# Truck Axle Weights and Interaxle Spacings from Traffic Surveys in Mexican Highways
## 1 Introduction  
The weights and dimensions of heavy trucks are useful for engineering purposes. They can be used to investigate which gross vehicular weights (GVW) existent bridges are subjected to, or to compute the load effects that existent or future bridges should withstand; such load effects depend on a complex combination of axles weights and spacings, the position of the truck over the bridge, the bridge type, etc. They can also be used for extreme value projections of load effects, a reliability analysis of bridges under vehicular loads, and code calibration tasks.  
Recently, most of the information on traffic weights and dimensions has been collected through weigh-in-motion (WIM) recording systems [1, 2, 3, 4, 5]; broadly speaking, WIM data are recorded using sensors over the highway, whose signals are transformed into the requiredinformation with the aid of software (so it is not as direct as survey information). WIM systems have been also proposed for public roadways [6]. Another variant of WIM is bridge-WIM (BWIM), in which sensors are directly located in a bridge, either for vehicular or railway bridges [7; 8; 9; 10].  
The use of WIM data is very common, in contrast to traffic surveys. However, static surveys provide more direct information that can be used to calibrate the WIM information recorded on the same highway, since they are reliable and can be used as a benchmark [11]. These traffic surveys are challenging. Nevertheless, they could still be useful, as discussed in the present study. They may also be useful for other purposes, e.g., information on freight, driving practices, aging and other truck characteristics, dimensions, etc. This project report could be useful for planning and logistics considerations. Moreover, more than one source of information could be desirable for improving the assessment of bridge reliability, for instance combining WIM data with inventory information [12].  
Traffic surveys were conducted in Mexico for two highways in 2016 and another in 2018. They were part of a research project that included WIM recordings and were linked to another project for extracting concrete cores, all aimed at computing the reliability of vehicular bridges in Guanajuato (Central Mexico). Current research projects are still using this information to develop live load models for bridge design in Mexico and Mexico City. The traffic dataset can provide valuable information for engineers and possibly other experts in transportation and other fields.  
The main objective of the present study is to describe the surveys conducted during 2016 and 2018 in Mexico and to provide all the information to researchers and practitioners, including some statistics, a comparison of statistics versus WIM data, and discussions. It is also pointed out that this article is part of a larger ongoing project to compute the structural reliability of Mexican highway bridges, carry out code calibration tasks, and to propose live load models for bridge design in Mexico and Mexico City [13; 14; 15; 16].  
A description of the criteria to select the highways, surveying days, and time is provided. Equipment and logistics are also described. The results are reproduced in several tables from an open platform for data storage and publishing, where information can be retrieved through a DOI, referred to as \"associated DOI\" thereafter [17]. These tables are described; some basic statistics are computed and compared with WIM data and with nominal trucks used by designers and discussions are included.