Based at NASA's Dryden Aircraft Operations Facility in Palmdale, Calif, the ER-2 conduct high altitude earth science research; their recent tasks include studying the Deepwater Horizon oil spill. With a 105-foot wingspan, no landing gear on the wings and a pilot in a pressurized suit, the ER-2 suffers from all the same flying challenges that make the U-2 one of the most difficult-to-land aircraft in the U.S. Air Force fleet. With another set of eyes watching for complications, crashes have become far less common.
The chase vehicles, driven by pilots, speed onto the runway as the ER-2 descends, calling out readings to the ER-2 pilot so he can avoid tipping the wings into the ground or other potential problems. Just as it followed the Air Force's lead in using the chase cars for landing, NASA stuck with Detroit muscle for the task as well, leasing police-spec Chargers for the task.
Here's NASA "mobile pilot" Jan Nystrom guiding an ER-2 into a safe landing: