# Truck Axle Weights and Interaxle Spacings from Traffic Surveys in Mexican Highways
## 3 Logistics, Equipment, and Survey Procedure
### Survey in 2018  
The third survey took place on 23 February 2018, from 5 a.m. to 1 p.m. (local time), once more on the Irapuato-Zapotlanejo highway in the same place; it was decided to carry out the survey again at this site and in the same direction because very heavy trucks circulate on it, according to WIM data, as well as to facilitate logistics. The equipment used was the same, except that the calibration certificate number was IC-IP-073/17, issued on 28 August 2017 [23]. This time, help from the Federal Police was successfully obtained, \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Truck Designation** & **Axle 1** & **Axle 2** & **Axle 3** & **Axle 4** & **Axle 5** & **GVW** \\ \hline C2 & 16.38 & 15.98 & - & - & - & 32.36 \\ C2 & 26.58 & 29.62 & - & - & - & 56.19 \\ C2 & 26.38 & 32.75 & - & - & - & 59.13 \\ C2 & 25.11 & 46.29 & - & - & - & 71.39 \\ C2 & 36.77 & 47.56 & - & - & - & 84.34 \\ C2 & 40.40 & 46.09 & - & - & - & 86.49 \\ C2 & 41.38 & 53.35 & - & - & - & 94.73 \\ C2 & 42.56 & 56.88 & - & - & - & 99.44 \\ C3 & 35.40 & 26.09 & 29.91 & - & - & 91.40 \\ T3S2 & 41.38 & 39.62 & 39.13 & 31.09 & 45.21 & 196.43 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Weights [kN] obtained at Guanajuato-Los Infantes highway in 2016 (direction to Los Infantes). \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Truck** & & & & & \\
**Designation** & **Axle 1** & **Axle 2** & **Axle 3** & **Axle 4** & **Axle 5** & **GVW** \\ \hline C2 & 33.54 & 84.24 & - & - & - & 117.78 \\ C2 & 41.38 & 76.69 & - & - &  
One important aspect that is observed in the values in Table 5 is that many trucks are well over the legal weight in Mexico [24] for GVWs. The maximum allowed GVW for Mexico depends on the type of highway and truck configuration and its physical conditions; however, it normally should not exceed approximately 650 kN [24]. This aspect is important, since it proves that the overweight reported in WIM data is not due to calibration or recording problems, but that non-legal weights are actually circulating on Mexican highways; some of the GVWs in Table 5 are well over the legal weight mentioned above. This it to be disused in more detail in Section 4. It demonstrates the importance of static surveys as a support for WIM data. It is noteworthy to mention that overloads are critical not only for bridges but also for the pavement's lifespan [25]. The information contained in this study could also be useful for pavement researchers. In addition, it was noticed in the field that several 3-axle trucks, denoted as C3 in the tables given later in this study (see also Table A1 in Appendix A and the associated DOI [17], where all truck designations used in this study are listed and depicted), were loaded with construction material (e.g., sand), well over the trucks' own height, and were deemed overloaded by simply looking (e.g., Figure 4). This was confirmed when the final report was submitted, as will be observed in Table 5 later, where several C3 trucks with GVWs of approximately 350 kN are listed; the maximum allowed GVW for this truck and highway should not be normally over approximately 270 kN [24]. Moreover, from Tables 5 and 6 listed in the next section (Section 4), it can also be noticed that the surveyed C3 trucks represent approximately a tandem load (the last two axles) of two 140 kN axle loads separated by an axle spacing of 1.3 m; which can be compared with that for bridge design in the AASHTO standards (e.g., [26] and previous versions), which is defined by two 111 kN loads with a 1.2 m spacing. Trucks with less than six axles (such as C3 trucks and others) could generate load effects on short-span bridges (e.g., 6-10 m spans) that are larger than those generated by 6- to 9-axle vehicles (whose GVWs are much larger) normally considered by bridge engineers for design [8,9] (see also Figure 5 in Section 4). This information is deemed relevant for the structural engineering field, and the data reported in this study can be used as a reference for these cases.