Updated at 10:27 a.m. on May 13.

There was no shortage of suspects in the case of who killed the nomination yesterday of Chuck Hurley to be the new administrator of the National Highway Traffic Safety Administration. But environmental advocates - and not the carmakers or the alcohol industry - appear to be the culprit, sources tell National Journal.

Hurley, most recently the head of Mothers Against Drunk Driving, abruptly withdrew his name Tuesday, before the nomination had even been made official. While a wide array of stakeholders had expressed nervousness about aspects of Hurley's record since his appointment was announced in April, Hurley's sudden withdrawal caught insiders on all sides by surprise.

An administration official said he knew nothing beyond confirming that Hurley had withdrawn. But a source who spoke to Hurley said the former nominee cited environmentalists' concerns that he was too soft on raising Corporate Average Fuel Economy standards - the fuel efficiency requirements that NHTSA imposes on carmakers.

"He said he withdrew because he was getting opposition from the environmental community, who did not like his previous statements about the impact of raising the CAFE standards on safety," the source said.

Since his appointment, environmental advocates had expressed concern about statements made when Hurley worked for the Insurance Institute for Highway Safety. Hurley had suggested that changes in car design in response to rising CAFE standards, such as making cars smaller and lighter, were dangerous for drivers and passengers who were involved in a crash.

Environmental groups reject the notion of a zero-sum tradeoff. "I was surprised to hear he had withdrawn, but it's good to know that people are listening on fuel economy and safety," said Lena Pons, a policy analyst at Public Citizen.

Environmental critics had also cited concerns that MADD has taken money from carmakers that NHTSA regulates.

Some say the environmental pushback was somewhat ad-hoc, mainly educating key senators about Hurley's positions on CAFE standards. But the alleged ringleader - Dan Becker, a longtime Sierra Club executive who now runs a small advocacy group called the Safe Climate Campaign - declined to take credit for Hurley's withdrawal today.

"I'd rather talk about the future than guess what happened or kick a dead horse," he said, adding, "This gives the Obama administration the opportunity to choose someone who is committed to both sides of NHTSA's jurisdiction - safety and fuel economy."

While NHTSA has a number of key issues on its agenda, from child seats to bus safety, fuel efficiency and its impact on climate change is arguably the one with the highest profile.

After lengthy litigation, the Supreme Court ordered EPA to develop tailpipe standards to cut automobile emissions if they found that global warming pollution was a threat to health.  The Court said that EPA and NHTSA could work collaboratively. So President Obama, reversing the Bush administration's refusal to regulate automobile emissions, is preparing to issue CAFE and tailpipe standards for model years 2012-2016 by NHTSA's CAFE deadline of April 1, 2010.  

Becker said he expects the NHTSA and EPA to work jointly and order standards that mirror cuts mandated by the state of California -- regulations that would achieve a 30 percent emissions cut by 2016.

Other issues had been swirling around Hurley's nomination. One former transportation official said that the alcohol industry had been stung by his aggressive efforts not just to lower the allowable blood-alcohol content for drivers but to increase the court-ordered use of "interlocks" that prevent drivers from operating their car unless they pass a breathalyzer test on a machine installed in the vehicle. The Distilled Spirits Council did not immediately return a call.

Meanwhile, some sympathetic to the embattled car industry suggested concerns that Hurley would be among the agency's toughest regulators in history. But officially, the industry maintained an even keel today.

"We're committing to working closely with whomever becomes NHTSA administrator, given that position's crucial role in setting the national agenda for ever-safer and efficient cars and light trucks," said a statement by the Alliance of Automobile Manufacturers. "Effective public policy will continue to be built on industry and regulators working together to use real-world data. Consumers will always be best served when there's a shared understanding of problems and solutions."

Highway safety advocates said they were sorry to see the nomination fall by the wayside.

"I was very surprised and disappointed, and others in the safety community were caught by surprise as well," said Barbara L. Harsha, executive director of the Governors Highway Safety Association. "We were looking forward to working with Chuck on a range of behavioral highway safety issues."

The administration official said the expectation is someone new will be nominated for the post. In the meantime, Acting Deputy Administrator Ron Medford remains in charge, as he was before the withdrawal.

CORRECTION: The original version of this report misspelled Lena Pons' name.