Michael D. Shear

Ray LaHood, the former Republican congressman from Illinois who has run the nation’s Transportation Department under President Barack Obama, will not serve a second term, he told department employees in a letter Tuesday.

“I’ve told President Obama, and I’ve told many of you, that this is the best job I’ve ever had,’’ LaHood wrote.

He cited the department’s efforts to curb distracted driving and to increase the efficiency of automobiles by raising emissions standards.

As transportation secretary, LaHood was at the center of efforts to reduce fatigue among pilots and called for greater investment in high-speed rail. He also pushed for large fines against Toyota for safety problems and for a new transportation bill in Congress.

“We have made great progress in improving the safety of our transit systems, pipelines, and highways, and in reducing roadway fatalities to historic lows,” he said. “We have strengthened consumer protections with new regulations on buses, trucks, and airlines.”

In a statement, Obama praised LaHood, the last remaining Republican from the president’s first-term Cabinet, as a public servant who has been more interested in practical solutions than in partisan politics.

Several people have been mentioned as possible replacements for LaHood. Among them: Antonio Villaraigosa, the Democratic mayor of Los Angeles; Ed Rendell, the former governor of Pennsylvania; Debbie Hersman, the chairwoman of the National Transportation Safety Board; and Jennifer Granholm, the former Democratic governor of Michigan.