THE Truck Trailer Manufacturers Association has revised and reissued some key Recommended Practices (RP) and Technical Bulletins (TB) as part of a five-year review cycle of each one.
The revisions included: end dump trailer operations (clarifying means to maneuver tarps from the ground without working inside the trailer); loading and use of lowbed and industrial trailers (caution to follow manufacturers' operating instructions); trailer axle alignment (advising the use of a tape tensioner to ensure equal tension); trailer antilock braking system wiring (adding wording relating to issues about electrical power); spring parking and emergency brakes on FMVSS 121 equipped trailers (clarification regarding air supply); and trailer conspicuity systems (adding an appendix for excerpts from rulemaking and interpretations issued by the National Highway Traffic Safety Administration).
RPs are issued principally as suggested solutions to design, specification, and manufacture or testing of truck trailers and their components.
TBs are issued principally to carriers or shippers in the operation of truck trailers or to improve the serviceability or use.
Here is a review of some RPs and TBs that were either revised or reissued in May:
TB No. 74:
End Dump Trailer Operations
Originally issued May 1979; revised June 1985,November 1992, June 2000, May 2005
Purpose: To provide guidance for the safe operation of end dump trailers.
Scope: Relates to the safe operation of frameless and frame type end dump trailers.
Revisions (changes appear in italics):
Section 6.1: Tarping should be used to prevent commodities such as sand, gravel, rubbish, etc, from damaging other vehicles following the trailer. Tarping is mandatory on dumps in several states. When tarping is not used, the dump body of the vehicle should only be filled within 6 inches of the top of the side board/top rail. There are several means available for spreading and removing tarps from the ground, without requiring the operator to work on or inside the trailer. These means should be used. If a tarp has been used, it and any other accessories which might interfere with the material being dumped should be removed or retracted.
“We don't want the driver getting on top of the trailer,” says TTMA engineering manager Jeff Sims. “There have been cases where the load would shift.”
TB No. 94:
Loading and Use of Lowbed and Industrial Trailers
Originally issued December 1982; revised November 1987, February 1989; reissued October 1999; revised May 2005
Purpose: To provide some general information about the loading and use of lowbed and industrial trailers.
Scope: Intended as a general guideline only and is not to be construed as altering any ratings or loading information provided by the trailer manufacturer.
Revisions (changes appear in italics):
Section 4.1.3: When loading a lowbed trailer over the side, blocks must be placed under the side rail. This will help prevent damage to the trailer caused by undesirable twisting. If side loading is frequent, side rail will require reinforcing to reduce top flange damage. Note: Manufacturer's operating instructions and warning labels must be followed to avoid unsafe conditions during side loading.
RP No. 71-05:
Trailer Axle Alignment
Originally issued December 1984; revised June 1990, June 2000; reissued May 2005
Purpose: Intended as a guide for the alignment of axles on newly manufactured and rebuilt truck trailers.
Scope: Describes one procedure for measuring trailer axle alignment with simple tools. Other more sophisticated procedures are also acceptable.
Revisions (changes appear in italics):
Section 3.3: Proper tools for axle alignment inspection are:
A. Spring loaded, kingpin extender with bubble level.
B. Axle end extenders.
C. 50 ft steel tape. (A tape tensioner should be used with the tape to ensure equal tape tension.)
D. Adjustable tram.
E. Gauge for measuring axle center to axle center.
“We added ‘tape tensioner’ so you know you're putting the same amount of pressure on the tape,” Sims says. “If you're pulling down the right side with 5 lb, you want to make sure you're pulling down the left side with 5 lb so you're getting an even stretch on the tape.”
RP No. 97-05:
Trailer Antilock Braking System Wiring
Originally issued October 1997; revised June 1999, May 2005
Purpose: To provide guidelines for wiring a trailer antilock braking system that will comply with FMVSS 121, S5.5; to encourage a uniform method of wiring trailer ABS to enhance interchange of trailers with and without ABS.
Scope: Specifies a method of wiring the antilock braking system (ABS) on a trailer intended to be used on public roads. This RP is compatible with TTMA TB No. 119 “Electrical Interface for Truck-Trailer Interconnection,” which provides the minimum design requirements for the cables, plugs, and receptacles for the truck-trailer interconnection.
Revisions (changes appear in italics):
Section 9.1: Trailers not designed to tow another trailer (“single”): With all lamps on (including stop lamps, and one turn signal), all auxiliary devices powered that may be on as the trailer is moving, and an ABS load of 5 amperes, the voltage at the ABS ECU shall be at least 9.0 volts when the trailer is supplied power as specified in 5.1; This shall be true when the 5 ampere ABS load is applied to either the trailer stop lamp circuit or the antilock brake constant power circuit.
Section 9.2: Trailers designed to tow another trailer (“doubles” or “triples”): With all lamps of all trailers and dollies on (including stop lamps, and one turn signal), all auxiliary devices powered that may be on as the trailer is moving, and an ABS load of 10 amperes, the voltage at each ABS ECU shall be at least 9.0 volts when the lead trailer is supplied power as specified in 5.1. This shall be true when the 10 ampere ABS load is applied to either the trailer stop lamp circuit or the antilock brake constant power circuit. This performance may require the manufacturer to employ a method of limiting voltage drop such as the use of LED lights.
TB No. 70:
Spring Parking and Emergency Brakes on FMVSS 121 Equipped Trailers
Originally issued May 1976; revised July 199; reissued January 2000; revised May 2005
Purpose: To emphasize the reasons that spring brakes are installed on most trailers and the potential hazards that occur if the trailer is operated with the spring brakes caged or if servicing is attempted without caging the brakes.
Revisions (changes appear in italics):
Section 3.4: One can determine if the spring brakes are operating properly during the tractor-trailer fifth wheel-kingpin connection verification procedure. After the tractor is connected to the trailer and the trailer air reservoirs have been charged, pull the Trailer Air Supply (Trailer Emergency on pre-121 tractors) knob to evacuate the trailer air supply line. Move the tractor forward to determine if there is trailer braking resistance. If there is trailer resistance, then the trailer parking brakes are functioning and the fifthwheel has engaged the kingpin. If there is little resistance, either the trailer parking brakes are not functioning or the fifthwheel has not engaged the kingpin.
Section 4.0: Many current spring brake chambers are not designed to allow disassembly. Check with the spring brake manufacturer before attempting any service efforts. On those that can be disassembled for service, present technology provides for caging only for the occasional emergency situation. Any attempt to disassemble the spring brake component without the caging operation can result in mortal injury.
RP No. 93-05:
Trailer Conspicuity Systems
Originally issued November 1994; revised October 1999, May 2005
Purpose: To serve as a guide for installing trailer retroreflective sheeting and/or reflectors in accordance with current conspicuity system regulations of 49 CFR 571.108 (FMVSS 108) S5.7 issued by NHTSA, US Department of Transportation which became effective December 1, 1993.
Scope: Does not apply to pole trailers and converter dollies; to trailers with a GVWR of 10,000 lb or less; to trailers with a width of less than 80”; to trailers manufactured exclusively for use as offices or dwellings.
Revisions: Added Appendix A for excerpts from rulemaking and interpretations issued by NHTSA.
For more than 20 years, TTMA has issued, revised, and reissued RPs and TBs.
Through the Engineering Committee, a sub-committee reviews each one, matches it against federal regulations, and determines whether changes will be made. The document goes through a ballot and comment period, and ultimately is sent to TTMA's board of directors for approval.
TTMA president Dick Bowling stresses that judgment must be used in applying them. He refers to the “Word of Caution” that accompanies interpretations made by NHTSA: In attempting to use these interpretations to resolve a question, please be aware that they represent the views of the Chief Counsel based on the facts of individual cases at the time the letter was written. Further, interpretations that are relevant to your situation may not be available on the web site. Do not assume that the interpretation applies to your situation. Critical factual differences may exist between your situation and those addressed in previous interpretations.
“If you were to generalize and say, ‘That sounds like what I'm doing,’ it might not be specific to what you're doing because we don't see the actual question that was written to the government; we only see the answer,” Bowling says.
For complete documents, go to www.TTMAnet.org.