. You're a safer driver when you're not squinting at a GPS screen.

TomTom's One XL S ($350) features a large 4.3-inch touch-screen. It can be updated with real-time traffic service. You can also share your maps with others.

Text-to-speech

A crisp screen helps when you're driving, but it can't match text-to-speech. Units with text-to-speech capability read directions to you so you don't need to watch the screen. But all text-to-speech is not created equal. Look for a GPS unit that announces both distance and street names.