WASHINGTON - US Secretary of Transportation Ray LaHood said Tuesday that he planned to step down, marking the sixth department head to leave office as President Barack Obama begins his second term.

"I have let President Obama know that I will not serve a second term as Secretary of the US Department of Transportation," Ray LaHood said in a statement, adding "I plan to stay on until my successor is confirmed to ensure a smooth transition for the Department and all the important work we still have to do."

In a statement, Obama thanked LaHood for what he's done over the last four years, saying "As Secretary of Transportation, he has fought to create jobs and grow our economy by rebuilding our roads, bridges and transit systems. Under his leadership, we have made significant investments in our passenger rail system and laid the high-speed rail network of the future."

During his tenure, LaHood has put safety front and center with the Distracted Driving Initiative and a rule to combat pilot fatigue that was decades in the making. He has also strengthened consumer protections with new regulations on buses, trucks and airlines.

Before becoming secretary in 2009, LaHood served 14 years in Congress representing an Illinois district. He's the only Republican still in Obama's Cabinet.