This study aims at exploring the influence of different modifiers on the physical and rheological properties of asphalt cements. Crumb Tire Rubber (CTR), Microcrystalline Synthetic Wax (MSW), and Nano Silica (NS) modifiers were used to modify asphalt cement of 60/70 penetration grade. Several percentages of CTR (9, 12, and 16%), MSW (2, 3.5, and 5%), and NS (3, 5, and 7%) by weight of the asphalt cement were tested. The penetration, softening point, flash and fire points, viscosity, dynamic shear rheometer (DSR), and bending beam rheometer (BBR) were carried out in this study. Experimental results showed an improvement in the high-temperature performance of asphalt cement by adding CTR and NS modifiers while adversely affecting properties at low temperatures. Also, the results did not show any enhancement in the high or low-temperature performance by adding MSW to the asphalt cement. The optimum contents of CTR and NS modifiers were found to be 12% and 5% by weight of the asphalt cement, respectively.

The objective of this study was to identify the most salient driver faults that cause crashes on some Jordanian rural and suburban roadway segments, to examine crashes with distracted driving as the driver’s fault, and to investigate the differences between crashes caused by distracted driving. Data for more than 10,200 crashes on nine roadway segments (five rural and four suburban) were accessed from the relevant government agency, but only n = 2472 were used for analysis after controlling for crashes specified as being caused by drivers’ distracted driving. IBM SPSS version 22 was used to perform descriptive analysis and independent samples’ t-tests. The results revealed that distracted driving was the second most common driver fault to cause crashes and the second main cause of fatalities and injuries on both rural and suburban roadways. Distracted driving on rural highways appears to be more fatal, whereas it caused more crashes with severe injuries on suburban roads. The variables at junction, road grade, number of lanes, weather condition, crash type, and number of vehicles involved were found to be statistically significant but with a small effect size. The following categories showed high percentages of distracted driving crashes on rural and suburban roadways: males, drivers 25–39 years old, non-holidays, weekdays, tangent sections, two-way divided roads, not at junction, level roads, two-lane roads, clear weather, dry surface, daylight, and automobile vehicles showed high percentages of distracted driving crashes on rural and suburban roadways. Differences between crashes on rural and suburban roadways caused by distracted driving were found to be small.

This research investigates the effect of adding three different modifiers to laboratory-prepared Superpave asphalt concrete mixtures to evaluate their ability to strengthen and reinforce asphalt concrete mixtures and improve their rutting resistance. The three used modifiers were Crumb Tire Rubber (CTR), Microcrystalline Synthetic Wax (MSW), and Nano Silica (NS). The CTR, MSW, and NS modifiers were added at their optimum contents determined previously which were 12%, 2%, and 5% by weight of asphalt binder, respectively. Asphalt concrete mixtures were tested at two temperature levels; 40°C and 55°C, and were compacted at two compactive efforts to simulate high and low levels of traffic with N_des= 119 and 82, respectively. Static creep test was used to evaluate the effect of changing modifier type, temperature, and compactive effort on creep properties and rutting potential of modified mixtures through studying five creep parameters. These parameters were accumulated axial micro-strain, creep stiffness, steady state creep slope, creep compliance, and creep compliance parameters. Results revealed that all the used modifiers had improved mixture performance. It was found that CTR modified mixtures had the best performance at high temperature level, while NS modified mixtures showed the best performance at medium temperatures. Moreover, it was found that lower temperatures and higher compactive efforts increase mixture stiffness and decrease deformation and their rutting potential. Statistical analysis was carried out and regression models were developed for the prediction of stiffness modulus, accumulated axial micro-strain, and steady state creep slope as a function of modifier type (MT), testing temperature (Temp) and compactive effort (CE). Models yielded relatively high coefficients of determination (R²) and adjusted R², indicating their ability in explaining much of the variability in the response variables.