Patent Application
20210332541
The present disclosure is directed generally to a road safety system and more particularly to a vehicle escape ramp safety system that is designed to slow and stop an errant vehicle (e.g., truck) in a controlled, safe manner.
Vehicle escape ramp safety systems are designed to slow and stop errant vehicles in a controlled, safe manner during emergency situations. For example, the loss of braking capabilities on steep grades is a common situation where the vehicle escape ramps are used by errant vehicles.
There are several existing systems and methods that can be used to bring an errant vehicle to a safe stop. The CatchNet system, for example, employs net stations attached to energy absorbing steel tapes that can extend from housings that are fixed to opposing sidewalls (e.g., concreate barriers) that define an escape ramp and attach to a net. A single housing can include, for example, a 200 foot long coil of approximately 2 inch wide by 0.044 inch thick energy absorbing steel that is fed through a series of offset pins 217 arranged in the housing. At a net station, an equal number of housings (e.g., typically four or more housings) are attached to the left and right sidewalls by vertical pins/rods. The pins/rods allow the housings to rotate about a vertical axis and the tapes to follow with the net as an errant vehicle moves downstream about the ramp. Typically, there are a total of two, four, or six energy absorbing tapes per net station. On each side of the net, one tape is located near the top of the net and another tape is located near the bottom of the net.
Initially, each housing is positioned such that the housing pin, tape exit location and the net are all substantially aligned perpendicular to a sidewall of an escape ramp. When the net is impacted by an errant vehicle, it wraps around the front of the vehicle as the vehicle travels downstream along the ramp. Once the net becomes taut, the housings begin to rotate, and the tapes begin to extend out of the housing. As the tapes extend, the net applies a near constant force to the vehicle and thus begins the energy absorbing process to bring the errant vehicle to a controlled stop.
The near constant force applied to the vehicle via the net is controlled by the force required to extend the tape from each housing. This force is controlled by the frictional forces that occur between the tapes and the offset pins. In addition, this force is controlled by the forces involved with bending of the steel strap (e.g., tape) around the offset pins as it exits the housing. Thus, energy is absorbed by a combination of bending and friction forces.
The present invention is directed to an improved vehicle escape ramp arresting system. The present disclosure includes at least two improvements to the CatchNet System.
First, the internal width of the vehicle escape ramp is narrowed by reducing the interior width of the ramp (e.g., forming a tapered throat) just prior to net stations. The typical width of a vehicle escape ramp is 20 feet between the left and right longitudinal barriers and remains constant over the full length. The present invention includes a narrowed section that transitions from the typical 20 foot width to a reduced width of approximately 14 feet 6 inches immediately preceding each net station. The reduced sections located along the length of the vehicle escape ramp ensure that an errant vehicle remains centered as it traverses the ramp. In addition, the reduced sections aid to prevent the loading a net station eccentrically and in turn overloading one side of the net station's energy absorbers.
Second, the present invention includes a modified housing connection that serves two important functions: (1) it limits the peak initial load that can be applied to a tape during a vehicle impact with a net and (2) it allows the housing to rotate about both the vertical and horizontal axes. In an embodiment, a 200 foot long coil of steel strap weighing approximately 60 pounds is arranged in each housing. When a net station is impacted by an errant vehicle, the tapes are initially at rest (zero speed) and they must accelerate to the same speed as the errant vehicle in a short amount of time. At the onset of the impact, there is an increase in the pultrusion force due to the acceleration of the weight (e.g., 60 pounds) of the steel strap. Once the steel strap is pultruded at the same rate as the speed of the vehicle, this additional increase in the pultrusion force reduces to zero.
The modified connection reduces this initial peak force by extending the time over which the steel strap is accelerated to the speed of the vehicle. This is accomplished by using two steel straps that deform plastically at a load much lower than that required to pultrude the tape through the offset pins. The first steel strap begins to deform at approximately 25 percent of the pultrusion force of the tape. The second steel strap begins to deform at approximately 50 percent of the pultrusion force of the tape.
In addition, once the first steel strap has been deployed, the modified connection allows the housing to rotate about the horizontal and vertical axes. Prior to impact, the housing nests inside of the connection bracket such that it cannot rotate about the vertical plane and it remains in the horizontal plane. Once the net station is impacted the housing can immediately rotate about the vertical axis. Once the load applied to each energy absorber exceeds 25 percent of the pultrusion force, the housing is released to rotate about a horizontal pin through the connection bracket. This allows the tape to follow the net station in both the vertical and horizontal plane as the errant vehicle pushes it downstream. This reduces the possibility of the tape rubbing on the top or bottom of the housing as the net is pushed downward or upward by the errant truck and possibly causing the tape to rupture as it is deployed.
With reference now to the drawings and in particular
The overall length of the truck escape ramp can be, for example, at most 600 feet in length, and the narrowed sections or throats 204 and sidewalls 206 can be configured to be reinforced concreate that meet Test Level 5 (TL-5) criteria as defined by the AASHTO Roadside Design Guide.
The vehicle escape ramp system 200 is configured to be capable of slowing and stopping a vehicle (e.g., errant tractor-trailer) that can, for example, weigh up to about 90,000 pounds and be traveling upwards of about 90 miles per hour at initial impact of the net arresting system 200 with the net stations 209 configured to apply a maximum of 0.7 g. In an embodiment, the vehicle escape ramp system 200 can be configured to slow and stop an oversized vehicle (e.g., errant oversized tractor-trailer) that can, for example, weigh about 129,000 pounds and is traveling at about 90 miles per hour at an initial impact of the net arresting system 200 with the net stations 207 configured to apply a maximum of 1.0 g.
The purpose of the long and short absorber 234, 236 is to cushion the initial impact load applied to the housing assembly or canister 208 by an impacting vehicle 201, the modified connection reduces the initial peak force by extending the time over which the steel strap is accelerated to the speed of the vehicle. This is accomplished using two steel straps that deform plastically at a load much lower than that required to pultrude the tape 212 through the offset pins 217. The first steel strap 236 begins to deform at approximately 25 percent of the pultrusion force of the tape 212. The second steel strap 234 begins to deform at approximately 50 percent of the pultrusion force of the tape 212. The first steel strap 236 is the short U-shaped strap 236 and the second steel strap 234 is the long U-shaped strap 234. This is best seen in
In an embodiment, heating elements can be incorporated into the pavement of the ramp 202 to melt snow and ice.
Also, in an embodiment, the vehicle escape ramp 200 can be configured to bring an errant vehicle (e.g., pick-up truck) weighing about up to 4,400 pounds to a controlled, safe stop.
Although this invention has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. In addition, while several variations of the embodiments of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, including, but not limited to, the substitutions of equivalent features, materials, or parts, will be readily apparent to those of skill in the art based upon this disclosure without departing from the spirit and scope of the invention.
This application claims priority to U.S. Provisional Patent Application No. 63/014,854, filed on Apr. 24, 2020, the contents of which are incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63014854 | Apr 2020 | US |
