Motorways are usually perceived as the safest part of the road infrastructure. Nevertheless, the junctions and exit ramps on them can still present a safety challenge due to high average velocities ...and obstacles installed to contain the out-of-control vehicles within the roadway. Recently, the gravel arrester-beds have been constructed on many locations on motorway junctions and exit ramps. They present a viable alternative to the rigid barriers and deformable crash-cushions normally used on these locations. They help decelerate the vehicles by dissipating the kinetic energy in the gravel bed and thus stop the vehicles more gradually on a longer distance, causing lower average decelerations and thus reducing passenger injuries. Furthermore, by proper design, they can reduce the damage sustained by the vehicles and the infrastructure and thus shorten the times required to re-open roads after incidents. The paper provides an insight into the subject and presents some recent findings obtained from measurements on a test site, and from simulations with different types of vehicles. The parameters and their required values for optimizing the efficiency of gravel arrester beds for different requirements are discussed in the final part.
This study employs the discrete element method to investigate the influence of particle size on the load-bearing characteristics of aggregates, with a specific emphasis on the aggregates used in ...escape ramp arrester beds. This study utilises the log edge detection algorithm to introduce an innovative approach for modelling irregularly shaped pebbles, integrating their physical properties into a comprehensive discrete element model to enhance the accuracy and applicability of simulations involving such pebbles. Meticulous validation and parameter calibration (friction coefficient: 0.37, maximum RMSE: 3.43) confirm the accuracy of the simulations and facilitate an in-depth examination of the mechanical interactions between aggregate particles at macroscopic and microscopic scales. The findings reveal a significant relationship between the particle size and load-bearing capacity of aggregates. Smaller pebbles, which are more flexible under pressure, can be packed more densely, thereby improving the distribution of vertical forces and increasing the concentration of local stress. This enhancement substantially increases the overall load-bearing capacity of aggregates. These discoveries hold significant implications for engineering practices, particularly in the optimisation of safety for truck escape ramps and in identifying the ideal sizes of pebbles with irregular shapes.
At motorway junctions, crash cushions are usually installed to stop impacting vehicles safely. Gravel-filled arrester beds can be used as replacements for crash cushions. They offer improved safety ...by effectively using an already available large area, and lower-severity impact parameters for passengers while safely stopping the vehicle. The work presented in this paper was conducted to investigate the behaviour of passenger cars on gravel-filled arrester beds. For that purpose, a gravel-filled arrester bed was built, and a series of experiments was performed with passenger cars entering the arrester bed at an initial velocity of up to 75 km/h. Numerical analyses were also performed to validate the model as well as to examine the response of larger vehicles under a variety of conditions. The results have shown that gravel arrester beds can be used to stop heavier errant vehicles safely near road junctions.
Gravel-filled arrester beds, also called safety-escape ramps or vehicle run-out areas, have long been a road-safety feature for safely stopping heavy road vehicles from running off the road. In the ...recent past, there has been consideration given to installing these features on highway access ramps to provide safe areas to stop passenger cars driving at highway speeds. The work presented in this article was performed to investigate the behaviour of standard-size passenger cars on gravel-filled arrester beds, with a particular focus on the achievable vehicle decelerations and the ability of the arrester beds to safely stop a passenger car coasting in an uncontrolled manner. The findings show that the achievable average decelerations are in the range of 0.3 g for coasting vehicles and up to 0.9 g when the vehicles are braking. The results prove that more research is required to quantify the influence of the gravel parameters on the achievable decelerations.
The design and the construction of currently employed aircraft arrestor beds require the presence of soft ground in which an aircraft in overrun decelerates as a result of drag forces acting on its ...landing gear. During this interaction, the wheels crush or displace the material until the airplane is completely stopped. The arresting systems are of special importance for those airports that do not have a safety area of the length required by international regulations. In the recent past, several materials with the capability for high energy absorption have been proposed, but most of them have been rejected so that some secondary effects—such as dust production during overrun, which leads to engine failure; short durability to environmental conditions; and limited mobility for rescue vehicles—can be reduced. This paper describes an experimental investigation performed on new materials by employing innovative testing protocols. Four materials of low density and low compressive strength—such as cellular mortar, cellular mortar with expanded polystyrene, and expanded clay pellets with bitumen and cement binder—have been considered. Quasi-static tests have been performed to define elastic–plastic transition points, and impact tests have been considered to assess the amount of energy that can be absorbed under the gears during the collapsing phase. Performance indicators of these new materials have been highlighted and compared with traditional indexes normally used for the characterization of existing arrestor beds.
In most aircraft overruns, an aircraft comes to a stop within 1,000 ft (305 m) of the runway threshold. In response, U.S. airfields are required by FAA to have a 1,000-ft runway safety area in ...addition to the design runway length in case of aircraft overruns. At airfields where space is limited, airport operators need to consider alternative solutions. One solution is for an airport operator to reduce runway length and therefore limit aircraft types landing at their airport. Conversely a more attractive solution is for an airport to implement an engineered material arrestor system (EMAS). An EMAS is a passive system comprising a cementitious type material. Aircraft deceleration occurs because of drag forces that are incurred by the aircraft landing gear as the aircraft passes through and crushes the arrestor material. Parameters significantly influencing a B727 or B747 aircraft's stopping distance as it traverses an EMAS are presented. The computer code, ARRESTOR, developed for FAA, was used to compute the aircraft stopping distances. Five aircraft parameters (mass moment of inertia, weight, wheel friction, reverse thrust, and center of gravity location) for each aircraft type are examined, along with two arrestor material types (low-density concrete and phenolic foam) and three arrestor bed geometries. Each parameter is individually varied to investigate stopping distance sensitivity. Twenty-one overrun simulations were used in the aircraft parameter study, and 100 overrun simulations were used to determine an optimal material compressive strength. Arrestor bed geometry was investigated by using 32 overrun simulations. Study results are summarized in plots and tables.
The load-bearing capacity of pebble aggregates plays a pivotal role in influencing the operational performance of uncontrolled trucks on arrester beds. The complexity of this phenomenon stems from ...the nonuniformity in the shapes of the pebbles and their stochastic arrangement within the beds, presenting notable challenges for traditional mathematical modelling techniques in precisely evaluating the contact dynamics of these aggregates. This study leverages the discrete element method (DEM) to extensively analyse the arrester bed aggregate of a standard truck escape ramp. The aforementioned mechanism entails the gathering of morphological parameters of irregularly shaped aggregate particles and introduces a novel method for constructing random shapes that adhere to the observed distribution characteristics. A discrete element model, grounded in the physical properties of these aggregates, is formulated. This study focuses on the aggregate’s load-bearing capabilities, scrutinising the mechanical behaviour of the aggregate particles at the macroscopic and microscopic scales. These insights offer substantial scientific contributions and practical implications for assessing the safety of escape ramps and determining essential parameters for the brake bed design.
This paper presented a numerical analysis of the damping characteristics of truck escape ramps. To explore the procedure of out-of-control trucks running into arrester beds, the discrete element ...method (DEM) models of both the tire and the truck escape ramp were built. Tire compression tests were conducted on a homemade tire test system, and the results were used to calibrate the parameters of the tire DEM model. A compression machine was used to conduct dynamic compression tests on pebbles obtained from escape ramps, and the results were used to calibrate the parameters of the pebble DEM model. Road tests were then conducted to further validate the simulation method. An adaptive master-slave simulation procedure analysis was utilized in the simulation process. The error of the travel distance between the simulation and test results was 2.95%. The built tire-pebble DEM model was used to perform the simulations of trucks running into truck escape ramps with different truckloads and laying depths. The results of different truckloads indicated that the truck speed was mainly determined by the laying depth at the entrance of the truck escape ramp. With an increase in time, the truckload started to take effect. The results of different laying depths indicated that the truck speed results were approximately constant at the entrance of the truck escape ramp. As the laying depth increased, the truck speed decreased. When the laying depth exceeded approximately 60 cm, the damping properties of the different laying depths were approximately constant.
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