After a few false alarms, Transportation Secretary Ray LaHood has finally come out and said it: He’s leaving the administration.

In a letter sent to U.S. DOT staff and contractors this morning, he listed the accomplishments of the last four years:

We have put safety front and center with the Distracted Driving Initiative and a rule to combat pilot fatigue that was decades in the making.  We have made great progress in improving the safety of our transit systems, pipelines, and highways, and in reducing roadway fatalities to historic lows.  We have strengthened consumer protections with new regulations on buses, trucks, and airlines.

We helped jumpstart the economy and put our fellow Americans back to work with $48 billion in transportation funding from the American Recovery and Investment Act of 2009, and awarded over $2.7 billion in TIGER grants to 130 transportation projects across the Nation.  We have made unprecedented investments in our nation’s ports.  And we have put aviation on a sounder footing with the FAA reauthorization, and secured funding in the Moving Ahead for Progress in the 21st Century Act to help States build and repair their roads, bridges and transit systems.

Transportation reformers would add to that list LaHood’s support for intercity rail and active transportation. Throughout his tenure he has made the case for investing in bicycling (sometimes while standing on a table), high-speed rail, and livability initiatives through the TIGER grant program.

LaHood had said in the fall of 2011 that he didn’t intend to stay for a second term, but he’d since backpedaled. Insiders said he may not have meant to make any definitive statements and was still deciding what to do. He’s told the AP that he liked working for President Obama and considered it the “best job I’ve ever had in public service” — a sentiment he repeated in his letter this morning.

LaHood said he plans “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.” The AP said a successor is expected to be confirmed by the Senate in about two months.

Now the guessing turns to who will be the next to direct U.S. DOT.

Some transportation experts have told Streetsblog they expected LaHood to step down but that they were hoping he would exit later in the second term, at a time when there’s less attention on Cabinet nominees and politics is less of a factor. Later on, they say, the Obama administration would be more likely to choose a replacement with deep, technical knowledge of transportation, rather than someone who checks the right box — a Republican, or a person of color, for example.

There has already been significant speculation over who might take over from LaHood (and Streetsblog readers have weighed in on who should get the job). The candidates include NYC DOT Commissioner Janette Sadik-Khan, outgoing L.A. Mayor Antonio Villaraigosa, and former Representative Steve LaTourette, an Ohio Republican with a track record of bi-partisan cooperation, in the LaHood mold. Former House Transportation Committee Chair Jim Oberstar recently told Politico that he was interested.

It’s time for the betting to begin in earnest.