tdol said:
If you're interested in the British term, we call it the 'central reservation'. If not, I'm sure an American speaker will be along soon.;-)
I've always called it just a median, but I got curious and looked it up. See what I've come up with. (from the American Heritage Dictionary)
median strip n. The dividing area, either paved or landscaped, between opposing lanes of traffic on some highways. Also called Regional: boulevard. Regional: boulevard strip. Regional: mall1. Regional: medial strip, median. Regional: meridian. Regional: neutral ground. See Regional Note at neutral ground.
REGIONAL NOTE: The strip of grass dividing the opposing lanes of an avenue or a highway is known by a variety of terms in the United States. The most common term is median strip or median. In upstate New York it is called a mall, and in Pennsylvania, a medial strip. In the Upper Midwest the strip is known as a meridian, a boulevard, or a boulevard strip. In Louisiana and southern Mississippi the term used is neutral ground—“as if the highway were a battle zone,” observes Craig M. Carver in American Regional Dialects.