Montgomery County’s Ride On service is adding 13 additional environmentally friendly buses, the county announced Monday.

The bus service bought 12 hybrid electric-diesel buses and one clean diesel bus. The American-made buses were purchased for $6.55 million dollars using American Reinvestment and Recovery Act funds.

These new buses will be used on route 15 (running between Langley Park and Silver Spring), route 16 (between Takoma Park and Silver Spring) and route 34 (between Friendship Heights and Wheaton). They will also be used on numerous other routes in other areas.

The buses emit less nitrogen oxides, less carbon dioxide and have better fuel economy, according to the county. The new buses mean that nearly two-thirds of Ride On’s buses will be hybrids, buses using clean diesel or buses using compressed natural gas.