# Truck Axle Weights and Interaxle Spacings from Traffic Surveys in Mexican Highways
## 4 Data and Some Statistics, Comparisons and Discussion
### Discussion for the Surveys in 2016  
In Table 1 the vehicles surveyed, in terms of GVW and axle weights, are listed. The first and last columns in Table 1 correspond to the truck designation and the GVW, respectively, while the columns in the middle correspond, from left to right, to the axle weights from  
Figure 4: C3 truck loaded with construction material. Pictures are either by the authors and/or by the IMT reports hired by UG [22,23]. Figure 5: Nominal (**a**) T3S3 and, (**b**) T3S2R4 trucks that have been used by designers in Mexico. front to rear in increasing order, respectively. To exhaustively compare data in Table 1 versus WIM data is out of the scope of the present article, some broad comparisons can be mentioned though. For instance, if the 5-axle vehicles in Table 1 are considered (10 samples for T3S2), an average GVW of 220.47 kN and a sample standard deviation of 80.36 kN are obtained. Although the sample is very small, it is consistent with WIM data for the same highway recorded in 2009 and 2017, leading to sample sizes of 322,680 and 11,782 vehicles, respectively, an average of GVW of 178.36 kN and 362.09 kN, respectively, and standard deviation of GVW of 94.86 kN and 63.17 kN, respectively [16]. The smaller average value and larger variability for the 2009 WIM data could be attributed to a much longer (continuous even at nighttime) recording period, including possible seasonal effects and many more unloaded vehicles, while for the 2017 WIM data, recording heavier vehicles was deliberately pursued [21]. The fact that the much smaller sample of this study, but through direct static measurements on field, is within the limits of the WIM databases, could support and give confidence in the use of the WIM data for code calibration tasks, law enforcement, or other aspects. It is noted that for this truck designation (T3-S2 in Table 1), no truck was over the legal allowed weight of 456 kN for this considered highway [24]. This is expected, since the police help was not obtained and truck drivers were directly asked to be measured, as stated before. The previous discussion indicates that the traffic surveys are consistent with WIM data and can be useful, but also that a formal statistical comparison would deserve future research, since the available information corresponds to samples of different sizes and types, different recording periods under different recording strategies, and is affected by different vicissitudes. For instance, for the 2016 surveys, length and interaxle distances were not measured, but the IMT provided typical distances for recorded vehicles based on their databases. These are listed in Table 2 for the truck designation in the first column; the distances are presented in a cumulative manner, i.e., the second column lists the distance between the first and the second axes, the third column lists the distance between the first and the third axes (not between the second and the third) and so on. For example, if the typical interaxle distance for the last tandem in a truck designation T3S2R4 is of interest, the distance \"1 to 8\" in Table 2 can be subtracted from the distance \"1 to 9\" to get 1.21 m. It is indicated that a variation between approximately 10 to 20 cm could be expected for the trucks in Table 1 and others in this study [22]. It could also be of interest to compare the distances in Table 2 and others reported later (actual measured ones) with some nominal models that have been used by bridge designers in Mexico, as those shown in Figure 5[16], which correspond also to two of the designations in Tables 1 and 2. Note that such differences could have implications in bridge design and code calibration, whether they are obtained through WIM data or, more precisely, through direct measurements in the field, as are those reported later in the present study. Tables 3 and 4 list also GVWs and axles weights from the 2016 surveys, but in this case for the two-lane highway and both directions, respectively.