traffic island

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

• noun A raised area over which cars may not pass, placed at a junction of thoroughfares or between opposing traffic lanes.

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

• noun A stretch of raised concrete in the middle of a roads used to prevent drivers from driving into oncoming traffic or private roads.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a curbed area in a roadway from which traffic is excluded; provides safe area for pedestrians