ABC News’ Rick Klein reports: With transportation policy at the forefront this week, Treasury Secretary Ray LaHood will be our guest on ABCNews.com’s “Top Line” Tuesday, at noon ET. LaHood joined President Obama and Vice President Joe Biden today in celebrating the approval of the 2,000th transportation project approved for funding under the stimulus package. It’s part of a White House campaign — part victory lap, part pep talk, part sales job — talking up the impact of the stimulus bill that the administration pressed so hard to get passed. Administration officials are casting the effort as part of the broader message of an economy on the move. LaHood this week will be visiting a series of places where shovels are hitting the ground — including Philadelphia, Providence, the New Hampshire seacoast, and Vermont. It’s a big transportation week on other fronts, too: The White House is set to unveil a new high-speech rail initiative on Thursday. But at the same time, progress on the stimulus is hard to measure. Per ABC’s Lisa Chinn: “While it is true that there are 2,000 transportation projects that have been approved by the Department of Transportation, there are not 2,000 projects underway, as the president’s remarks might lead you to believe. “That of course, begs the question: how many Recovery Act transportation projects actually have begun? The administration isn’t saying. “And furthermore, states aren’t required by law to post what they’ve actually started until October, so we won’t really know until then.” We’ll ask LaHood about all that and more Tuesday. LaHood is also playing another role for the Obama White House: envoy to the GOP. LaHood, a former Republican House member from Illinois, is serving as an unofficial go-between for the administration in its courtship of Capitol Hill Republicans. “He’s our ambassador beyond his portfolio,” White House Chief of Staff Rahm Emanuel told Tribune Co.’s Mike Dorning. Watch the interview live at noon ET at ABCNews.com.