# Comparative Accuracy Analysis of Truck Weight Measurement Techniques
## 4 Discussion
Since the \(t\)-test concluded that the measurements are statistically different, it is crucial to account for the allowable tolerances specified by ASTM 1318E-09 WIM Type I. The traffic weight measurement tolerances established by ASTM WIM Type I indicated \(\pm\)10% tolerance for GVW measurements, \(\pm\)20% for individual axle weight, and \(\pm\)15% for a group of axles. The tolerances needed to be within 95% of the respective data items recorded by the WIM system. The analysis was conducted for portable scales, where those certified scales were compared to weigh station, WIM, and B-WIM measurements. Figure 10 shows the results of the analysis of available measured vehicle attributes. For B-WIM measurements, almost all measured attributes are with the tolerance requirements. Only the 5 th axle weight and second tandem axle (axle 4 + 5) provide the results at 90% tolerance, which is very close to the desired safety level. For the truck weigh station, the 1 st axle weight measurements indicated 100% of the tolerance level measurements. But GVW and second tandem axle weight was below the required 95% compliance, and the tolerance was at 84-86%. Most of the measured vehicle attributes fulfilled the WIM measurements' requirements, but in the case of GVW, the 4 th axle weight and second tandem axle provided a tolerance that varied between 87-92%. It was in very close proximity to the anticipated safety level. For all three weighing systems compared to the certified portable scales, it could be noticed that the last two axles, and therefore the second tandem axle, provided the lowest tolerance level. The tolerance check was conducted for the truck weigh station, which captured: GVW, 1 st axle weight, and two tandems. Those vehicle attributes were compared to B-WIM, portable scales, and WIM measurements. Figure 11 presents a summary of the tolerance analysis. B-WIM's tolerance level varied from 88-97%, which was close to the required safety. For portable scale measurements, the tolerance varied between 92-99%, which gave good results while comparing static weight measurements. The WIM data tolerances were between 84-96%, where the GVW and two tandems were below the required safety level. Also, in comparison to the tolerances with truck weigh station, it was noticed that the second tandem axle measurements provided the lowest tolerance to meet the 95% compliance. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multirow{2}{*}{
\begin{tabular}{c} **Mean and SD** \\ **of Difference** \\ \end{tabular} } & \multicolumn{3}{c}{**Portable Scales**} & \multicolumn{3}{c}{**Weigh Station**} \\ \cline{3-8}  & & **B-WIM** & **Weigh Station** & **WIM** & **B-WIM** & **Portable Scales** & **WIM** \\ \hline GVW & Mean & 2.25 & 1.56 & 3.27 & 2.74 & 1.56 & 3.24 \\  & SD & 2.42 & 2.48 & 2.76 & 3.18 & 2.48 & 3.36 \\ \hline \multirow{2}{*}{W1} & Mean & 2.03 & 0.89 & 1.55 & 1.63 & 0.89 & 1.11 \\  & SD & 3.74 & 2.55 & 3.16 & 3.27 & 2.55 & 2.13 \\ \hline \multirow{2}{*}{W2} & Mean & 2.85 & - & 1.85 & - & - & - \\  & SD & 5.28 & - & 4.08 & - & - & - \\ \hline \multirow{2}{*}{W3} & Mean & 2.76 & - & 1.80 & - & - & - \\  & SD & 5.14 & - & 3.68 & - & - & - \\ \hline \multirow{2}{*}{W4} & Mean & 2.95 & - & 2.54 & - & - & - \\  & SD & 5.20 & - & 4.20 & - & - & - \\ \hline \multirow{2}{*}{W5} & Mean & 2.93 & - & 2.38 & - & - & - \\  & SD & 4.97 & - & 4.05 & - & - & - \\ \hline \multirow{2}{*}{AG1} & Mean & 1.25 & 1.24 & 1.52 & 1.75 & 1.24 & 1.99 \\  & SD & 1.32 & 2.50 & 2.26 & 2.59 & 2.50 & 2.99 \\ \hline \multirow{2}{*}{AG2} & Mean & 1.66 & 1.44 & 2.11 & 2.46 & 1.44 & 3.03 \\  & SD & 2.33 & 2.94 & 2.05 & 3.11 & 2.94 & 3.47 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Mean and standard deviation of difference for vehicle attributes compared to portable scales and weigh station measurements. Correlation coefficients were calculated for the portable scales data set and three other data weighing systems.