Taher Baghaee Moghaddam

Analysis of developed transition road safety barrier systems

Road safety barriers protect vehicles from roadside hazards by redirecting errant vehicles in a safe manner as well as providing high levels of safety during and after impact. This paper focused on transition safety barrier systems which were located at the point of attachment between a bridge and roadside barriers. The aim of this study was to provide an overview of the behavior of transition systems located at upstream bridge rail with different designs and performance levels. Design factors such as occupant risk and vehicle trajectory for different systems were collected and compared. To achieve this aim a comprehensive database was developed using previous studies. The comparison showed that Test 3-21, which is conducted by impacting a pickup truck with speed of 100 km/h and angle of 25° to transition system, was the most severe test. Occupant impact velocity and ridedown acceleration for heavy vehicles were lower than the amounts for passenger cars and pickup trucks, and in most cases higher occupant lateral impact ridedown acceleration was observed on vehicles subjected to higher levels of damage. The best transition system was selected to give optimum performance which reduced occupant risk factors using the similar crashes in accordance with Test 3-21.

The safety performance of guardrail systems: review and analysis of crash tests data

The last decade has witnessed an increased number of vehicles and increased vehicle speed on roads such that the frequency and severity of run-off roadway accidents has increased dramatically. Evaluation of guardrail system performance as an element of providing a safe environment for vehicles and to reduce occupant injuries is deemed to be vital issue. Hence, this paper is going to assess deflection and vehicle trajectory of current guardrail systems. For this purpose, the results of full-scale crash tests for different types of guardrail system are collected from previous crash tests available in the literature. The results showed that for Test 3–11 (according to NCHRP Report 350) with similar post spacing (1905 mm), the trend of vehicle exit speed declined while guardrail maximum permanent deflection increased. In addition, among all system types, guardrail with curb and Thrie-beam guardrail systems were subjected to the lowest amount of deflection although Thrie-beam guardrail was subjected to higher average values for both vehicle exit speed and exit angle. Further, weak-post guardrail system showed to have the highest maximum dynamic and permanent deformation compared to other systems whereas it caused the lowest exit angle to the vehicles.

The use of compressible packing model and modified asphalt binders in high-modulus asphalt mix design

High-modulus asphalt mix, Enrobé à Module Élevé (EME) in French, is a type of HMA representing high modulus or stiffness. Traditionally, EME mixes are fabricated with straight-run hard grade asphalt cement which has poor performance at lower temperatures and is very susceptible to low-temperature cracking in cold regions. The main objective of this study is therefore developing a new approach to EME mix design that contributes to good performance at high, medium and low temperatures. EME mixes have a dense structure. In this regard, Compressible Packing Model (CPM) was used to optimise the packing degree of EME mixes for two different mix types based on nominal maximum aggregate size (EME 12.5 and EME 19). In addition, three types of modified asphalt binders, namely: PG 88-28, PG 82-28 and PG 58-28 plus 10% Elastomer additives were used in this study. Thermo-mechanical tests were conducted to evaluate the performance of EME mixes in terms of stiffness, rutting, fatigue and low-temperature cracking. Obtained results showed that the developed mixes had acceptable performance at all levels, and that the mixes could satisfactorily perform at lower temperatures.