pace car

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

• noun A usually high-performance automobile that leads a group of competing cars through the pace lap of a race but does not participate in the race.

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

• noun A car that other cars drive behind before a race starts.

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

• noun a high-performance car that leads a parade of competing cars through the pace lap and then pulls off the course