The Blind Men and the Elephant
And so these men of Indostan, Disputed loud and long, Each in his own opinion, Exceeding stiff and strong, Though each was partly in the right, And all were in the wrong!
There is no single classification system that can be developed for trucks.
The poem the Blind Men and the Elephant is a humorous warning that it is not possible to establish an absolute truth based on limited observations. The blind men in the poem base their understanding of the nature of an elephant on the things that they can actually observe, act like theirs is the only important observation, and then use that observation to get the nature of the elephant completely wrong.
A truck is just as complex as an elephant. If a vehicle is to be classified as a truck, and that truck was to be further classified into various types of trucks, the observations become important.
Do you classify a truck based:
- On the weight of the truck? And if weight, is it the weight at the time of the observation? Or is the maximum weight that can be legally transported? Or is it the average weight per axle?
- On the number of axles and tires of the truck?
- On the body type of the truck?
- On the length of the truck?
- On the commercial markings on the side of the truck and/or its trailer?
- On the purpose of that truck’s trip?
- On the power of the engine in the truck?
- On the type of fuel powering the truck?
- On the contents of the cargo area of the truck? If the cargo contents, how is the cargo to be classified?
These are not just idle questions. Each of these observations has been made, and the use of them leads to different and potentially incompatible classification systems. Weigh in Motion (WIM) stations observe the weight of the truck at a moment in time that it passes through that WIM Station. Departments/Registries of Motor Vehicles (DMV/RMV) report the Gross Vehicle Weight (GVW), the maximum weight of the vehicle, cargo and passengers as specified by the manufacturer of the truck. Pavement engineers are concerned with weight per axle of various types of trucks. FHWA in its Traffic Monitoring Guide (TMG) outlines a truck classification system based on the number of axles, tires and the general body type. Some state DOTs classify trucks based on the length of the truck and its trailers. Video or visual observations often classify a truck based on the marking on the side of the truck. Commercial Vehicle surveys might be the only observations of the truck purpose, and then only for the sample of trucks that are surveyed.
This can lead to classification systems that are incompatible. Both of the trucks shown below have a body type of beverage trucks. But the truck on the left would be classified by the TMG as a Class 5 (Single Unit with 2 axles and 6 tires), while the truck on the left would be a Class 8 (Combination Unit, one trailer; three axles in total). And both trucks will have a different weight per axle depending on whether they are loaded or empty.
And this does not even get at the issue of whether ANY vehicles with a GVW less than 10,000 lbs should even be called a truck. These light trucks are the subject of complex tariff systems.
(see http://www.npr.org/sections/money/2015/06/12/414029929/episode-632-the-chicken-tax,) The National Highway Traffic Safety Administration, the Federal Motor Carrier Safety Administration and the Federal Highway Administration may be too “chicken” to call light "trucks" trucks.
To paraphrase Mark Twain, there is only One True Truck Classification System.....in fact there are several of them. A truck classification system that focuses on fuel type won’t serve the needs of pavement engineers. Nor is a fuel based classification system likely to collect the axle weight data that would make it possible to develop crosswalks between those systems. It is probably unreasonable to expect to find a truck classification system that serves all needs. Just try to find ones that are useful to you.
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