NTSB Number: SS-92/01
NTIS Number: PB92-917003

The Safety Board developed two data sources in support of this study. Over a 17-month period, the Safety Board investigated selected brake-related accidents involving heavy trucks and buses. In addition, an extensive program to inspect heavy trucks was conducted in five States. This inspection program enabled the Safety Board to assess the mechanical condition of heavy truck brake systems.

The Safety Board also used several national and State data sources in support of this study. Data sources on heavy vehicle accidents were analyzed to identify the scope of brake-related accidents as well as the potential costs to society associated with such accidents. The analysis indicated that this type of accident may be substantially underrepresented in the available data sources, primarily because of underreporting by investigating agencies.

The accident and inspection data highlighted three safety problems. First, it is difficult to keep the brakes found on most commercial vehicles adjusted appropriately; these brakes have only a small tolerance range before becoming out of adjustment. Second, most brakes on heavy vehicles are not well maintained, often resulting in out-of-adjustment brakes. Third, the accident investigations illustrated that brake system components were factors in certain vehicle instability accidents.

As a result of this study, recommendations were issued to the National Highway Traffic Safety Administration, the Federal Highway Administration, the 50 States and the District of Columbia, the Interstate Towing Association, the Towing and Recovery Association of America, the National Private Truck Council, the Owner-Operator Independent Drivers Association, the American Trucking Associations, the Motor Vehicle Manufacturers Association, the Professional Truck Driver Institute of America, the Society of Automotive Engineers, and airbrake component manufacturers.

RECOMMENDATIONS

As a result of this safety study, the National Transportation Safety Board made the following recommendations:

to the National Highway Traffic Safety Administration:

Require that air-braked vehicles be equipped with visible adjustment indicators that will allow one person to check the level of adjustment. (Class II, Priority Action) (H-92-50)

Expedite the proposed rulemaking to require automatic adjusters on vehicles equipped with airbrake systems. (Class II, Priority Action) (H-92-51)

Adopt braking performance regulations that restrict the general use of automatic limiting valves on steering axle brakes of vehicles equipped with airbrake systems. (Class II, Priority Action) (H-92-52)

Adopt performance standards for vehicles equipped with airbrake systems that require stopping performance criteria on varying friction surfaces, with varying loading conditions for both straight and curved sections of roadways. (Class II, Priority Action) (H-92-53)

Require through a performance standard the use of antilock braking systems on all newly manufactured vehicles with airbrake systems. (Class II, Priority Action) (H-92-54)

Promote, in conjunction with the Federal Highway Administration, the development and use of hardware, such as the roller dynamometer, capable of measuring the braking capability of a heavy vehicle at roadside inspection facilities. (Class II, Priority Action) (H-92-55)

to the Federal Highway Administration:

Develop adequate performance criteria for allowable combinations (brake size, lining friction, and axle rating) of airbrake system components on heavy vehicles, and prohibit the use of component combinations that do not meet the criteria. (Class II, Priority Action) (H-92-56)

Encourage the installation of visible brake adjustment indicators on all vehicles equipped with airbrake systems for easy detection of adjustment levels. (Class II, Priority Action) (H-92-57)

Promote, in conjunction with the National Highway Traffic Safety Administration, the development and use of hardware, such as the roller dynamometer, Capable of measuring the braking capability of a heavy vehicle at roadside inspection facilities. (Class II, Priority Action) (H-92-59)

Review the national highway data system to ensure that sufficient data can be obtained to readily evaluate the role of braking deficiencies in commercial vehicle accidents. (Class II, Priority Action) (H-92-59)

to the 50 States, the District of Columbia, the Commonwealth of Puerto Rico, the Virgin Islands, and the Territories:

Encourage the commercial vehicle accident investigative agencies to develop policies requiring the systematic inspection of and the compilation of data from commercial vehicles that are involved in injury or fatal accidents. The policies should include inspection of brake systems and components. (Class II, Priority Action) (H-92-60)

Review the national highway data for your jurisdiction to ensure that sufficient information can be obtained to readily evaluate the role of braking deficiencies in commercial vehicle accidents. (Class II, Priority Action) (H-92-61)

In order to preserve evidence from accident investigations, require towing companies during wreckage removal to employ methods of releasing locked airbrakes that do not alter brake adjustment. (Class II, Priority Action) (H-92-62)

to the Interstate Towing Association and to the Towing and Recovery Association of America:

Encourage members to voluntarily discontinue the practice of "backing off' the airbrakes on commercial vehicles during wreckage removal operations. (Class II, Priority Action) (H-92-63)

to the National Private Truck Council:

Encourage members to use replacement parts that meet original equipment specifications (particularly brake linings and valves) when replacing brake components. (Class II, Priority Action) (H-92-64)

Encourage members to voluntarily install steering axle brakes on all heavy vehicles that currently do not have steering axle brakes. (Class II, Priority Action) (H-92-65)

Advise members about the propensity of lightly loaded combination vehicles to jackknife, especially when traveling on low-friction road surfaces. (Class II, Priority Action) (H-92-66)

Work with the American Trucking Associations to complete and distribute to member carriers appropriate brake maintenance materials that clearly establish standard inspection techniques (including adjustment indicators), inspection and adjustment interval guidelines, and an adjustment method (covering both manual and automatic slack adjusters) for S-cam brakes on heavy vehicles. Encourage members to provide a copy of the information to each driver of a heavy vehicle and to each mechanic who services heavy vehicles. (Class II, Priority Action) (H-92-67)

Encourage members to discontinue the use of the AL-Factor formula. (Class II, Priority Action) (H-92-68)

to the Owner-Operator Independent Drivers Association:

Encourage members to use replacement parts that meet original equipment specifications (particularly brake linings and valves) when replacing brake components. (Class II, Priority Action) (H-92-69)

Encourage members to voluntarily install steering axle brakes on all heavy vehicles that currently do not-have steering axle brakes. (Class II, Priority Action) (H-92-70)

Advise members about the propensity of lightly loaded combination vehicles to jackknife, especially when traveling on low friction road surfaces. (Class II, Priority Action) (H-92-71)

Work with the American Trucking Associations to complete and distribute to member carriers appropriate brake maintenance materials that clearly establish standard inspection techniques (including adjustment indicators), inspection and adjustment interval guidelines, and an adjustment method (covering both manual and automatic stack adjusters) for S-cam brakes on heavy vehicles. (Class II, Priority Action) (H-92-72)

Encourage members to discontinue the use of the AL-Factor formula. (Class II, Priority Action) (H-92-73)

to the American Trucking Associations:

Complete and distribute to member carriers appropriate brake maintenance materials that clearly establish standard inspection techniques (including adjustment indicators), inspection and adjustment interval guidelines, and an adjustment method (covering both manual and automatic slack adjusters) for S-cam brakes on heavy vehicles. Encourage members to provide a copy of the materials to each driver of a heavy vehicle and to each mechanic who services heavy vehicles. (Class II, Priority Action) (H-92-74)

Encourage members to use replacement parts that meet original equipment specifications (particularly brake linings and valves) when replacing brake components. (Class II, Priority Action) (H-92-75)

Encourage members to voluntarily install steering axle brakes on all heavy vehicles that currently do not have steering axle brakes. (Class II, Priority Action) (H-92-76)

Advise members about the propensity of lightly loaded combination vehicles to jackknife, especially when traveling on low friction road surfaces. (Class II, Priority Action) (H-92-77)

Encourage members to discontinue the use of the AL-Factor formula. (Class II, Priority Action) (H-92-78)

to the Motor Vehicle Manufacturers Association:

Encourage member manufacturers of heavy air-braked vehicles to develop, promote, and install brake systems that are less sensitive to adjustment and more resistant to brake system fade (such as long stroke chambers and air disc brakes). (Class II, Priority Action)(H-92-79)

Encourage members to discontinue the use of the AL-Factor formula. (Class II, Priority Action) (H-92-80)

to the Professional Truck Driver Institute of America:

Incorporate brake maintenance materials developed by the American Trucking Associations into a training curriculum that cautions drivers about the instabilities of lightly loaded combination vehicles when operated on low-friction road surfaces. (Class II, Priority Action) (H-92-81)

to the Society of Automotive Engineers:

Expedite the completion of Surface Vehicle Recommended Practices, SAE J1902, 'Brake Block Effectiveness Rating," and SAE J1901, 'Brake Effectiveness Marking For Brake Blocks.". (Class II, Priority Action) (H-92-92)

to airbrake component manufacturers:

Develop, promote, and install brake systems that are less sensitive to adjustment and more resistant to brake system fade (such as long stroke chambers and air disc brakes). (Class II, Priority Action) (H-92-93)

Discontinue the use of the AL-Factor formula. (Class II, Priority Action) (H-92-94)