Standard equipment ESC would be required on passenger vehicles under 10,000 pounds starting with the 2009 model year. All new vehicles would be required to have ESC by the 2012 model year (September 2011).
The agency estimates that ESC will save between 5,300 and 10,300 lives annually and prevent between 168,000 and 252,000 injuries. The cost of adding ESC to an ABS-equipped vehicle is estimated to be $111.
The agency has been urging automakers to voluntarily add ESC to their vehicles since 2004, and almost 29 percent of 2006 light vehicles are ESC-equipped. With various manufacturers already announcing their intent to broaden the availability of ESC in their model ranges, the installation rate without the proposed regulation would increase to 71 percent in 2011.
NHTSA will allow exceptions to the new rule "for some vehicles manufactured in stages or by small volume manufacturers." In addition, an ESC "on/off" switch will be permitted to allow the driver to disable the system for special circumstances like track days, driving in deep snow and driving with mismatched tire sizes (a spacesaver spare, for example).
A new safety regulation naturally requires a new test, and the ESC will be tested using a steering robot to swerve the vehicle in a predetermined pattern while the vehicle is moving at 50 mph. According to the NHTSA, the test is severe enough to cause most vehicles to spin out without ESC.
You can download the proposed regulation and the background information here (pdf file).