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In order to evaluate the variation in distance estimation accuracy, a survey was conducted during which 123 subjects estimated distances to static objects in a roadway setting. The subjects (which included many police officers) tended to underestimate distances to objects that were from 21 to 383 feet away; the average estimation error was −8.6% while the median error was − 22%. The variation in performance among individuals was extremely large, with extreme errors ranging from − 96% to + 811%. The distribution of error did not conform to a Gaussian (normal) distribution because of the skew of the observed error distribution towards large positive errors. Box plots were used to identify nine “outlier” respondents who produced a total of 15 error estimates which were extraordinary in their difference from the rest of the data.

This paper investigates the coefficients of static and kinetic friction between the hardwood flooring of a used van-type semi-trailer and the bottom surfaces of pallets fabricated from: high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), oak, or hickory. Tests to determine static and kinetic coefficients of friction (COF) were performed with the pallets moving longitudinally or transversely across the cargo trailer floor, and with varying loads. Using a general linear model to analyze the data collected, the best estimates of the COF (static, kinetic) for each pallet were found to be: HDPE (0.31, 0.20), LLDPE (0.29, 0.24), hickory (0.32, 0.21), oak (0.35, 0.25). The analysis also showed that pallet load had a small but statistically significant effect on the friction coefficients.

This paper investigates the coefficients of static and kinetic friction between the hardwood flooring of a used semi-trailer and the bottom surfaces of both an old and a new hardwood pallet, with varying cargo weights, at varying locations in the trailer. A total of 22 tests were performed with the pallets moving parallel to the longitudinal axis of the trailer and perpendicular to this axis. The results show that the variations in load did not statistically affect the friction coefficients. The older pallet had statistically smaller static and kinetic friction coefficients (s=0.32, k=0.26) than that of the newer pallet (s=0.35, k=0.29). The static friction coefficients were statistically dependent upon whether the test took place at the front (0.36), middle (0.34) or rear (0.32) of the semi-trailer. Kinetic coefficients behaved similarly: front (0.29), middle (0.27) or rear (0.26).