NHTSA Proposes a New FMVSS for Electronic Stability Control Systems for Heavy Vehicles
On May 23, 2012, NHTSA published a notice of proposed rulemaking (NPRM) (Vol. 77, Number 100; Docket No.NHTSA-2012-0065) which proposes to add 49CFR Part 571 FMVSS 136 - Electronic Stability Control Systems for Heavy Vehicles. This proposal aims to require electronic stability control (ESC) systems on truck tractors and certain buses with a gross vehicle weight rating of greater than 11,793 kilograms (26,000 pounds). ESC systems in truck tractors and large buses are designed to reduce untripped rollovers and mitigate severe understeer or oversteer conditions that lead to loss of control by using automatic computer-controlled braking and reducing engine torque output. NHTSA expects that about 26% of new truck tractors and 80% of buses affected by this proposal will be equipped with ESC in 2012. They believe that ESC systems could prevent 40-65% of untripped rollover crashes and 14% of loss of control crashes (1,807-2,329 crashes, 649-858 injuries and 49-60 fatalities).
The ESC systems meeting the equipment and performance criteria of this proposed standard would use engine torque control and computer-controlled braking of individual wheels to assist the driver in maintaining control of the vehicle and maintaining its heading in situations in which the vehicle is becoming roll unstable (i.e., wheel lift potentially leading to rollover) or experiencing loss of control (i.e., deviation from driver’s intended path due to understeer, oversteer, trailer swing or any other yaw motion leading to directional loss of control). In such situations, intervention by the ESC system can assist the driver in maintaining control of the vehicle, thereby preventing fatalities and injuries associated with vehicle rollover or collision.
If finalized as proposed, the following actions would result:
- ESC system must meet both definitional criteria and performance requirements. Definitional criteria is necessary because developing separate performance tests to cover the wide array of possible operating ranges, roadways, and environmental conditions would be impractical. The definitional criteria are consistent with those recommended by SAE International and used by the United Nations (UN) Economic Commission for Europe (ECE), and similar to the definition of ESC in FMVSS No. 126.
- System able to detect ESC malfunction and provide driver notification.
- No provision for ESC deactivation (i.e., no on/off switch).
- Based on testing at VRTC and results from industry provided test data, two stability proposed performance tests have been chosen to evaluate ESC systems on truck tractors and large buses - sine with dwell (SWD) and slowly increasing steer (SIS).
- Effective date for most truck tractors and covered buses is two years after Final Rule; Two additional years for 3-axle tractors w/ one drive axle, tractors w/4 or more axles and severe service tractors.
NHTSA is requesting comments on certain aspects of this NPRM. Some of the items include, but are not limited to:
- Whether this proposal should be applied to the types of buses that are excluded from the proposed rule such as school buses and transit buses. Feasibility of including the Class 7 buses built on chassis similar to those of single unit trucks within two years. In particular, NHTSA believes that ESC systems are readily available for air-braked buses; however, system availability for any hydraulically braked buses that may be covered by this proposed rule may be more limited. If hydraulically braked buses are covered by this proposal, NHTSA requests comment on manners in which hydraulically braked buses may be differentiated for exclusion or a different phase-in period.
- Complexity of the single unit truck population and the limited crash data available present a significant challenge to determining the effectiveness of stability control on these vehicles. NHTSA believes that approximately 1 percent of newly manufactured single-unit trucks are equipped with stability control systems, and that few, if any, of those are for vehicles with hydraulic brakes. Because NHTSA is concerned about the availability of production-ready systems on these vehicles, they are not included in the proposal. However, NHTSA seeks comment on these observations.
- This NPRM does not propose requiring truck tractors, trailers, or large buses to be equipped with stability control systems "subsequent to initial manufacture", NHTSA is requesting public comment on issues related to retrofitting in-service truck tractors, trailers, and buses.
- Heavy vehicles currently equipped with ESC systems do not include on/off controls for ESC that would allow a driver to deactivate or adjust the ESC system. NHTSA did not propose to allow an on/off switch for ESC systems in this NPRM. Nevertheless, they seek comment on the need to allow an on/off switch.
- The agency is requesting comment on whether there is a safety need for an ESC activation indicator.
- NHTSA requests comments on testing. Some of the areas mentioned include: Issues related to the RSM and J-turn tests - including test conditions, steering input method, and performance; NPRM's lack of a proposed understeer test; the necessity of the use of anti-jackknife cables during agency compliance testing and control trailer items.
Comments for this NPRM must be received by NHTSA on or before August 21, 2012. NHTSA plans to hold a public hearing during the summer of 2012 - date to be published in Federal Register.