On April 6, 2007, the US National Highway Traffic Safety Administration (NHTSA) issued a new regulatory Final Rule (Docket No. NHTSA-2007-27662), titled FMVSS 126; Electronic Stability Control Systems, and also corresponding revisions to FMVSS 101 Controls and Displays. FMVSS 126 will require all vehicles under 10,000 lbs. to be equipped with electronic stability control (ESC) systems.
The Agency claims that ESC effectiveness is especially great for single-vehicle crashes resulting in rollover, where ESC systems are estimated to prevent 71% of passenger car rollovers, and 84% of SUV rollovers.
Based on its crash data studies and ESC performance test data, NHTSA estimates that once all light vehicles on the road have ESC systems installed, that single vehicle crashes will be reduced by 34% for passenger cars, and 59% for sport utility vehicles. NHTSA's estimates also predict that ESC will save 5,300 to 9,600 lives and prevent 156,000 to 238,000 injuries in all types of crashes annually.
Because there are technical difficulties in describing extensive objective compliance test requirements and also high test costs to manufacturers, the Agency has opted to initiate an "equipment requirement" definition, along with a simple performance test as follows:
Equipment Requirement:
These required ESC systems are to be capable of applying brake torques individually at all four wheels and to have an algorithm that utilizes this capability. Such ESC systems must also meet the following equipment requirement definitions. [based on SAE J2564 (rev. June, 2004)] :
- Ability to augment vehicle directional stability by applying and adjusting the brake torques individually to induce a correcting yaw moment;
- Is computer-controlled, with the computer using a closed-loop algorithm to limit vehicle oversteer and to limit vehicle understeer;
- Has a means to determine vehicle yaw rate and to estimate its sideslip or the time derivative of sideslip;
- Has a means to monitor driver steering input;
- Has an algorithm to determine the need, and means to modify engine torque, as necessary, to assist the driver, and
- Is operational over all speed ranges above 9.3 mph.
Performance Requirement:
NHTSA is requiring that these light vehicles shall meet a performance test when subjected to a "sine and dwell steering maneuver test" as follows:
- Coasting at an initial speed of 50 mph while a steering machine steers the vehicle with a prescribed steering wheel pattern.
- The test maneuver is then repeated over a series of increasing maximum steering angles.
NOTE: This above prescribed maneuver is severe enough to produce spinout for most vehicles without ESC. The stability criterion for the test is to measure how quickly the vehicle stops rotating after the steering wheel is returned to the straight-ahead position. A vehicle that continues to rotate for an extended period after the driver steers straight is out of control, which is what ESC is designed to prevent.
The Agency is allowing a compliance phase in period over three years as follows:
- 55% of vehicles manufactured from Sept. 1, 2008 to Aug. 31, 2009
- 75% of vehicles manufactured from Sept. 1, 2009 to Aug. 31, 2010
- 95% of vehicles manufactured from Sept. 1, 2010 to Aug. 31, 2011
- 100% of vehicles manufactured after Sept. 1, 2011
In order to achieve fleet saturation more quickly, NHTSA is not requiring vehicle manufacturers to meet the accompanying revisions to FMVSS 101 for telltales until after the phase-in period of September 1, 2011.
Carry forward credits are also available for vehicles manufactured in excess of the phase-in requirements for vehicles manufactured after June 5, 2007 and through the conclusion of the phase-in period.