By Susan Heavey

WASHINGTON (Reuters) - New Jersey Governor Chris Christie fell to ninth place from his top spot among favored U.S. politicians after a scandal over traffic lane closures on the George Washington Bridge, according to a Quinnipiac University ranking released on Thursday.

The poll measuring Americans' sentiment toward political leaders was taken last week as the well-known Republican, who is often mentioned as a possible 2016 U.S. presidential contender, released an internal investigation two months after the lane shutdown popularly referred to as "Bridgegate" came to light.

Christie lost the No. 1 spot to populist Senator Elizabeth Warren, a Democrat from Massachusetts, in Quinnipiac's "National Thermometer" poll.

Former Secretary of State Hillary Clinton, also a Democrat, came in second.

Researchers asked nearly 1,600 registered voters to rate politicians on a scale of 0 to 100, with higher numbers indicating "warmer or more favorable" feelings.

People rated Christie "a chilly" 45 degrees. That was down from nearly 56 degrees in January, before the bridge scandal erupted in the national media and raised questions about the governor's ability to compete successfully as Republicans seek a candidate for the 2016 presidential election.

The poll, taken from March 26 to March 31, has a margin of error of 2.5 percentage points.

On March 27, a law firm hired by Christie exonerated the governor and cleared his current staff, but many critics dismissed the findings. A day later, Christie announced that the chairman of the Port Authority of New York and New Jersey resigned.

Americans have warmed to other Republicans, researchers found, although many respondents said they still did not know enough about them. U.S. Representative Paul Ryan of Wisconsin,

Louisiana Governor Bobby Jindal and Wisconsin Governor Scott Walker all earned about 47 degrees on the index.

Warren came in first with nearly 49 degrees, but nearly half of those polled said they did not know enough about her.

In contrast, just 1 percent said they did not know Clinton, a former U.S. senator who has been a national figure since she became first lady in 1993. She came in with nearly 48 degrees.

(Reporting by Susan Heavey; Editing by Lisa Von Ahn)