Think taking the bus is eco-friendly? You're right, but it's certainly not because traditional diesel buses are fuel efficient. The average bus carries 40 people or more, which takes 40 CO2 spewing cars off the streets. Unfortunately the bus only gets three miles per diesel gallon, with its constant stop-and-go routine.

So what if that bus achieved ten miles per gallon? That's just what engineers in Troy, Michigan hope to accomplish with a super-lightweight hybrid bus. Fisher Coachworks is working on a bus constructed with high-strength steel expected to last longer and weigh 50% less than a typical bus.

The GTB-40 has a hybrid electric engine and uses regenerative braking to store electric energy as it slows to a stop, which should happen about every ten seconds on the average city bus route. Though the hybrid buses cost about $200,000 more than the traditional $300,000 diesel bus, the fuel savings over the life of the bus have piqued the interest of numerous cities. A hybrid bus designed to travel 500,000 miles could save a municipality more than $140,000 over its life even after the additional up front cost is added to the equation. That's assuming diesel prices stay at $2.94 / gallon, which is the lowest they've been in months.

It's no wonder that the number of buses running on alternative fuels have increased 16% in the last 12 years.

Source: Green Car Advisor, Energy Information Administration