Verification, Refinement, and Applicability of Long-Term Pavement Performance Vehicle Classification Rules

Chapter 9. Results From Field Testing of the Refined Vehicle Classification Rule set

Class 10

Eighteen Class 10 trucks with seven axles were observed in lane 1 during the 6-month test period. All of these trucks were correctly classified. All of them had been classified as Class 13 vehicles. In addition, three Class 10 trucks were observed with eight axles. Two of those trucks had been classified as Class 13 vehicles. The other truck had been unclassified (Class 15). Figure 33 shows a seven-axle Class 10 truck at the Maryland site.

Figure 33. Photo. Seven-axle Class 10 truck at Maryland site.

Class 13

No vehicles were observed in the test lane that fit the new LTPP Class 13 definitions during the 6-month test period at the Maryland site.

Tennessee Data

Tennessee data were available for 6 weeks: March 1 through April 15, 2012. Pictures were not available for all days during this 6-week period. The tests were therefore done by comparing data from lanes 1 and 4, even though pictures were available for only lane 4. (Note that lane 1 and lane 4 appear to be outside lanes traveling in opposite directions.)

Class 7

Data were extracted for all Class 7 trucks for the 6-week period. Fifteen Class 7 trucks with seven axles were observed. Four of those trucks had been unclassified vehicles under the old LTPP rule set (Class 15). The remaining 11 vehicles had been classified as Class 13.

In addition to those vehicles, 12 vehicles with six axles were now classified as Class 7 trucks. All of those vehicles had been unclassified (placed in Class 15) under the originally adopted LTPP algorithm.

Interestingly, all of the larger vehicles were in lane 1. None of the vehicles was in lane 4 (the opposite direction of travel), where the camera was operating, so no pictures of those vehicles were available. The assumption is that they were similar to those observed in Pennsylvania and Maryland and were equipped with drop axles. If the loaded direction was lane 1, then the trucks were operating with their lift axles in the "up" position when traveling in lane 4 and therefore were not classified as large Class 7 trucks.

All of the large Class 7 vehicles in lane 1 had similar axle configurations, including a modest distance between the first and second axles, followed by short distances between all other axles. The distances between these axles were slightly smaller than is common for quad axle spacings for five-axle Class 7 trucks at this same site. This spacing information suggests that the new LTPP WIM algorithm is working correctly.

Class 10

Because there was a very large number of "new" Class 10 vehicles at the Tennessee site, only data from the first 2 weeks of April in lane 1 and lane 4 were used to test the new Class 10 algorithm rules. During this period, 92 vehicles with eight axles and 171 vehicles with seven axles were classified as Class 10 by the new LTPP algorithm. Of those vehicles, 15 had been unclassified (Class 15), while the remaining 248 had been incorrectly classified as Class 13 under the old algorithm. All of the 96 vehicles for which images were available were correctly classified under the new algorithm.

The majority of the new Class 10 trucks consisted of a large tractor pulling a low-boy trailer with heavy equipment on it. An example of these trucks is shown in figure 34.

Figure 34. Photo. Seven-axle Class 10 truck in Tennessee.

All lane 4 vehicles were correctly classified, indicating that the new classification algorithm is working as intended.

Class 13

As with Class 10, a fairly large number of "new" Class 13 vehicles were observed at the Tennessee site. Therefore, only 2 weeks of data were used to test the new Class 13 algorithm. During this period, 77 Class 13 vehicles with 10 axles, 75 Class 13 vehicles with 11-axles, and 24 Class 13 vehicles with 12-axles were observed in lane 1, which had more large trucks than lane 4 (where the camera was located). In lane 4 (the camera lane), 36 Class 13 vehicles were observed during this same time period. Only three of those trucks had 10 or more axles and were therefore the subject of this evaluation. Consequently, the researchers also examined Class 13 vehicles in lane 4 for the 4 weeks of March. This contributed 14 additional Class 13 vehicles with 10 or more axles for visual review. All of the vehicles examined were correctly classified.

Of the vehicles reviewed, the most common Class 13 with a large number of axles was a heavy-duty, four-axle tractor pulling a low-boy trailer on an articulated support (see figure 35). These vehicles carried a variety of very heavy, non-divisible loads that ranged from M1A1 Abrams tanks, to large earth-moving equipment, to a variety of generators and other industrial machines.

Figure 35. Photo. Ten-axle Class 13 truck in Tennessee.

These trucks differed from other heavy Class 10 trucks, such as those shown in figure 34, primarily because of the extra articulated connection to the low-boy trailer. Additional examples of these different configurations can be seen in figure 36 (a Class 10 truck without the extra articulated connection) and figure 37 (a Class 13 truck with the extra articulated connection).

Figure 36. Photo. Class 10 truck, no second articulated connection.

Figure 37. Photo. Class 13 truck with a second articulated connection.