IMPACT ATTENUATOR

Abstract

A crash cushion includes first and second diaphragm frames each having first and second laterally spaced sides defining first and second planes sloping inwardly from a top to a bottom of each side of the first and second diaphragm frames. The first diaphragm frame is moveable relative to the second diaphragm frame in response to a head-on impact. The first and second side panels are attached respectively to the first and second sides of the first and second diaphragm frames, wherein the first and second side panels are moveable relative to the second diaphragm frame in response to the head-on impact. In one embodiment, the side panels may have variable cross sectional shapes along a length thereof. In addition, each frame may include a plurality of longitudinally spaced guides for engaging a rail.

Description

FIELD OF THE INVENTION

The present invention relates generally to an impact attenuator, for example a crash cushion configured with side panels moveable relative to each other.

BACKGROUND

Crash cushions have been used for many years to protect errant vehicles from rigid structures along roadways. Bridge piers, bridge abutments, light poles and other roadway appurtenances are typically shielded from errant vehicles using crash cushions. A crash cushion may perform this task primarily in at least two ways. First, an errant vehicle that impacts a crash cushion head on may be safely decelerated by compression of the crash cushion. Second, a vehicle that impacts the side of a crash cushion may be safely redirected away from the hazard in a stable manner that minimizes the chance the vehicle will subsequently roll.

While many redirective side impacts occur upstream of the protected hazard (i.e. a “right-way” impact), crash cushions may be installed between two-way or bidirectional traffic. In these situations, there exists the possibility of a reverse direction redirective side impact, whereby the impacting vehicle strikes the crash cushion after passing by the hazard. Typically, the side panels of a crash cushion are longitudinally overlapped in such a way so to prevent the vehicle from snagging on the side panels during a right-way impact. In those situations where the crash cushion has bidirectional traffic, however, there may be one side of the crash cushion where the side panels are not longitudinally overlapped in the most advantageous way to prevent vehicle snagging.

This potential for snagging may be further influenced by the traditional shape of crash cushion side panels. Typically, side panels are formed with a constant formed shape along the length of the side panel, meaning the shape and height of the corrugations does not vary from the upstream end to the downstream end of the side panel. There are several reasons for this. First, the constant cross sectional shape enables the side panels to easily stroke rearward during a vehicle head on crash impacting the front of the crash cushion. Since the cross sectional shape is constant and does not vary, overlying panels can easily stroke rearwards without interfering with an underlying downstream panel. Second, many crash side panels are formed by rolling, which results in a constant cross sectional shape from front to back.

Crash cushions configured with side panels also are typically configured with the one more of the side panels arranged in a vertical plane. Such an arrangement may not optimize vehicle roll prevention during a side impact.

Thus, the need remains for an impact attenuator that improves redirection while diminishing the possibility of vehicle roll and reducing the possibility of vehicle snagging in a reverse impact event.

SUMMARY

The present invention is defined by the following claims, and nothing in this section should be considered to be a limitation on those claims.

In one aspect, one embodiment of a crash cushion includes first and second diaphragm frames each having first and second laterally spaced sides defining first and second planes sloping inwardly from a top to a bottom of each side of the first and second diaphragm frames. The first diaphragm frame is moveable relative to the second diaphragm frame in response to a head-on impact. First and second side panels are attached respectively to the first and second sides of the first and second diaphragm frames, wherein the first and second side panels are moveable relative to the second diaphragm frame in response to the head-on impact.

In another aspect, one embodiment of an impact attenuator includes first, second and third longitudinally spaced frames. A first side panel is attached to the first and second frames, and a second side panel is attached to the second and third frames. The first and second side panels are moveable relative to the second and third frames respectively in response to a head-on impact. Each of the first and second side panels includes a first cross sectional shape at an upstream end of the side panel, a second cross sectional shape at a midpoint of the side panel and a third cross sectional shape at the downstream end of the side panel. The first, second and third cross sectional shapes are different. In one embodiment, the first, second and third cross sectional shapes have first, second and third heights, wherein the third cross sectional height is greater than the second cross sectional height. In one embodiment, the second cross sectional height is greater than the first cross sectional height.

In yet another aspect, one embodiment of a crash cushion includes first and second laterally spaced rails and first and second diaphragm frames each having first and second laterally spaced sides. At least the first diaphragm frame includes laterally spaced first and second sets of a plurality of longitudinally spaced apart guides slidably engaging the first and second rails respectively. The first diaphragm frame is moveable relative to the second diaphragm frame in response to a head-on impact. First and second side panels are attached respectively to the first and second sides of the first and second diaphragm frames, wherein the first and second side panels are moveable relative to the second diaphragm frame in response to the head-on impact.

Various methods of using and assembling the impact attenuator, or crash cushion, are also provided.

The impact attenuator, including the disclosed crash cushion, provides significant advantages relative to existing crash cushion designs. The side panels improve the performance of reverse direction redirective impacts due to the close nesting of the panels, which reduces the chances of components of the vehicle snagging on the crash cushion. The tilt of the side panels also reduces the likelihood of an impacting vehicle rolling substantially during the redirective side impacts, which subsequently also reduces the likelihood of the vehicle rolling upon exiting the crash cushion. Moreover, the side panels, and interface therebetween, increases the energy absorbed by the side panels during end on impacts through a combination of slots, tabs that break, and an interference fit between the panels as the side panels are stroked relative to each other. This innovative combination of energy absorption mechanisms works to bring the vehicle safely to a stop during end-on impacts.

The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the following claims. The various preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a crash cushion.

FIG. 2 is a side view of the crash cushion shown in FIG. 1.

FIG. 3 is an enlarged side view of the crash cushion taken along line 3 in FIG. 2.

FIG. 4 is an upstream end view of the crash cushion shown in FIG. 2.

FIG. 5 is a cross-sectional view of the crash cushion taken along line 5-5 in FIG. 2.

FIG. 6 is a cross-sectional view of the crash cushion taken along line 6-6 in FIG. 2.

FIG. 7 is a side view of one embodiment of a side panel.

FIG. 8 is an upstream end view of the side panel shown in FIG. 7.

FIG. 9 is a downstream end view of the side panel shown in FIG. 7.

FIG. 10 is a side view of another embodiment of a side panel.

FIG. 11 is a side view of another embodiment of a side panel.

FIG. 12 is a downstream perspective view of a pair of overlapping side panels.

FIGS. 13A-C are cross-sectional views taken along line 13-13 in

FIG. 12 showing the overlapping panels in progressive stages of an impact event.

FIG. 14 is an end view of a vehicle engaging one embodiment of an impact attenuator in a side impact event.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

It should be understood that the term “plurality,” as used herein, means two or more. The term “longitudinal,” as used herein means of or relating to length or the lengthwise direction 2 of the crash cushion, or assembly thereof, and includes an axial, end-on impact direction. During an end-on impact, the system dissipates the energy of the impacting vehicle. The term “lateral,” as used herein, means directed between or toward (or perpendicular to) the side of the crash cushion, for example the lateral direction 5, or a side impact direction. The term “coupled” means connected to or engaged with, whether directly or indirectly, for example with an intervening member, and does not require the engagement to be fixed or permanent, although it may be fixed or permanent, and may include an integral connection wherein the features being coupled are portions of a single, unitary component. The term “transverse” means extending across an axis, and/or substantially perpendicular to an axis. It should be understood that the use of numerical terms “first,” “second,” “third,” etc., as used herein does not refer to any particular sequence or order of components; for example “first” and “second” side panels may refer to any sequence of such side panels, and is not limited to the first and second side panels of a particular configuration unless otherwise specified. The terms “upstream” 400 and “downstream” 402 refer to directions relative to the impact direction of a vehicle, for example with a backstop 30 and/or rear anchor 416 being downstream of the front anchor 404, or front of the crash cushion. The terms “inboard” and “outboard” are defined in the lateral direction relative to a centerline longitudinal axis 482, with “inboard” referring to a component or feature being closer to the centerline axis 482, and “outboard” referring to a component or feature being further from the centerline axis. The phrase “impact attenuator” refers to a structure, assembly and/or system that absorbs or attenuates the energy of an impacting vehicle, whether in a head-on, right-way or wrong-way side redirective impact event. The impact attenuator includes two-sided crash cushions, and one-sided guard rail systems.

Referring to FIGS. 1-4, an impact attenuator is configured as a crash cushion 100 having a base track 8, which is used to mount the crash cushion to the roadway 408, including a shoulder and/or median thereof, or other suitable foundation. The rear of base track 8 is attached to a backstop 30 at a downstream end of the crash cushion. The base track 8 may include a plurality of plates secured to the roadway, including a front anchor plate 404 and a plurality of longitudinally spaced anchor plates 412, for example with fasteners 414 and/or adhesives, and a pair of laterally spaced rails 420 secured to the anchor plates 404, 412, 416. In one embodiment, shown in FIGS. 5 and 6, each rail 420 has an outboard facing C-shape defined by upper and lower flanges 422, 424, with the upper flange 424 defining a support surface, or track. The crash cushion includes a plurality of diaphragm frames 7, configured with guides 12 that slide on the base track 8, and the rails 420 in particular. The frames 7 are longitudinally spaced apart at a predetermined distance. A forwardmost/upstream diaphragm frame 11 is positioned near the upstream/front end of the base track 8. A directional placard 17 may be mounted on the front face of the first diaphragm frame 11 to provide a flat surface where reflective markings may be applied and positioned. The placard 17 may be secured to the diaphragm with fasteners 31. The first diaphragm frame 11, and remaining plurality of diaphragm frames 7, are each positioned and engaged with the laterally spaced rails 420 by a plurality of longitudinally spaced guides 12.

A plurality of side panels 13, 14, 15, and 16 are connected to, and extend longitudinally between adjacent pairs of diaphragm frames 11, 7, thereby defining and forming bays 101. The side panels 13, 14, 15, 16 may be connected to both sides 430, 432 of the frames 11, 7, or to only one side, for example a post of a guardrail system. In addition, a plurality of side panels 13, 14, 15, 16 may be connected to each side of each pair of adjacent frames 11, 7. For example, as shown in FIGS. 1-4, a pair of vertically spaced side panels 13, 14, 15, 16 are connected to each side of each pair of frames 11, 7. The lower edge of an upper side panel may be vertically spaced from an upper edge of a lower side panel, as shown in FIG. 3. The crash cushion 100 shown in FIG. 1 has 8 bays 101, although different embodiments of crash cushion 100, may have more or less bays 101, resulting in a corresponding greater or lesser number of diaphragm frames 7 and side panels 13, 14, 15, and 16. The side panels 13, 14, 15, and 16 are designed to absorb different amounts of impact energy and their respective numbers may vary in a particular design of crash cushion 100, depending upon the specific application. The rearwardmost, downstream side panels 14, which form the rearwardmost, downstream bay 101, are connected to end panels 21, which in turn are connected to the backstop 30.

Referring to FIGS. 3, 5 and 6, the side panels 15, 13 may be held in place, and secured to opposite sides 430, 432 of the diaphragm frame 7 at the downstream end with a flat washer 1 and fastener 6, configured as a bolt in one embodiment. At the upstream end, the side panels 15, 13 are held in place by a flat washer 20 and fastener 6. Each diaphragm 11, 7 includes a plurality of longitudinally spaced guides 12, which are secured to the diaphragm with fasteners 4, shown as bolts, and are longitudinally spaced apart by and with spacers 32, which may be configured as washers, for example steel washers. The fasteners 4 extend through a pair of longitudinally spaced mounting plates 434, connected to opposite faces of each diaphragm frame 11, 7, the spacers 32 and the guides 12. In one embodiment, each diaphragm frame 11, 7 includes a plurality, shown as three, guides 12 on each side 430, 432, with two spacers 32 disposed between the guides 12. It should be understood that there may be more or less guides 12, and more or less spacers 32, or no spacers 32. Fasteners 4 also fix diaphragm guides 9 to the diaphragm frames 11, 7. The diaphragm guides 9 engage the top surface of the rails 420, and the upper flange 424 in particular, and help align the diaphragms 7, 11 in an upright orientation during end-on impacts, where the diaphragm frames 11, 7 move in a downstream direction. The guides 9 support the frames 11, 7 on the rails 420, and slide along the rails during the impact. The guides 12 have in inboard facing C-shape, defining a groove 444 that is shaped to receive the upper flange 424 of the rail 420. The guides 12 include a lower arm 442 that bears against a lower surface of the upper flange 424 to prevent the frames 11, 7 from being lifted off the rail 420 both during a head-on and side impact event. The plurality of guides 12 separated by spacers 32 assists in maintaining a longitudinal sliding motion of the frames 7 without binding. This is achieved by a geometric angular allowance laterally between the frames 7 and the base track 8. The plurality of relatively thin guides 12 and the liberal “C” shaped jaw of the guides 12 aids in the longitudinal system stroke of each frame. In one embodiment, the guides 12 may have a thickness between and including ¼ inch to 1 inch, and may have a thickness of ½ inch in one embodiment, although it should be understood that other thicknesses may be suitable.

Referring to FIGS. 4-6 and 14, the diaphragm frames 11, 7 and the first and second laterally spaced sides 430, 432 thereof, define first and second planes P1, P2 sloping inwardly from a top 450 to a bottom 452 of each side 430, 432 of the first and second diaphragm frames. Correspondingly, the outer surface of the side panels, connected to the sides 430, 432, also form third and fourth planes P3, P4 sloping inwardly from a top to a bottom of each side. A plurality of side panels 13 are connected to each of the sides 430, 432 of the frames 7. In one embodiment, the planes P1, P2, P3, P4, and side panels 13 parallel thereto, are oriented at an angle β to a vertical axis. The angle β may be between zero and 15 degrees, and preferably between 0 and 10 degrees, and preferably 5 degrees in one embodiment.

Referring to FIGS. 7-9, one embodiment of a side panel 13, 15 has an upstream end 105 and a downstream end 106. The side panel may be configured with a W-shape having a pair of crests 124 separated by a valley 127 and upper and lower flanges 470, 472, which define upper and lower surfaces of the side panels, with the upper and lower surfaces being linear between the upstream and downstream ends of the side panel.

The upstream end 105 of side panel 13, 15 has a mounting hole 107 to facilitate attaching the side panel 13, 15 to an upstream diaphragm frame 7. The downstream end 106 of side panel 13, 15 has partial mounting hole 110 for mounting the downstream end 106 of the side panel 13, 15 downstream to an adjacent diaphragm frame 7. A slot 108 is positioned in the center of the side panel 13, 15 and acts as a guide for the fastener 6 as the side panel 13, 15 is stroked during an end-on impact. The partial mounting hole 110 is joined to the slot 108 by a restriction opening 109, or narrower neck portion of the slot. The restriction 109 acts to hold the side panel 13, 15 in a fixed location until a predetermined force is achieved during the axial head-on impact. In this embodiment, the restriction 109 narrows the partial mounting hole 110 to a ½ inch, however this distance may be greater or lesser, depending upon the level of predetermined load that is desired. As shown in FIG. 7, the partial mounting hole 110 has the same diameter as the width of the slot 108, however in other embodiments, the dimensions may be different. The downstream end 106 of the side panel 13, 15 includes a tab 111. During an impact event, where the side panel 13, 15 is being stroked downstream, the tab 111 prevents the downstream end 106 of the side panel 13, 15 from being caught under the flat washer 20 of a next adjacent downstream panel.

The side panel 13, 15 has a first cross sectional shape A1 at an upstream end 105 of the side panel, a second cross sectional shape A2 at a midpoint of the side panel and a third cross sectional shape A3 at the downstream end 106 of the side panel, wherein the first, second and third cross sectional shapes A1, A2, A3 are different. In one embodiment, the first, second and third cross-sectional shapes A1, A2, A3 have first, second and third heights, and wherein the third height H3 is greater than the second height H2, and the second height H2 is greater than the first height H1. In one embodiment, the side panel 13, 15 has a constant thickness (e.g., 3/16 inches), and a constant width W (e.g., 2 11/16 inches), but the upstream end 105 has a first height H1, the midpoint has a second height H2, and the downstream end 106 has a third height H3, wherein the third height H3 is greater than the second height H2, and the second height H2 is greater than the first height H1. In one embodiment, the outer dimension of the upstream end of crests 124 of the side panel 13, 15 is 3 11/16 inches, while the panel has an overall length of 32 inches. It should be understood that the side panels may have other suitable shapes and sizes. The other side panels 14, 16 may be configured with similar cross-sectional shapes A1, A2, A3 and heights H1, H2, H3. It should be understood that the phrase “cross sectional shape” refers to the shape of the cross section, including for example and without limitation the height, width, web thickness, depth of the valleys/peaks, etc. at the cross section, and does not equate to area, although the areas may also be different or the same.

Referring to FIG. 9, a downstream end of the side panel 13, 15 is shown. The inner dimension of the downstream end of the valleys 125 defined by the crests 124 of the side panel 13, 15 may be 4 inches in one embodiment. The side panel 13, 15 has a non-constant cross-sectional shape from one end to the other as just explained, and this is the reason for the larger dimension of the valley 125 of the downstream end of the side panel 13, 15 versus the crest 124 of the upstream end. The thickness of the material forming the side panel 13, 15, which is 3/16 inches in one embodiment, may be made of thicker or thinner material. In one embodiment, the components making up the system, including the panels, frames and guides are made of galvanized steel, although other materials may be suitable.

As shown in FIG. 10, the side panel 16 has an upstream end 135 and a downstream end 136. The upstream end 135 includes a mounting hole 137 and the downstream end includes a mounting hole 140. Between the mounting hole 137 and the mounting hole 140 lie a plurality of elongated slots 138 and a shorter slot 142. The slots 138, 142 are separated by tabs 143. The mounting hole 140 is separated from the short slot 142 by a starter tab 139. The starter tab 139 holds the side panel 16 in a fixed location until a predetermined force is achieved during an axial, head-on impact.

Referring to FIG. 11, a side panel 14 includes an upstream end 155 and a downstream end 156. The upstream end 155 includes a mounting hole 157 and the downstream end includes a mounting hole 160. Between the mounting hole 157 and the mounting hole 160 lies slots 162. The slots 162 are separated by tabs 163. The mounting hole 160 is separated from the slot 162 by a starter tab 159. The starter tab 159 acts to hold the side panel 14 in a fixed location until a predetermined force is achieved during an axial, head-on impact.

Referring to FIG. 12, side panels 15, 13, 16, 14 are overlapping, with the downstream end 106, 136, 156 of the side panel 15, 13, 16, 14 overlapping the upstream end 105, 135, 155 of an adjacent downstream side panel 13, 16, 14. The side panels 15, 13, 16, 14 are joined together by fastener 6 and flat washer 1 and to the frame 7. Likewise, a fastener 6 and flat washer 1 fix the upstream end of the side panel 15, 13, 16, 14 to another diaphragm frame 11, 7.

Referring to FIGS. 13A-C, the cross-sectional shape of the overlapping side panels 15, 13, 16, 14 is shown at a different point in time during an end-on impact event. FIG. 13A shows an initial orientation of side panels 15, 13, 16, 14. In this orientation the inside surface 185 of a crest 125 of the side panel 15, 13, 16, 14 rests against the outside surface of a crest 124 of the side panel 13, 16, 14. There is no gap between these two surfaces due to the non-constant cross-sectional shape of side panels 15, 13, 16, 14, with the downstream end of a first panel nesting in the upstream end of a second panel. There is a gap, however, between the outer surface of an inclined edge/web 176 of the side panel 13, 16, 14 and inside surface of an inclined edge/web 186 of the side panel 15, 13, 16, 14.

Referring to FIG. 13B, the overlapping joint is shown at a later point in time during an end-on impact event, where the side panel 15, 13, 16, 14 has moved downstream relative to the side panel 13, 16, 14. At this point in the impact event, the gap between the surfaces of the inclined edges/webs 176 and 186 has closed and the two surfaces have begun to bear against each other. This causes the panels 15, 13, 16, 14 to deform, absorbing some of the energy of the impacting vehicle. This deformation of the panels further leads to the inside surface of the valley 185 moving away from the outside surface of the crest 124.

In this way, the impact attenuator includes first longitudinally spaced frame 11 and second and third longitudinally spaced frames 7, a first side panel 15 attached to the first and second frames, and a second side panel 13 attached to the second and third frames, wherein the first side panel 15 is moveable relative to the second side panel 13 from a pre-impact position to an impact position in response to a head-on impact. The downstream end 106 of the first panel 15 overlaps the upstream end 105 of the second panel 13 in a non-interference configuration in the pre-impact position, as shown for example in FIG. 13A. The downstream end 106 of the first panel 15 overlaps the downstream end 106 of the second panel 13 in an interference configuration in the impact position as shown for example in FIG. 13C. The phrase “interference configuration” refers to the interface between two components causing deformation (elastic or plastic) of one or both of the components (e.g., first and second side panels 15, 13), with the phrase “non-interference configuration” referring to a lack of any deformation of either component due to the interface or positional relationship between the two components. As discussed herein, the shapes of the side panels may be differentiated to cause the interference configuration as the side panels are moved relative to each other from the pre-impact position to the impact position.

Referring to FIG. 13C, the side panel 15, 13, 16, 14 has completed its movement relative to the side panel 13, 16, 14. At this point, the fastener 6 and flat washer 1 attached to a frame 11, 7 have moved downstream, so they are adjacent to fastener 6 and flat washer 1 of the next downstream frame 7. At this point in the impact event, the edges/webs 176 and 186 bear against each other with a high load, which causes significant deformation of the panels 15, 13, 16, 14, absorbing additional energy of the impacting vehicle 201. This deformation of the panels further leads to the inside surface of the valley 185 moving further away from the outside surface of the crest 124.

As shown in FIG. 14, an impact of a vehicle 201 with the side of the crash cushion 200. The sides of the crash cushion 200 are tilted at an angle of β from a vertical axis. The impact of the vehicle 201 with the crash cushion 200 results in a roll angle δ with the horizontal.

Operation

One method of redirecting a vehicle impacting the side of a crash cushion includes impacting the side panel 15, 13, 16, 14 with a vehicle 201, wherein the side panel is attached to sides of adjacent first and second diaphragm frames 11, 7 each defining the plane P1, P2 sloping inwardly from a top to a bottom of the sides of the first and second diaphragm frames. The first diaphragm frame 11, 7 is moveable relative to the second diaphragm frame 7 in response to a head-on impact, and the side panel 15, 13, 16, 14 is moveable relative to the second diaphragm frame 7 in response to the head-on impact. The method further includes redirecting the vehicle 201 with the side panel(s) 15, 13, 16, 14.

Another method of attenuating energy of a vehicle impacting a crash cushion includes impacting the crash cushion head on and moving a first frame 11, 7 relative to a second frame 7 and a third frame 7, wherein the first, second and third frames are longitudinally spaced. The method further includes sliding a first side panel 15, 13, 16, 14 attached to the first and second frames relative to a second side panel 1316, 14 attached to the second and third frames, wherein each of the first and second side panels comprises a first cross sectional shape A1 at an upstream end of the side panel, a second cross sectional shape A2 at a midpoint of the side panel and a third cross sectional shape A3 at the downstream end of the side panel, wherein the third cross sectional shape A3 is different than the second cross sectional shape A2. In one embodiment, the third cross sectional shape A3 has a height H3 that is greater than the height H2 of the second cross sectional shape A2.

A method of attenuating energy of a vehicle impacting a crash cushion head on includes moving a first frame 11, 7 relative to a second frame 7, wherein the first and second frames are longitudinally spaced, and wherein the first frame includes a plurality of longitudinally spaced apart guides 12. The method further includes sliding the guides 12 and first frame 11, 7 relative to a rail 420 supporting the first frame 11, 7, wherein the guides 12 are engaged with the rail 420. The method further includes sliding a side panel 15, 13, 14, 16 attached to the first frame relative to the second frame.

Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. As such, it is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it is the appended claims, including all equivalents thereof, which are intended to define the scope of the invention.

Claims

1. A crash cushion comprising: first and second diaphragm frames each comprising first and second laterally spaced sides defining first and second planes sloping inwardly from a top to a bottom of each side of the first and second diaphragm frames, wherein the first diaphragm frame is moveable relative to the second diaphragm frame in response to a head-on impact: andfirst and second side panels attached respectively to the first and second sides of the first and second diaphragm frames, wherein the first and second side panels are moveable relative to the second diaphragm frame in response to the head-on impact.

2. The crash cushion of claim 1 further comprising first and second laterally spaced rails, wherein at least the first diaphragm comprises first and second sets of a plurality of spaced apart guides slidably engaging the first and second rails respectively.

3. The crash cushion of claim 2 further comprising a spacer disposed between adjacent pairs of the spaced apart guides in each of the first and second sets.

4. The crash cushion of claim 3 where each set comprises three guides, and further comprising two of the spacers disposed between the adjacent pairs of guides in each set.

5. The crash cushion of claim 1 wherein each of the first and second side panels comprises a first cross sectional shape at an upstream end of the side panel, a second cross sectional shape at a midpoint of the side panel and a third cross sectional shape at the downstream end of the side panel, wherein the first, second and third cross sectional shapes are different.

6. The crash cushion of claim 5 wherein the first, second and third cross-sectional shapes have first, second and third heights respectively, wherein the third height is greater than the second height.

7. The crash cushion of claim 6 wherein the second height is greater than the first height.

8. The crash cushion of claim 7 wherein the width of each of the first and second side panels is the same at the upstream end, the midpoint and the downstream end.

9. The crash cushion of claim 6 wherein the upper and lower surfaces of each of the first and second side panels are linear.

10. The crash cushion of claim 6 wherein each of the first and second side panels comprises a W-beam.

11. The crash cushion of claim 1 comprising a third diaphragm frame positioned downstream of the second diaphragm frame, wherein the third diaphragm frame comprises first and second laterally spaced sides defining first and second planes sloping inwardly from a top to a bottom of each side of the third diaphragm frame, wherein the second diaphragm frame is moveable relative to the third diaphragm frame in response to a head-on impact: and third and fourth second side panels attached respectively to the first and second sides of the second and third diaphragm frames, wherein the third and fourth side panels are moveable relative to the third diaphragm frame in response to the head-on impact.

12. An impact attenuator comprising: first, second and third longitudinally spaced frames; anda first side panel attached to the first and second frames, and a second side panel attached to the second and third frames, wherein the first and second side panels are moveable relative to the second and third frames respectively in response to a head-on impact, wherein each of the first and second side panels comprises a first cross sectional shape at an upstream end of the side panel, a second cross sectional shape at a midpoint of the side panel and a third cross sectional shape at the downstream end of the side panel, wherein the first, second and third cross sectional shapes are different.

13. The impact attenuator of claim 12 further comprising a rail, wherein at least the first frame comprises a plurality of spaced apart guides slidably engaging the rail.

14. The impact attenuator of claim 13 further comprising a spacer disposed between adjacent pairs of the spaced apart guides.

15. The impact attenuator of claim 14 where the plurality of spaced apart guides comprises three guides, and further comprising spacers disposed between the adjacent pairs of guides.

16. The impact attenuator of claim 12 wherein the upstream end has a first height, the midpoint has a second height, and the downstream end has a third height, wherein the third height is greater than the second height.

17. The impact attenuator of claim 16 wherein the second height is greater than the first height.

18. The impact attenuator of claim 17 wherein the width of each of the first and second side panels is the same at the upstream end, the midpoint and the downstream end.

19. The impact attenuator of claim 16 wherein the upper and lower surfaces of each of the first and second side panels are linear.

20. The impact attenuator of claim 12 wherein the side panel comprises a W-beam.

21-27. (canceled)

28. An impact attenuator comprising: first, second and third longitudinally spaced frames; anda first side panel attached to the first and second frames, and a second side panel attached to the second and third frames, wherein the first side panel is moveable relative to the second side panel from a pre-impact position to an impact position in response to a head-on impact, wherein the first panel comprises a downstream end overlapping an upstream end of the second panel in a non-interference configuration in the pre-impact position, and wherein the first panel comprises a downstream end overlapping the downstream end of the second panel in an interfering configuration in the impact position.