# Truck Axle Weights and Interaxle Spacings from Traffic Surveys in Mexican Highways
## 4 Data and Some Statistics, Comparisons and Discussion
### Discussion for the Survey in 2018  
In Tables 5 and 6 the vehicles surveyed in 2018 are listed in terms of weights and interaxle distances for the same trucks, respectively. Unlike Table 2, in Table 6 the actual interaxle distances measured in the field are reported; the format is also different, because in Table 6 the interaxle distances are directly given, i.e., \"1 to 2\" denotes the column with interaxle spacing between axle 1 and 2, \"2 to 3\" between axle 2 and 3, etc. This survey was only carried out for the Irapuato-Zapotlanejo highway and, since experience was gained in the 2016 survey (it is larger in the number of recorded trucks), it is focused only on trucks, and on obtaining heavy GVWs by inspecting WIM data [21], and the help of the Federal Police. In Tables 5 and 6, it can be seen that differences do exist in relation to the nominal trucks in Figure 5, which have been used for bridge design, as stated earlier. Some axle weights in Table 5 are even larger compared to the nominal trucks in Figure 5, information that we consider relevant for the readers of this Project Report. It is once more pointed out that a rigorous statistical analysis and comparison versus WIM data is not pursued because a one-to-one correlation is not possible, and because the characteristics, decisions, and vicissitudes of each set of traffic data are very different, and an adequate statistical comparison would be challenging, though it could be approached in future studies. Nevertheless, some broad comparisons and conclusions can be drawn. With this purpose, we focused on the trucks designated as T3S2R4 (except the one with the uplifted axles). If the average interaxle distances in Table 6 for the 19 T3S2R4 trucks are computed (front to rear), values of 4.64 m, 1.33 m, 6.94 m, 1.26 m, 2.60 m, 1.29 m, 6.47 m and 1.27 m are obtained. These are larger distances as compared to those in Figure 5b, except by the interaxle distance between axle 5 and axle 6 (3.2 m), which is 0.6 m smaller on average. Additionally, the average and the standard deviation is also computed for the 19 T3S2R4 vehicles in Table 5, for the GVW and for the heaviest axle from each truck. This resulted in 488.01 kN and 213.11 kN for the average and sample standard deviation of GVW, respectively, and in 73.42 kN and 24.57 kN for the average and sample standard deviation of the heaviest axle, respectively. If compared, for instance, with the corresponding values from the WIM data for the same highway recorded in 2009 for 9-axle vehicles (a sample size of 71,303 vehicles) [16], that resulted in average and standard deviations for GVWs of 321.13 kN and 184.16 kN, respectively, it can be concluded that the values are consistent in average and variability; the larger average for the surveys could be explainedbecause it was purposedly intended to record heavy trucks [21]. Regarding the statistics for the heaviest axles, the WIM data from 2009 led to average and standard deviation values of 47.61 kN and 26 kN, respectively, which are roughly consistent with those reported in this study, and similar conclusions could be drawn. Although the comparisons are in general consistent, it should be noted that in [16] not necessarily all 9-axle trucks are T3S2R4 (for instance), although it is the only legal configuration with 9 axles as per [24]. Further research is recommended for a more detailed analysis. The above basic statistical analysis and comparisons are not exhaustive, but they highlight the importance of the data. Other aspects can be highlighted once more. If, for instance, Tables 5 and 6 and the trucks designated as C3 are inspected, it can be noticed that the tandem interaxle distance is approximately 1.3 m on average and the axle weights can each be approximately over 130 kN, which is heavier than the design tandem used by AASHTO [26] and previous versions. Also, Table 5 shows that several trucks designated as T3S2R4 have GVWs well over 652.37 kN (the lower limit for the maximum legally allowed GVW depending on the truck conditions [24]).