Review of Canadian Experience with the Regulation of Large Commercial Motor Vehicles (2010) / Chapter Skim
Currently Skimming:
Appendix D - Recommended Regulatory Principles for Interprovincial Heavy Vehicle Weights and Dimensions
Appendix D - Recommended Regulatory Principles for Interprovincial Heavy Vehicle Weights and Dimensions
Pages 114-126
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 114... ...
Houston, Alberta Transportation and Utilities Preface: The report which follows constitutes the draft final report of the Implementation Planning Subcommittee of the Joint RTAC/CCMTA Committee on Heavy Vehicle Weights and Dimensions. Following the completion of the Vehicle Weights and Dimensions Research Program, marked by the delivery of the Technical Steering Committee Report in December 1986, the Implementation Planning Subcommittee was charged with the following responsibilities: 1.
|
From page 115... ...
To encourage the use of the most stable heavy vehicle configurations through the implementation of practical, enforceable weight and dimensions limits.
|
From page 116... ...
Consequently, any revision of existing limits has implications for the stability of heavy combination vehicles and for the safe operation of the highway system as a whole. 1.2 Vehicle Stability and Control Performance Criteria The extensive programs of testing and computer simulation carried out under the research program served to document the wide range of stability and control characteristics of vehicles currently found in the commercial transport fleet.
|
From page 117... ...
The Load Transfer Ratio is calculated as follows: Load Transfer Ratio = sum|FL-FR|/sum(FL+FR) where: FL = Left side tire loads FR = Right side tire loads Target Performance Level: When a vehicle in the loaded condition negotiates an obstacle avoidance, or lane change manoeuver at highway speeds, the load transfer ratio should not exceed 0.60.
|
From page 118... ...
As a consequence, the performance measure described above is somewhat theoretical in nature, and may not be easily verified through physical testing of appropriately configured vehicles. Nonetheless, the Braking Efficiency measure as determined using simulation or analysis techniques does provide a valuable, consistent basis upon which valid comparisons of the braking performance of differing vehicle configurations can be made, and provides a reasonable target performance level which vehicles in the fleet should be capable of achieving.
|
From page 119... ...
Target Performance Level: When a vehicle negotiates an obstacle avoidance, or lane change, manoeuver at highway speeds, the maximum lateral excursion of the rearmost axle of the vehicle, relative to the final lateral path displacement of the steering axle, should not exceed 0.8 m. 1.3 Regulatory Approach, Rationale and Application The regulatory principles were established on the basis of the findings of the research program and were used to select weight and dimension limits which have been developed in the context of the following objectives: 1.
|
From page 120... ...
2.0 Discussion of Proposed Regulatory Controls and Limits Vehicle stability and infrastructure impacts are influenced to varying degrees by many components of the vehicle and the physical configuration of the components. In some cases the research demonstrated a clear and significant correlation between a vehicle parameter and a performance measure, thereby providing an opportunity for effective regulatory control.
|
From page 121... ...
2.1.3 Interaxle Spacing: The research determined that vehicle stability degrades with decreasing tractor wheelbase and that a minimum spacing must be maintained between the steering axle of the tractor and the first drive axle with respect to concern for bridge distress under load. A minimum interaxle spacing requirement is proposed on the basis of encouraging the use of more stable vehicle configurations, while reducing the demands on bridge structures.
|
From page 122... ...
As wheelbases decrease, the dynamic stability degrades and the friction demands on tractor drive axles in low speed turns increase (for multiple axle semitrailers)
|
From page 123... ...
Increased axle spreads also demand higher friction levels between tractor drive axles and the road surface in tight turning manoeuvers, consequently the maximum spread which can be recommended for a tandem or tridem is also dependent on the wheelbase of the semitrailer on which it is installed. However, bridge capacity considerations require that axle spreads be increased to accept particular loading levels.
|
From page 124... ...
As this dimension increases, the dynamic stability of both A and C Train Doubles, in terms of load transfer ratio and transient high speed offtracking, degrades markedly. It is proposed that the distance from the effective turn center of the semitrailer to the location of the hitching mechanism for dolly drawbars be kept as short as possible, and be limited to a maximum of 1.8 m.
|
From page 125... ...
From the standpoint of bridge capacity constraints, there are minimum spacing requirements between axles which must be respected, regardless of vehicle configuration. It is proposed that interaxle spacings be controlled in accordance with the following table: Single Axle - Single Axle Min 3.0 m Single Axle - Tandem Axle Min 3.0 m Tandem Axle - Tandem Axle Min 5.0 m Tandem Axle - Tridem Axle Min 5.5 m Tridem Axle - Tridem Axle Min 6.0 m 2.4.2 Suspension Type and Mix: The research demonstrated that stability performance can be significantly affected by the varying characteristics of the range of suspensions commonly available to the fleet operator.
|
From page 126... ...
While no regulatory controls are proposed at this time for suspension types or mixes, it is recommended that further research be conducted in this area to determine whether regulatory controls are appropriate or warrant development. 2.4.3 Tire Type: The research demonstrated that the use of radial tires can improve the dynamic stability of heavy vehicles, particularly the double trailer configurations.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.