light rail

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A rail transportation system involving trolleys, streetcars, or other, usually electrified methods of conveyance, whose rails are primarily on surface streets that are shared with other forms of transportation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun US, transport A kind of rail passenger transport with a dedicated right of way, but crossing streets at grade, usually for commuters, powered by electricity, and with lower construction costs than traditional railroads.