Google's done it again: Having divined the killer app for Web navigation, the search engine is now empowering commuters to easily navigate the world of public transportation. If all goes well, the new Google Transit Trip Planner will help expand the use of this eco-friendly form of transit and reduce America's onerous oil demands.

Now in a Beta rollout phase, the experimental tool is only available for Portland, Oregon's TriMet system, but judging from the positive response so far, it should be coming soon to a city near you.

Say you want to get from the suburbs to downtown. Just plug in your point of departure and destination, and the transit tool will reveal the quickest route to the nearest bus or train station, what lines to take, and the schedule and cost of your trip. It even compares the price of public transport to the cost of traveling by car – yet more incentive to opt for planet-friendly transit.

According to Jeremy Faludi, a contributor to the excellent blog, WorldChanging.com, “One of the biggest obstacles to people using public transportation is learning how the system works—where to go, when to go, etc…Having transit trip-planning data readable and presentable by a clean, easy-to-understand, universal tool will make a big difference.”

Image credit: Google Transit Trip Planner