TriMet announced Friday that it will test its first all-electric bus on selected routes over the next two weeks.

If you're lucky and the zero-emissions Build Your Dreams Motors bus pulls up to your stop, you get a free ride.

Here are eight things to know about the greenhouse-gas-fighting machine and TriMet's upcoming experiment:

1. Why will rides be free on the e-bus? The bus isn't equipped with a fare box or ticket printer. Of course, any transfers to other TriMet buses or trains will require a fare.

2. This is just a test drive. TriMet hasn't purchased an electric bus yet. But the agency recently submitted a grant proposal to the Federal Transit Administration for $5.6 million, with a $5.3 million TriMet match, to purchase a total of nine electric buses and charging stations next year. The match would come from TriMet's general fund.

3. The potential long-term savings to the agency are encouraging. "Initial testing of BYD's buses has suggested substantial operating cost savings not only compared to 40-foot diesel, CNG, or Hybrid Electric buses, but also competing manufacturers' battery electric buses," said TriMet's Angela Murphy. Build Your Dreams (BYD) promises that combined energy and maintenance savings would offset the initial purchase price.

The nine electric buses would reduce TriMet's diesel consumption by about 89,000 gallons annually. At an average cost of $3.15 per gallon, when purchased in bulk, TriMet would save more than $280,000 in diesel fuel costs annually. Of course, the savings would be offset by the cost of electricity (ranging from $90,000 to $120,000 annually) used to recharge the buses.

4. BYD Electric buses run entirely off battery power lasting up to 24 hours on a single charge, with single off-peak charging time of two to four hours. The nine buses would reduce emissions of nitric oxide and nitrogen dioxide that contribute to the creation of ozone by an estimated 330 kilograms per year, and carbon dioxide greenhouse gas by an estimated 896 metric tons per year, TriMet said.

5. The buses run entirely off of an electric powertrain, with no transmission or internal-combustion engine.

That means there's no engine noise to warn pedestrians that a huge people mover is coming their way. So, TriMet is exploring ways add artificial noise if they go through with the e-bus purchases.

6. Murphy said the BYD battery's chemistry is environmentally friendly, "making it disposable and pollution-free with zero emissions."

7. The bus will pick up riders on various unannounced routes, adding trips between regular week day service, beginning Monday and running through the first week of July. The goal is to simulate actual operating conditions – including stopping, starting, light and heavy loads.

8. This is just the very beginning of mass transit agencies using electric buses. Check out this bus that can charge itself at every stop in as little as 15 seconds.

-- Joseph Rose