49 CFR § 571.136 - Standard No. 136; Electronic stability control systems for heavy vehicles.
S2 Purpose. The purpose of this standard is to reduce crashes caused by rollover or by directional loss-of-control.
S3 Application. This standard applies to the following vehicles:
S3.1 Truck tractors with a gross vehicle weight rating of greater than 11,793 kilograms (26,000 pounds). However, it does not apply to:
(b) Any truck tractor that has a speed attainable in 3.2 km (2 miles) of not more than 53 km/h (33 mph); and
(c) Any truck tractor that has a speed attainable in 3.2 km (2 miles) of not more than 72 km/h (45 mph), an unloaded vehicle weight that is not less than 95 percent of its gross vehicle weight rating, and no capacity to carry occupants other than the driver and operating crew.
S3.2 Buses with a gross vehicle weight rating of greater than 11,793 kilograms (26,000 pounds). However, it does not apply to
(e) Any bus that has a speed attainable in 3.2 km (2 miles) of not more than 53 km/h (33 mph.)
Ackerman Steer Angle means the angle whose tangent is the wheelbase divided by the radius of the turn at a very low speed.
Electronic stability control system or ESC system means a system that has all of the following attributes:
(1) It augments vehicle directional stability by having the means to apply and adjust the vehicle brake torques individually at each wheel position on at least one front and at least one rear axle of the truck tractor or bus to induce correcting yaw moment to limit vehicle oversteer and to limit vehicle understeer;
(2) It enhances rollover stability by having the means to apply and adjust the vehicle brake torques individually at each wheel position on at least one front and at least one rear axle of the truck tractor or bus to reduce lateral acceleration of a vehicle;
(3) It is computer-controlled with the computer using a closed-loop algorithm to induce correcting yaw moment and enhance rollover stability;
(4) It has a means to determine the vehicle's lateral acceleration;
(5) It has a means to determine the vehicle's yaw rate and to estimate its side slip or side slip derivative with respect to time;
(6) It has a means to estimate vehicle mass or, if applicable, combination vehicle mass;
(7) It has a means to monitor driver steering inputs;
ESC service brake application means the time when the ESC system applies a service brake pressure at any wheel for a continuous duration of at least 0.5 second of at least 34 kPa (5 psi) for air-braked systems and at least 172 kPa (25 psi) for hydraulic-braked systems.
Lateral acceleration means the component of the vector acceleration of a point in the vehicle perpendicular to the vehicle x-axis (longitudinal) and parallel to the road plane.
Peak friction coefficient or PFC means the ratio of the maximum value of braking test wheel longitudinal force to the simultaneous vertical force occurring prior to wheel lockup, as the braking torque is progressively increased.
Perimeter-seating bus means a bus with 7 or fewer designated seating positions rearward of the driver's seating position that are forward-facing or can convert to forward-facing without the use of tools and is not an over-the-road bus.
Side slip or side slip angle means the arctangent of the lateral velocity of the center of gravity of the vehicle divided by the longitudinal velocity of the center of gravity.
Snub means the braking deceleration of a vehicle from a higher speed to a lower speed that is greater than zero.
Stop-request system means a vehicle-integrated system for passenger use to signal to a vehicle operator that they are requesting a stop.
Tandem axle means a group or set of two or more axles placed in close arrangement, one behind the other, with the centerlines of adjacent axles not more than 72 inches apart.
Wheelbase means the longitudinal distance between the center of the front axle and the center of the rear axle. For vehicles with tandem axles, the center of the axle is the midpoint between the centers of the most forward and most rearward tandem axles, measured when all liftable axles are in the lowered position.
Yaw Rate means the rate of change of the vehicle's heading angle measure in degrees per second of rotation about a vertical axis through the vehicle's center of gravity.
S5 Requirements. Each vehicle must be equipped with an ESC system that meets the requirements specified in S5 under the test conditions specified in S6 and the test procedures specified in S7 of this standard.
S5.1 Required Equipment. Each vehicle to which this standard applies must be equipped with an electronic stability control system, as defined in S4.
S5.2 System Operational Capabilities.
S5.2.1 The ESC system must be operational over the full speed range of the vehicle except at vehicle speeds less than 20 km/h (12.4 mph), when being driven in reverse, or during system initialization.
S5.3 Performance Requirements.
S5.3.1 Lane Keeping During Reference Speed Determination. During each series of four consecutive test runs conducted at the same entrance speed as part of the test procedure to determine the Preliminary Reference Speed and the Reference Speed (see S7.7.1), the wheels of the truck tractor or bus must remain within the lane between the start gate (0 degrees of radius arc angle) and the end gate (120 degrees of radius arc angle) during at least two of the four test runs.
S5.3.2 Engine Torque Reduction. During each series of four consecutive test runs for the determination of engine torque reduction (see S7.7.2), the vehicle must satisfy the criteria of S184.108.40.206 and S220.127.116.11 during at least two of the four test runs.
S18.104.22.168 The ESC system must reduce the driver-requested engine torque by at least 10 percent for a minimum continuous duration of 0.5 second during the time period from 1.5 seconds after the vehicle crosses the start gate (0 degree of radius arc angle) to when it crosses the end gate (120 degrees of radius arc angle).
S5.3.3 Roll Stability Control Test. During each series of eight consecutive test runs for the determination of roll stability control (see S7.7.3) conducted at the same entrance speed, the vehicle must satisfy the criteria of S22.214.171.124, S126.96.36.199, S188.8.131.52, and S184.108.40.206 during at least six of the eight consecutive test runs.
S220.127.116.11 The vehicle speed measured at 3.0 seconds after vehicle crosses the start gate (0 degrees of radius arc angle) must not exceed 47 km/h (29 mph).
S18.104.22.168 The vehicle speed measured at 4.0 seconds after vehicle crosses the start gate (0 degrees of radius arc angle) must not exceed 45 km/h (28 mph).
S5.4 ESC Malfunction Detection. Each vehicle must be equipped with an indicator lamp, mounted in front of and in clear view of the driver, which is activated whenever there is a malfunction that affects the generation or transmission of control or response signals in the vehicle's electronic stability control system.
S5.4.1 Except as provided in S5.4.3 and S5.4.6, the ESC malfunction telltale must illuminate only when a malfunction exists and must remain continuously illuminated for as long as the malfunction exists, whenever the ignition locking system is in the “On” (“Run”) position.
S5.4.2 The ESC malfunction telltale must be identified by the symbol shown for “Electronic Stability Control System Malfunction” or the specified words or abbreviations listed in Table 1 of Standard No. 101 (§ 571.101).
S5.4.3 The ESC malfunction telltale must be activated as a check-of-lamp function either when the ignition locking system is turned to the “On” (“Run”) position when the engine is not running, or when the ignition locking system is in a position between the “On” (“Run”) and “Start” that is designated by the manufacturer as a check-light position.
S5.4.4 The ESC malfunction telltale need not be activated when a starter interlock is in operation.
S6 Test Conditions. The requirements of S5 must be met by a vehicle when it is tested according to the conditions set forth in the S6, without replacing any brake system part or making any adjustments to the ESC system except as specified. On vehicles equipped with automatic brake adjusters, the automatic brake adjusters will remain activated at all times.
S6.1 Ambient Conditions.
S6.1.1 The ambient temperature is any temperature between 2 °C (35 °F) and 40 °C (104 °F).
S6.1.2 The maximum wind speed is no greater than 5 m/s (11 mph).
S6.2 Road Test Surface.
S6.2.1 The tests are conducted on a dry, uniform, solid-paved surface. Surfaces with irregularities and undulations, such as dips and large cracks, are unsuitable.
S6.2.2 The road test surface produces a peak friction coefficient (PFC) of 0.9 when measured using an American Society for Testing and Materials (ASTM) E1136-93 (Reapproved 2003) standard reference test tire, in accordance with ASTM Method E 1337-90 (Reapproved 2008), at a speed of 64.4 km/h (40 mph), without water delivery (both documents incorporated by reference, see § 571.5).
S6.2.3 The test surface has a consistent slope between 0% and 1%.
S6.2.4 J-Turn Test Maneuver Test Course. The test course for the J-Turn test maneuver is used for the Reference Speed Test in S7.7.1, the Engine Torque Reduction Test in S7.7.2, and the Roll Stability Control Test in S7.7.3.
S22.214.171.124 The test course consists of a straight entrance lane with a length of 22.9 meters (75 feet) tangentially connected to a curved lane section with a radius of 45.7 meters (150 feet) measured from the center of the lane.
S126.96.36.199 For truck tractors, the lane width of the test course is 3.7 meters (12 feet). At the manufacturer's option, for truck tractors with a wheelbase equal to or greater than 7112 mm (280 inches) the lane width of the test course is 3.7 meters (12 feet) for the straight section and is 4.3 meters (14 feet) for the curved section. For buses, the lane width of the test course is 3.7 meters (12 feet) for the straight section and is 4.3 meters (14 feet) for the curved section.
S188.8.131.52 The start gate is the tangent point on the radius (the intersection of the straight lane and the curved lane sections) and is designated as zero degrees of radius of arc angle. The end gate is the point on the radius that is 120 degrees of radius arc angle measured from the tangent point.
S184.108.40.206 Figure 1 shows the test course with the curved lane section configured in the counter-clockwise steering direction relative to the entrance lane. The course is also arranged with the curved lane section configured in the clockwise steering direction relative to the entrance lane. The cones depicted in Figure 1 defining the lane width are positioned solely for illustrative purposes.
S6.3 Vehicle Conditions.
S6.3.1 The ESC system is enabled for all testing, except for the ESC malfunction test (see S7.8).
S6.3.2 All vehicle openings (doors, windows, hood, trunk, cargo doors, etc.) are in a closed position except as required for instrumentation purposes.
S6.3.3 Test Weight.
S220.127.116.11 Truck Tractors. A truck tractor is loaded to its GVWR by coupling it to a control trailer (see S6.3.5). The tractor is loaded with the test driver, test instrumentation, and an anti-jackknife system (see S6.3.8).
S18.104.22.168 Buses. A bus is loaded with ballast (weight) to its GVWR to simulate a multi-passenger and baggage configuration. For this configuration the bus is loaded with test driver, test instrumentation, outriggers (see S6.3.6), ballast, and a simulated occupant in each of the vehicle's designated seating positions. The simulated occupant loads are attained by securing 68 kilograms (150 pounds) of ballast in each of the test vehicle's designated seating positions. If the simulated occupant loads result in the bus being loaded to less than its GVWR, additional ballast is added to the bus in the following manner until the bus is loaded to its GVWR without exceeding any axle's GAWR: First, ballast is added to the lowest baggage compartment; second, ballast is added to the floor of the passenger compartment. If the simulated occupant loads result in the GAWR of any axle being exceeded or the GVWR of the bus being exceeded, simulated occupant loads are removed until the vehicle's GVWR and all axles' GAWR are no longer exceeded.
S6.3.4 Transmission and Brake Controls. The transmission selector control is in a forward gear during all maneuvers. A vehicle equipped with an engine braking system that is engaged and disengaged by the driver is tested with the system disengaged.
S6.3.5 Control Trailer.
S22.214.171.124 The control trailer is an unbraked, flatbed semi-trailer that has a single axle with a GAWR of 8,165 kg (18,000 lb.). The control trailer has a length of at least 6,400 mm (252 inches), but no more than 7,010 mm (276 inches), when measured from the transverse centerline of the axle to the centerline of the kingpin (the point where the trailer attaches to the truck tractor). At the manufacturer's option, truck tractors with four or more axles may use a control trailer with a length of more than 7,010 mm (276 inches), but no more than 13,208 mm (520 inches) when measured from the transverse centerline of the axle to the centerline of the kingpin.
S126.96.36.199 The location of the center of gravity of the ballast on the control trailer is directly above the kingpin. The height of the center of gravity of the ballast on the control trailer is less than 610 mm (24 inches) above the top of the tractor's fifth-wheel hitch (the area where the truck tractor attaches to the trailer).
S188.8.131.52 A truck tractor is loaded to its GVWR by placing ballast (weight) on the control trailer which loads the tractor's non-steer axles. The control trailer is loaded with ballast without exceeding the GAWR of the trailer axle. If the tractor's fifth-wheel hitch position is adjustable, the fifth-wheel hitch is adjusted to proportionally distribute the load on each of the tractor's axle(s), according to each axle's GAWR, without exceeding the GAWR of any axle(s). If the fifth-wheel hitch position cannot be adjusted to prevent the load from exceeding the GAWR of the tractor's axle(s), the ballast is reduced until the axle load is equal to or less than the GAWR of the tractor's rear axle(s), maintaining load proportioning as close as possible to specified proportioning.
S6.3.6 Outriggers. Outriggers are used for testing each vehicle. The outriggers are designed with a maximum weight of 1,134 kg (2,500 lb.), excluding mounting fixtures.
S6.3.7 Tires. The tires are inflated to the vehicle manufacturer's specified pressure for the GVWR of the vehicle.
S6.3.8 Truck Tractor Anti-Jackknife System. A truck tractor is equipped with an anti-jackknife system that allows a minimum articulation angle of 30 degrees between the tractor and the control trailer.
S6.3.10 Liftable Axles. A vehicle with one or more liftable axles is tested with the liftable axles down.
S6.3.12 Thermocouples. The brake temperature is measured by plug-type thermocouples installed in the approximate center of the facing length and width of the most heavily loaded shoe or disc pad, one per brake. A second thermocouple may be installed at the beginning of the test sequence if the lining wear is expected to reach a point causing the first thermocouple to contact the rubbing surface of a drum or rotor. The second thermocouple is installed at a depth of 0.080 inch and located within 1.0 inch circumferentially of the thermocouple installed at 0.040 inch depth. For center- grooved shoes or pads, thermocouples are installed within 0.125 inch to 0.250 inch of the groove and as close to the center as possible.
S6.4 Selection of Compliance Options. Where manufacturer options are specified, the manufacturer must select the option by the time it certifies the vehicle and may not thereafter select a different option for the vehicle. Each manufacturer shall, upon request from the National Highway Traffic Safety Administration, provide information regarding which of the compliance options it has selected for a particular vehicle or make/model.
S7 Test Procedure. S7.1 Tire Inflation. Inflate the vehicle's tires as specified in S6.3.7.
S7.2 Telltale Lamp Check. With the vehicle stationary and the ignition locking system in the “Lock” or “Off” position, activate the ignition locking system to the “On” (“Run”) position or, where applicable, the appropriate position for the lamp check. The ESC system must perform a check-of-lamp function for the ESC malfunction telltale, as specified in S5.4.3.
S7.3 Tire Conditioning. Condition the tires to wear away mold sheen and achieve operating temperature immediately before beginning the J-Turn test runs. The test vehicle is driven around a circle 150 feet (46 meters) in radius at a speed that produces a lateral acceleration of approximately 0.1g for two clockwise laps followed by two counterclockwise laps.
S7.4 Brake Conditioning and Temperature. Conditioning and warm-up of the vehicle brakes are completed before and monitored during the execution of the J-Turn test maneuver.
S7.4.1 Brake Conditioning. Condition the brakes in accordance with S184.108.40.206 and S220.127.116.11.
S18.104.22.168 Prior to executing the J-Turn test maneuver, the vehicle's brakes are burnished as follows: With the transmission in the highest gear appropriate for a speed of 64 km/h (40 mph), make 500 snubs between 64 km/h (40 mph) and 32 km/h (20 mph) at a deceleration rate of 0.3g, or at the vehicle's maximum deceleration rate if less than 0.3g. After each brake application accelerate to 64 km/h (40 mph) and maintain that speed until making the next brake application at a point 1.6 km (1.0 mile) from the initial point of the previous brake application. If the vehicle cannot attain a speed of 64 km/h (40 mph) in 1.6 km (1.0 mile), continue to accelerate until the vehicle reaches 64 km/h (40 mph) or until the vehicle has traveled 2.4 km (1.5 miles) from the initial point of the previous brake application, whichever occurs first. The brakes may be adjusted up to three times during the burnish procedure, at intervals specified by the vehicle manufacturer, and may be adjusted at the conclusion of the burnishing, in accordance with the vehicle manufacturer's recommendation.
S22.214.171.124 Prior to executing the performance tests in S7.7, the brakes are conditioned using 40 brake application snubs from a speed of 64 km/h (40 mph) to a speed of 32 km/h (20 mph), with a target deceleration of approximately 0.3g. After each brake application, accelerate to 64 km/h (40 mph) and maintain that speed until making the next brake application at a point 1.6 km (1.0 mile) from the initial point of the previous brake application.
S7.4.2 Brake Temperature. Prior to testing or any time during testing, if the hottest brake temperature is above 204 °C (400 °F) a cool down period is performed until the hottest brake temperature is measured within the range of 66 °C-204 °C (150 °F-400 °F). Prior to testing or any time during testing, if the hottest brake temperature is below 66 °C (150 °F) individual brake stops are repeated to increase any one brake temperature to within the target temperature range of 66 °C-204 °C (150 °F-400 °F) before a test maneuver is performed.
S7.5 Mass Estimation Cycle. Perform the mass estimation procedure for the ESC system according to the manufacturer's instructions. This procedure will be repeated if an ignition cycle occurs or is needed at any time between the initiation and completion of S7.7.
S7.6 ESC System Malfunction Check. Check that the ESC system is enabled by ensuring that the ESC malfunction telltale is not illuminated.
S7.7 J-Turn Test Maneuver. The truck tractor or bus is subjected to multiple series of test runs using the J-Turn test maneuver. The truck tractor or bus travels through the course by driving down the entrance lane, crossing the start gate at the designated entrance speed, turning through the curved lane section, and crossing the end gate, while the driver attempts to keep all of the wheels of the truck tractor or bus within the lane.
S7.7.1 Reference Speed Test. The vehicle is subjected to J-Turn test maneuvers to determine the Reference Speed for each steering direction. The Reference Speeds are used in S7.7.2 and S7.7.3.
S126.96.36.199 Preliminary Reference Speed Determination. The vehicle is subjected to two series of test runs using the J-Turn test maneuver at increasing entrance speeds. One series uses clockwise steering, and the other series uses counterclockwise steering. The entrance speed of a test run is the 0.5 second average of the raw speed data prior to any ESC system activation of the service brakes and rounded to the nearest 1.0 mph. During each test run, the driver attempts to maintain the selected entrance speed throughout the J-Turn test maneuver. For the first test run of each series, the entrance speed is 32 km/h ±1.6 km/h (20 mph ±1.0 mph) and is incremented 1.6 km/h (1.0 mph) for each subsequent test run until ESC service brake application occurs or any of the truck tractor's or bus's wheels departs the lane. The vehicle entrance speed at which ESC service brake application occurs is the Preliminary Reference Speed. The Preliminary Reference Speed is determined for each direction: Clockwise steering and counter-clockwise steering. During any test run, if any of the wheels of the truck tractor or bus depart the lane at any point within the first 120 degrees of radius arc angle, the test run is repeated at the same entrance speed. If any of the wheels of the truck tractor or bus depart the lane again, then four consecutive test runs are repeated at the same entrance speed (±1.6 km/h (±1.0 mph)).
S188.8.131.52 Reference Speed Determination. Using the Preliminary Reference Speed determined in S184.108.40.206, perform two series of test runs using the J-Turn test maneuver to determine the Reference Speed. The first series consists of four consecutive test runs performed using counter-clockwise steering. The second series consists of four consecutive test runs performed using clockwise steering. During each test run, the driver attempts to maintain a speed equal to the Preliminary Reference Speed throughout the J-Turn test maneuver. The Reference Speed is the minimum entrance speed at which ESC service brake application occurs for at least two of four consecutive test runs of each series conducted at the same entrance speed (within ±1.6 km/h (±1.0 mph)). The Reference Speed is determined for each direction: clockwise steering and counter-clockwise steering. If ESC service brake application does not occur during at least two test runs of either series, the Preliminary Reference Speed is increased by 1.6 km/h (1.0 mph), and the procedure in this section is repeated.
S7.7.2 Engine Torque Reduction Test. The vehicle is subjected to two series of test runs using the J-Turn test maneuver at an entrance speed equal to the Reference Speed determined in S220.127.116.11. One series uses clockwise steering, and the other series uses counter-clockwise steering. Each series consists of four test runs with the vehicle at an entrance speed equal to the Reference Speed and the driver fully depressing the accelerator pedal from the time when the vehicle crosses the start gate until the vehicle reaches the end gate. ESC engine torque reduction is confirmed by comparing the engine torque output and driver requested torque data collected from the vehicle communication network or CAN bus. During the initial stages of each maneuver the two torque signals with respect to time will parallel each other. Upon ESC engine torque reduction, the two signals will diverge when the ESC system causes a commanded engine torque reduction and the driver depresses the accelerator pedal attempting to accelerate the vehicle.
S18.104.22.168 Perform two series of test runs using the J-Turn test maneuver at the Reference Speed determined in S22.214.171.124 (±1.6 km/h (±1.0 mph)). The first series consists of four consecutive test runs performed using counter-clockwise steering. The second series consists of four consecutive test runs performed using clockwise steering. During each test run, the driver fully depresses the accelerator pedal from the time when the vehicle crosses the start gate until the vehicle reaches the end gate.
S126.96.36.199 During each of the engine torque reduction test runs, verify the commanded engine torque and the driver requested torque signals diverge according to the criteria specified in S188.8.131.52.
S7.7.3 Roll Stability Control Test. The vehicle is subjected to multiple series of test runs using the J-Turn test maneuver in both the clockwise and the counter-clockwise direction.
S184.108.40.206 Before each test run, the brake temperatures are monitored and the hottest brake is confirmed to be between 66 °C (150 °F) and 204 °C (400 °F). If the hottest brake temperature is not between 66 °C (150 °F) and 204 °C (400 °F), the brake temperature is adjusted in accordance with S7.4.2.
S220.127.116.11 During each test run, the driver will release the accelerator pedal after the ESC system has slowed vehicle by more than 4.8 km/h (3.0 mph) below the entrance speed.
S18.104.22.168 The maximum test speed is the greater of 130 percent of the Reference Speed (see S22.214.171.124) or 48 km/h (30 mph). The maximum test speed is determined for each direction: clockwise steering and counter-clockwise steering.
S126.96.36.199 For each series of Roll Stability Control test runs, the vehicle will perform eight consecutive test runs at the same entrance speed, which is any speed between 48 km/h (30 mph) and the maximum test speed determined according to S188.8.131.52.
S184.108.40.206 Upon completion of testing, post processing is done as specified in S7.9.
S7.8 ESC Malfunction Detection.
S7.8.1 Simulate one or more ESC malfunction(s) by disconnecting the power source to any ESC component, or disconnecting any electrical connection between ESC components (with the vehicle power off). When simulating an ESC malfunction, the electrical connections for the telltale lamp(s) are not disconnected.
S7.8.2 With the vehicle initially stationary and the ignition locking system in the “Lock” or “Off” position, activate the ignition locking system to the “Start” position and start the engine. Place the vehicle in a forward gear and accelerate to 48 ±8 km/h (30 ±5 mph). Drive the vehicle for at least two minutes including at least one left and one right turning maneuver and at least one service brake application. Verify that, within two minutes of attaining this speed, the ESC malfunction indicator illuminates in accordance with S5.4.
S7.8.3 Stop the vehicle, deactivate the ignition locking system to the “Off” or “Lock” position. After a five-minute period, activate the vehicle's ignition locking system to the “Start” position and start the engine. Verify that the ESC malfunction indicator again illuminates to signal a malfunction and remains illuminated as long as the engine is running until the fault is corrected.
S7.8.4 Deactivate the ignition locking system to the “Off” or “Lock” position. Restore the ESC system to normal operation, activate the ignition system to the “Start” position and start the engine. Verify that the telltale has extinguished.
S7.9 Post Data Processing.
S7.9.1 Raw vehicle speed data is filtered with a 0.1 second running average filter.
S7.9.2 The torque data collected from the vehicle communication network or CAN bus as a digital signal does not get filtered. The torque data collected from the vehicle communication network or CAN bus as an analog signal is filtered with a 0.1-second running average.
S7.9.3 The activation point of the ESC engine torque reduction is the point where the measured driver demanded torque and the engine torque first begin to deviate from one another (engine torque decreases while the driver requested torque increases) during the Engine Torque Reduction Test. The torque values are obtained directly from the vehicle communication network or CAN bus. Torque values used to determine the activation point of the ESC engine torque reduction are interpolated.
S7.9.4 The time measurement for the J-Turn test maneuver is referenced to “time zero”, which is defined as the instant the center of the front tires of the vehicle reach the start gate, the line within the lane at zero degrees of radius arc angle. The completion of the maneuver occurs at the instant the center of the front tires of the vehicle reach the end gate, which is the line within the lane at 120 degrees of radius arc angle.
S7.9.5 Raw service brake pressure measurements are zeroed (calibrated). Zeroed brake pressure data are filtered with 0.1 second running average filters. Zeroed and filtered brake pressure data are dynamically offset corrected using a defined “zeroed range”. The “zeroing range” is defined as the 0.5 second time period prior to “time zero” defined in S7.9.4.
S8.1.1 All buses with a gross vehicle weight rating of greater than 14,969 kilograms (33,000 pounds) manufactured on or after June 24, 2018 must comply with this standard.
S8.1.2 All buses manufactured on or after August 1, 2019 must comply with this standard.
S8.2.1 All three-axle truck tractors with a front axle that has a GAWR of 6,622 kilograms (14,600 pounds) or less and with two rear drive axles that have a combined GAWR of 20,412 kilograms (45,000 pounds) or less manufactured on or after August 1, 2017 must comply with this standard.
S8.2.2 All truck tractors manufactured on or after August 1, 2019 must comply with this standard.