USRE29544E - Energy absorbing deceleration barriers - Google Patents

RELATED APPLICATION

This application is a continuation-in-part of application Ser. No. 665,359, filed Sept. 5, 1967, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to highway safety devices and more particularly to such devices for decelerating uncontrolled or improperly controlled vehicles as they approach immovable obstructions such as bridge abutments or as they leave the highway at a point of particular danger.

As is well known, the matter of reducing the highway fatality and injury rate has been the subject of increasing attention in recent years. The matter of highway safety includes a number of factors such as the quality of the vehicle, the training, skill and experience of the driver, the highway system itself and the establishment and enforcement of intelligent safety laws. Limited progress is being made in all of these areas.

Studies have demonstrated that more than a third of fatal accidents involve only one vehicle. In the usual case the driver loses control of the vehicle which then leaves the road and often strikes a fixed obstruction unavoidably in position adjacent to the highway and which may be a part of the highway system itself such as a bridge abutment. In such a case the occupants of the vehicle can be protected only by controlling the rate of vehicle deceleration to reduce the risk of injury caused by the "second collision" which occurs when the occupants strike the interior of the vehicle.

Since the impact velocity of the vehicle is beyond control and its final velocity is zero, the risk of injury can be reduced only by increasing the distance through which the vehicle and is occupants are decelerated.

Accordingly, it has been proposed to introduce sacrificial energy absorbing devices in the path of the vehicle adjacent to heavy fixed obstructions. Despite the need for such devices and their obvious advantages, insofar as presently known none have been accepted in any significant number either because of lack of efficiency, prohibitive cost or because in some cases they increase the hazard or become hazardous themselves. Examples of such prior proposals may be found in U.S. Pats. 2,088,087; 2,375,443; 3,141,655; 3,288,440, and 3,292,909.

Among the deficiencies of most, if not all, of these prior proposals in their tendency to substitute one uncontrolled motion for another, i.e., to deflect the vehicle into the path of an oncoming vehicle; to improse an overturning moment on the vehicle, to create a secondary hazard, i.e., where the energy absorbing devices themselves may be projected into the path of outer vehicles, or to subject the vehicle and its occupants to severe deceleration forces.

The familiar guard rails of various types, median dividers, fences, and walls are "tangent deflection" devices intended to deflect any vehicle which strikes them tangentially. For the most part they are intended simply to change the direction of the vehicle without appreciably reducing its velocity or momentum. Since the tangent deflection devices are usually anchored and usually have greater rigidity than vehicles, they constitute in themselves further obstructions along the highway, especially when the ends of "tangent deflection" barriers are exposed to vehicle impingement. Then when they are struck by a vehicle travelling in a path at right angles or at a high angle to the barrier, the results are often as severe as when a vehicle strikes a bridge abutment or other fixed obstruction. This is because the "tangent deflection" barrier is, in these cases, being misused to perform the function of a "head-on" type of barrier. Most, if not all, of the prior barriers are by design intended to arrest or deflect the movement of the vehicle within a fixed, usually very short, distance regardless of the speed and weight of the vehicle. The result generally is the imposition of catastrophically high forces on the vehicle and the occupants.

SUMMARY OF THE INVENTION

With the foregoing considerations in mind, it is the principal purpose and object of the present invention to provide improved devices for decelerating vehicles which obviate the above-stated disadvantages of prior proposals and which provide for controlled deceleration of vehicles without the creation of the secondary hazards noted above.

It is a further object of the present invention to provide an array of barrier units of novel construction adapted to be positioned to intercept a vehicle moving toward an immovable object to progressively decelerate a vehicle by displacement or dispersion of all or a portion of the mass represented by the units.

It is a further object of the present invention to provide improved deceleration barriers which are effective to decelerate a vehicle at a controlled rate while imparting a horizontal or overturning-resisting force on the vehicle at whatever angle or attitude the vehicle strikes the barrier.

It is an additional object of the present invention to provide improved deceleration barriers for vehicles which are effective to "catch" the vehicle without substantial deflection of the vehicle while simultaneously eliminating the so-called ramp or lifting effects.

It is also an object of the present invention to provide improved deceleration barriers which are of relatively uncomplicated mechanical construction and which can be manufactured and sold and erected at a cost which permits their use as sacrificial units.

In attaining these and other objects, the present invention provides an array of sacrificial arrier units comprising weights spaced and arranged to suit the requirements of a particular installation. Preferably, the individual weights are light, breakable containers the upper portion of which contains a dispersible mass such as sand or water and the lower portion of which is of light-weight crushable construction to prevent a ramp effect which would project the vehicle upwards or give it an overturning vertical acceleration. Thus, the center of gravity of the individual weights is preferably at least as high as that of the average vehicle (about 22 inches) which permits the weights to impart a horizontal or overturning-resisting force on the vehicle at whatever attitude or angle the vehicle strikes the weight. Each weight may be connected to the other weights by a cable system with the cables being so arranged as to "catch" the vehicle in such a manner to prevent the vehicle from proceeding over or nosing under the cable and to prevent injury to the occupants of the vehicle by the cables.

The individual weights preferably comprise sand filled frangible plastic containers which are of relatively inexpensive, knockdown construction. The containers may be easily transported to the site, erected, filled with a dispersible mass and covered or sealed. Since they are not anchored and require little or no site preparation, their installation or replacement may be accomplished at minimum cost.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic top plan view of the barrier in accordance with the present invention shown in its normal initially installed configuration;

FIGS. 2 and 3 are side elevations taken 90° apart of one form of the individual barrier units;

FIG. 7 is a perspective view illustrating the components of a knockdown container;

FIG. 8 is an exploded view of the container of FIG. 7 shown partially erected;

FIG. 9 is a perspective view of the container components of FIGS. 7 and 8 shown erected and installed;

FIG. 11 is a vertical section illustrating a slightly modified container;

FIG. 12 is an exploded view showing the components of another form of container;

FIG. 13 is a perspective view showing the components of FIG. 12 assembled and installed;

FIG. 14 illustrates a further modification of one of the individual units;

FIG. 15 illustrates graphically a specific array of units and performance data;

FIG. 16 is a diagrammatic top plan view of another embodiment of the barrier in its normal initially installed configuration;

FIG. 17 is a view similar to FIG. 16 but illustrating the configuration of the barrier system after it has been struck by a vehicle;

FIG. 18 is an enlarged view showing a pair of interconnected units incorporated in the barrier system of FIGS. 16 and 17; and

FIG. 19 is a view similar to FIG. 16 but showing a modified application of the barrier system of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

The individual units may take a variety of forms. In general they comprise a light, breakable container filled with a dispersible mass such as sand and are so constructed as to dispose their center of gravity at least at the level of the center of gravity of the vehicle. Preferably the units are of cylindrical form, this form being preferred to simplify manufacture and assure low cost and to minimize damage to the vehicle upon impact. Typically, they are from 20 to 40" in diameter and 24 to 36" high to perform their dynamic function in a practical form. A presently preferred form of the individual units is shown in FIGS. 2-6 to which detailed reference will now be made.

At the time of installation of the barrier system, a supply of container bodies, lids and cores and a supply of sand is trucked to the desired site. The container bodies are then arranged in the desired pattern. Since they are of light-weight construction they may be set in place manually without difficulty. Little or no site preparation is required since the units are not anchored to the ground and since they impose a load on the supporting surface of not more than approximately 2 lbs. per square inch the available surface is adequate for support. After the container bodies are suitably arranged, the cores are slipped in place, the space above the cores is filled to the desired level with sand and the lids are snapped in place. The number, size and disposition of the weights depends on the anticipated speeds and weight for the vehicles travelling along the adjacent highway and are thus subject to some variations. A typical array of weights shown diagrammatically in FIG. 1 and graphically in FIG. 15 is intended for installation in front of a fixed abutment adjacent a highway along which passenger cars are expected to travel at the usual highway speeds.

The barrier system of the present invention comprises a number of individual units rather than a single unit for several reasons. A relatively minor consideration is the ease of manufacturing, shipping and handling the smaller units.

Of much greater importance is the flexibility permitted in arranging the units and particularly to impart to the barrier system the capability of functioning as a variable capacity device. It is to be understood that the depth of penetration of the vehicle into the barrier system before it is brought to rest depends upon the initial engagement speed of the vehicle and its weight. The braking effort exerted by the driver of the vehicle can be ignored for all practical purposes. In all cases regardless of the direction of the vehicle it will engage and displace the units sequentially and only a predetermined unit at any one time is instantaneously accelerated to the vehicle speed thus causing a slow controlled vehicle deceleration with minimum damage to the vehicle and with minimum risk to the vehicle occupants.

Two phenomena are involved when a vehicle is stopped by the barrier system. Initially, the deceleration of the vehicle occurs because of a transfer of momentum from the vehicle to the barrier. In the final portion of the deceleration, the frictional forces become predominant. High speed photography has established that when a vehicle travelling at highway speed strikes the first unit, the unit virtually explodes. A fan of sand is thrown out from the vehicle primarily in a plane normal to the vehicle with the sand being instantaneously accelerated to approximately the vehicle speed. Since the vehicle thereafter decelerates rapidly, the sand fans out ahead of the vehicle and falls to the ground thereby dissipating its acquired energy through air resistance and sliding friction. This action continues with decreasing vigor until the vehicle no longer strikes the units with sufficient speed to throw the sand into the air. The vehicle then begins to push the remaining sand as a homogeneous unit dissipating energy directly as friction until both the vehicle and the barrier come to rest. Thus the inertia of the sand is utilized at high speeds as a decelerating agent while at the low speeds the weight and the internal and surface friction of the sand mass becomes predominant.

It is now well known that most injuries are caused by the "second collision" which occurs when the occupant strikes the interior of the vehicle after the vehicle strikes an object.

As the vehicle progresses through the barrier, it continues to strike the individual units in a series of impacts. In the initially contacted portion of the barrier system, the deceleration of the vehicle is a function of the amount of mass impacted per foot of travel. After each mpact the sand involved in that impact is displaced out of the area of impact and continues at its own post-impact velocity while the vehicle is slowed further by succeeding impacts.

The friction effects are those which occur when the vehicle stops throwing sand and begins pushing it. When the vehicle acts as a bulldozer against the mass supported by the ground, energy is lost directly to friction between the mass and the ground. Motion pictures of impacts indicate that this transition from inertial to frictional behavior occurs at around 20 m.p.h. At speeds below 20 m.p.h. the deceleration is due primarily to the friction effects.

The unique concept of utilizing unanchored frangible individual units, together with multiple impact deceleration permits the barrier system of the present invention to safely decelerate vehicles of widely different initial momentum as graphically shown in FIG. 15. As far as is known no prior barrier system which is practical for general highway use is effective to decelerate a heavy automobile at a safe rate without decelerating a lighter or more rapidly travelling vehicle at a dangerously high rate.

Once the basic concepts are fully appreciated, the particular configuration of the array lends itself to routine mathematical analysis.

If it is assumed that all of the mass of the barrier is in one unit and if it is further assumed that the collision is inelastic the reduction of vehicle speed during a single impact will be the ratio of the weight of the barrier to the weight of the vehicle. However, for a large barrier extending several yards ahead of the vehicle the collision occurs as a series of impacts rather than as a single impact. For purposes of analysis the barrier may be considered to be divided into an infinite number of infinitestimal small portions. From this the following relationship can be derived: ##EQU1## where: V_o = initial or original velocity

V_f = final velocity due to multiple successive impacts

L_n ^- 1 = "the quantity whose natural logarithim is"

M_b = mass of barrier or sand weight

M_v = mass of vehicle or car weight

If it is assumed that it is desired to decelerate a 2000 lb. vehicle from 60 m.p.h. to 0 m.p.h. and minimize the second collision, the barrier configuration is derived by first determining the total weight of the dispersible mass in the barrier system. The foregoing equation yields a figure of 5250 lbs. Next the weight of the dispersible mass in the initial unit to achieve a 10 m.p.h. reduction in speed must be determined. Using the same equation we arrive at a figure of about 400 lbs.

The size of the gap to permit the second collision to occur before the vehicle strikes the main barrier array can be determined by calculating the distance the vehicle travels at 60 m.p.h. while the occupants travel a distance of approximately 2 ft. at 10 m.p.h. In a typical case the gap should be about 12-15 ft. The length of the array of barrier units, excluding the first unit, assuming an initial speed of 60 m.p.h. and a deceleration well within the range of human tolerance will be about 18 ft.

It will be noted from FIG. 15 that the array of weights shown will safely decelerate a 2000 lb. passenger car from a speed of 60 m.p.h. with a short duration, maximum g force on the vehicle of slightly over 12 and the same array will decelerate a 3500 lb. passenger car with a maximum g force of 6.2, both rates being within the range of human tolerance without the expectation of significant injury.

Actual tests have demonstrated conclusively that the barrier system of the present invention provides for deceleration of the vehicle and its occupants by means outside the vehicle in a survivable time-distance range with or without the use of seat belts although, as in most emergency situations, the use of seat belts affords a significant added safety factor. The barrier system dramatically reduces the second collision problem by inducing a minimal speed reduction prior to the second collision after which human tolerance of high g forces is greatly increased. It has also been established that the barrier system will operate equally well on vehicles colliding at any attitude, including broadside.

A secondary, but not insignificant advantage, from the use of sand as the dispersible mass, is the substantial reduction in fire hazard. It is usually found after an arrestment that the engine compartment is liberally covered with sand which effectively inhibits the creation or maintenance of fires.

Another factor of critical importance to the successful function of the barrier system is the construction of the individual units in such a manner that they do not create a ramp effect. In most, if not all prior barrier systems, the vehicle is given a strong vertical or other undesirable acceleration perpendicular to the line of travel. As a result the vehicle often passes over the barrier with little or no loss of forward speed, is violently deflected or is overturned.

Because of the unique construction of the individual barrier units of the present invention the center of gravity of the units is located at or above the height of the center of gravity of the impacting vehicle thus eliminating entirely the ramp effect. Similarly, if the vehicle approaches the barrier system broadside it will not be tripped or overturned.

Since the entire unit is frangible, the core assembly is of light weight and crushable construction and the center of gravity of unit is artificially elevated, its function is the same as that of the barrier described above.

The functional advantage of the types shown in 12, 13 and 14 lies in the fact that the mass retention (the sand) is contained by tension forces only acting on the container skin.

The individual barrier units shown in FIGS. 12, 13 and 14 are functionally the same as the units described above.

As noted above, the depth of penetration of the vehicle into the barrier system before it is brought to rest depends on the initial engagement speed of the vehicle, and its weight. But in all cases, regardless of the direction of the vehicle, it will engage and displace the barrier units in a predetermined sequence thus providing the desired slow controlled vehicle deceleration.

The cable arrangement assists in preventing the ramp effect since the lower cable is so located as to "catch" any vehicle below the wheel centerline and the vehicle center of gravity, and the upper cable is located to intercept the vehicle above the wheel center and the center of gravity and above the bumper or body nose. As a result the vehicle is positively intercepted by the cable system and the vehicle has no tendency to rise above the system. A double cable system also insures that cables cannot slip over the nose or hood of an average vehicle which could result in injury to the vehicle occupants.

FIG. 19 illustrates another typical application of the invention.

Such an arrangement also has the advantages that a maximum free space is provided in the approaches to the object while providing, in the region closely adjacent to the fixed object, mass of sufficient size to provide full protection for the vehicle and its occupants.

From the foregoing it will be apparent that the abovestated objects and advantages of the invention have been obtained by the provision of a safety barrier for decelerating vehicles by means independent of the vehicle in a survivable time-distance range whether or not the occupants are provided with seat belts. The barrier system permits utilization of all the distance which is available in a given hazardous fixed object site making it possible to bring the vehicle to a safe stop with little or no injury to passengers and minor damage to the vehicle.

The barrier system of the present invention drastically reduces the second collision problem by inducing a minimal speed reduction to create the second collision under controlled conditions after which human tolerance to higher g forces is greatly increased. .[.The deceleration of the vehicle is not accompanied by the production of secondary hazards particularly in the form of still integral flying masses..].

.[.Most important, the barrier mass is so arranged so that no passenger car, however shaped or constructed, can climb over or nose under the barrier..].

The barrier system of the present invention has another significant advantage over known prior systems, namely, its low cost. The cost of installation of the barrier system of the present invention is nominal as compared to the costs of other highway safety devices. For example, the cost of materials used in a test installation of typical dimensions is under $1000.

The special containers used as the individual barrier units are shipped directly to the highway maintenance depot nearest the erection site. Special tools and equipment are not required for their installation, the only requirement being that the area on which the array is to be placed is reasonably level. The maintenance crew merely places the containers in position according to the pre-engineered diagram for each site and fills them with sand to the level called for. After collision, the damaged barrier units are replaced and can be refilled with the original sand, supplemented as required.