GB2238562A - Process for inserting a rumble strip in a road - Google Patents

Abstract

A process for inserting a rumble strip in a road comprises cutting a groove in the road by means of a reflex-percussion machine (in which the cutting bit is forcibly withdrawn from the surface the instant the bit strikes the surface, so that the material flakes by induced tension), inserting the strip of elastomeric material in the groove, providing a means for constraining the strip within the groove, and finally sealing the strip and strip-securing means within the groove.

Description

RUMBLE STRIP FOR HIGHWAYS This invention relates to the provision of rumble strips and the like in highways.

Rumble strips are strips which are placed across one or more lanes of a highway at the approach to a road junction or other hazard. The rumble strips are provided where it is deemed desirable to present drivers with an audible warning, that they may be especially alerted to the hazard. As the vehicle runs over the rumble strips, the driver hears a rumbling noise. The driver also "feels" a physical change in the road surface, which also serves to alert him.

Practice varies somewhat, but typically the rumble strips are arranged in four groups of eight or ten strips, positioned 80, 60, 40, and 20 metres from the hazard.

BACKGROUND TO THE INVENTION One of the major problems with rumble strips, as with other road hazard markings, is that anything that protrudes, even slightly, above the surface of the roadway imposes a very tight restriction on the use of snow plows.

The impact of a snow plow blade against a rumble strip cannot be allowed to be too vigorous, or the rumble strip will be damaged -- and, perhaps even worse, the edge of the snow plow blade also may be damaged. If the snow plow is moving at any significant speed when the impact occurs, and if the damage takes the form of pieces being broken from the rumble strip, or from the blade, the broken pieces may be hurled at other road users.

On the other hand, if the rumble strips are so smooth and gentle that a snow plow blade passes easily over the strips, then the problem arises that the passage of the tires of vehicles may not produce enough rumble intensity to perform the primary function of alerting the driver.

A conventional rumble strip comprises a narrow mound of asphalt. This mound is perhaps 1 cm high above the road surface at its midpoint, and is typically 15 cm wide, being feathered into the surface at the leading and trailing (front and rear) edges. The rumble strip is applied to the road surface after the surface itself has been flattened.

Such simple rumble strips are caused to adhere to the road surface basically by means of an adhesive. The adhesive is not as strong as the asphalt, and asphalt itself, while of course having very good bulk strength, is not at all strong when in the form of feathered edges. Also, the rumble strip inevitably is subject to accentuated wear, simply because the strip does protrude above the road surface. For these reasons, rumble strips in the form of asphalt mounds tend to break up, and they are not well regarded by highway engineers.

In place of asphalt, mounds of concrete have been used, especially on concrete roads, but concrete is little better than asphalt in this regard.

It has been proposed to cut a groove, with a saw, in the road surface, and to secure a strip of rubber in the groove.

The problem here lies in the fact that, although the saw-cut groove may be perhaps 2 cm deep, the width of the groove, as produced by the saw blade, is very limited, the maximum groove width being of the order of 5 mm or so. The result of this limitation is that only very small, flimsy, pieces of rubber can be used. If the groove is widened by the process of repeatedly passing the saw along the groove, it becomes very difficult to hold the width of the groove accurately constant along its length, with the result, if that method were used, that sometimes the rubber would work loose.

GENERAL FEATURES OF THE INVENTION In the invention, the rumble strip comprises a strip of rubber, but unlike the flimsy rubber strips associated with narrow saw-cut grooves, the rubber strip in the invention is several centimetres, as much as 5 or 10 cm, wide, and is correspondingly deep. In the invention, the groove in the road surface, for receiving the rubber rumble strip, is not cut by means of a saw but is cut by the ref)ex-percussion process, and preferably by the modification of the reflex percussive process in which the cutting tool does not rotate.

British patent publication number GB-2215257 (CLARRE, Sept 1989) shows how the reflex-percussion process may be carried out with non-rotating cutting bits.

Such a process, it has been found, is very effective in cutting deep wide grooves in concrete and asphalt. The resulting grooves are tremendously accurate as regards constancy of width. Also the cut is very clean, and the lips or edges of the groove are quite sharp. The base of the groove, as cut, is easy to control accurately as to its depth, and the surface finish which it is possible to achieve on the base of the groove would be virtually unobtainable by any other (cutting) process, even if cost were no object.

In a groove cut by the reflex-percussion process the edges of the groove tend to be strong, and the junction between the walls and the base of the groove can be at a sharply defined angle (generally a right-angle). The process is highly controllable. The process causes only a minimum of damage in and around the groove cavity, both as regards the avoidance of gross cracks, and also as regards the avoidance of microfracturing.

Notwithstanding these benefits of accuracy, the process is relatively fast: other methods of removing material from a groove of the above dimensions, such as the use of a jack hammer, are much slower.

In the invention, the reflex-percussive process is essential for cutting the grooves. It is not essential that the cutting bit does not rotate. However, the resulting loss of accuracy, and slowness, when a rotating bit is used, make that variation of the process much less attractive, and it is therefore preferred that the bit be constrained against rotation. In explanation of this preference, it may be noted that when the bit does not rotate, as shown in CLARKE, the bit may be designed with a row of cutting teeth along its edge, and it is this row which produces the side wall of the groove. When the bit rotates, there is not the same concentrated cutting action on the side walls.

In the invention, it is recognized that the groove which results from the reflex-percussive process is accurate enough as regards the width of the groove to enable a preformed rubber strip to be inserted and securely held in the groove. If the groove were inaccurate, and if the attempt were made to fill the resulting irregularities and voids with adhesive or sealing compound, it is recognized that the risk would be too high that the rubber strips might work loose.

It is recognized also that the reflex-percussive process produces a groove which is wide enough to accommodate a worthwhile width of rubber strip, for example 5 or 10 cm, as distinct from the thin, flimsy rubber strips which were all that could be accommodated in saw-cut grooves. The depth of the groove preferably should be at least half its width.

The invention lies in the recognition of the usefulness of the reflex-percussion process for cutting the grooves for rubber rumble strips. It is recognized that the process provides wide, accurate grooves very economically, so much so indeed that it becomes economically practical to use bulky pieces of rubber as the material for the strips.

Without the reflex-percussion process to cut the grooves, there would be no economical way to make the grooves accurate enough and wide enough; and without wide, accurately-cut grooves, large rubber strips cannot be used.

It may be noted also that the accuracy of the depth of the groove is hardly less important than the accuracy of the width, and again, reflex-percussion gives an excellent degree of accuracy as regards the groove depth.

There are other ways of making wide, accurate grooves: for example, by excavating a large trench, and filling the trench with concrete into which the groove is moulded.

However, such a procedure would out of the question on cost grounds for rumble strips. It is possible to cut the two side walls of a wide groove fairly accurately by using ganged saws, and by then removing the material between the saw cuts with a jack hammer. This procedure, however, is not so economical as reflex-percussion, and in any case the floor of the groove in that case cannot be controlled accurately.

The ability, with reflex percussion, to control the depth of the groove accurately, and the ability to obtain a smooth flat surface to the bottom of the groove, are important contributing factors in the usefulness of the reflex percussion process in the invention.

With the invention, rumble strips can be installed quickly and easily. The grooves are cut in one pass, and the strips are preformed in the factory and are suitable for immediate on-site insertion into the grooves. If the grooves are arranged in the usual four groups, the lane need be closed (for the work to be done) only for a few hours.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT By way of further explanation of the invention, an exemplary embodiment of the invention will now be described with reference to the accompanying drawings, in which: Fig 1 is a lateral cross-section across a lane of a roadway in which a groove is being cut by a reflex-percussion machine; Fig 2 is a section corresponding to that of Fig 1A, showing the use of a different machine; Fig 3 is a plan view showing one relationship of the cutting bits of the machine of Fig 1 to a groove; Fig 4 is a view corresponding to Fig 3, showing an alternative relationship; Fig 5 is a cross-section taken along the length of the roadway of a completed groove, into which has been inserted a rubber strip; Fig 6 is a section corresponding to Fig 5, showing a different rubber strip;; Fig 7 is a section corresponding to Fig 5, showing another form of the groove, and a different rubber strip; Fig 8 is a lateral cross-section across the lane, corresponding to Fig 1, showing the completed groove and inserted strip of Fig 7; Fig 9 is a section corresponding to Fig 8, showing a different configuration of the lane.

The apparatus shown in the accompanying drawings and described below are examples which embody the invention. It should be noted that the scope of the invention is defined by the accompanying claims, and not necessarily by specific features of exemplary embodiments.

Fig 1 shows two cutting heads of a reflex-percussion groovecutting apparatus 2, in the process of cutting a groove 3 aoross the width of a lane of a roadway.

The apparatus 2 is generally similar to that shown in CLARE. The construction and operation of one of the cutting heads 4 will now be described. A hammer 5 is grooved along its downward-facing surface, and a series of bits 6, in the form of cross-bars, are let into the grooves, and are fixed therein. The hammer 5 is fixed to the nose 7 of a piston 8, in such a manner that, during operation, the hammer is unitary with the piston.

The piston 8 is able to reciprocate in a cylinder 9, the cylinder being formed in a block 10. The piston 8 is provided with a head 12; the head is eccentric with respect to the rest of the piston, and is reciprocable in a complementary eccentric bore formed in the block 10. By virtue of the eccentric arrangement, the piston may reciprocate freely in the cylinder, but the piston is constrained against rotation.

Ports are formed in the block 10; a pressure port 14, which is connected to a source of compressed air, and an exhaust port 16, which is open to the atmosphere. When the piston is at the top of its stroke, air from the port 14 flows into the annular space 18, through the hole 20 to the centre passage 23, and into the chamber 25. The pressure then acts on the head 12 of the piston, driving the piston downwards.

The piston descends to the position shown in Fig 1. Now, air flows from the chamber 25, through the passage 23, through the hole 27, and out through the exhaust port 16.

Supply air enters the annular space 18, driving the piston back up, and the reciprocating cycle is complete.

Typically, a reflex percussion hammer strikes 1400-1800 blows per minute.

It should be noted that, in accordance with the principles of reflex percussion, the piston (together with the hammer 5) does not bounce against the bottom of the groove 3: rather, the piston is forcibly pulled clear of the groove just as the blow is struck.

The shock wave from the blow travels into the material of the roadway, and is reflected back. But, when the shockwave is reflected back to the surface of the material, there is no massive anvil present to resist the shockwave, and it is the resulting induced tension which fractures the material into small flakes or pieces.

It is the forced retraction of the piston which ensures that the hammer is clear before the shock wave is reflected. In an apparatus such as a jack hammer, where the anvil simply bounces clear, it is in fact the reflected shock-wave itself which causes the anvil to bounce. The mass of the anvil, which is in contact with the material at that moment, abosorbs the returning shock wave and prevents tension being induced in the material. A jack hammer cuts by a penetrating, crushing action: a reflex-percussion machine, by virtue of the forced withdrawal of the hammer, cuts by inducing the material to fracture itself.

In use, the block 10 is located over the place where the groove 3 is to commence, and the block is lowered until the cutting bits 6 contact the surface of the roadway. As the block is lowered further, the piston 8 is forced upwards; reciprocatory vibration commences, and the bits start to cut down into the roadway. As the block descends still further, the other piston 29 is pushed upwards until the moment comes when it too starts to reciprocate. When the cutting heads have cut down to the depth level shown in Fig 1, the descent of the block is checked, and the block is set to traverse horizontally to the right, thereby progressively cutting the groove.

Preferably, the groove 3 is cut in a single pass. Thus, the bits 6 preferably should extend across the full width of the groove. However, in order to keep the mass of the hammers down, which is desirable in order to maintain a fast rate of reciprocation, the designer may prefer not to have a bit width of more than 5 cm. If the groove width is to be 10 cm, the designer may provide double the number of hammers, and arrange them in staggered formation. Then, each hammer may be relatively light; and each hammer has its own piston, and may reciprocate independently of the others.

Figs 3 and 4 show different ways of arranging the stagger of the bits relative to the groove, in cases where a stagger is required.

Alternatively, when the cutting head can be accurately guided in its traverse, it is permissible to cut a wide groove by taking two, or more, passes.

Fig 5 shows a rubber strip fitted into the completed groove.

The grooves and strips are arranged in parallel, across the road, at the approach to a hazard, such as a road junction.

The rubber strip 30 is preformed, for example as an extrusion, having the same cross-section at all points along its length. The strip 30 may include holes 34, which are included as part of its extruded form. The material of the strip 30 may be neoprene of the non-interconnected cell type.

To install the rubber strip 30 in the groove 3, first the base 36 and walls 38 of the groove are liberally smeared with a suitable adhesive, or sealant/adhesive, material, preferably a one-part, moisture-curing, polyurethane and hydrocarbon solvent mixture. Then the strip is pressed down into the groove. The groove and strip should be of complementary widths, whereby the strip is a tight fit in the groove, and in fact has to be hammered in.

The rubber strip 30 is formed with a slightly convex upper surface 40, which is so dimensioned as to protrude slightly above the road surface after installation. Such holes 34 as are present are arranged so that the strip will have suitably resilient characteristics of depression when a tire rolls over the strip.

The strip 30 should not provide too much of an obstacle to a light vehicle such as a motor-cycle and yet the strip should provide sufficient intensity of rumble as to alert the driver of a heavy truck. By selecting a suitable grade of rubber, and by suitable dimensioning and positioning of the holes 34, the strip can be given a rate characteristic that is variable, whereby a light load will easily deflect the strip down to the level of the road surface 43, whereas a much heavier load is needed to deflect the strip further down below the surface.

In the version shown in Fig 6, a spacer 45 (made of metal, or a hard plastic) is included, the purpose of which is to allow the spring-characteristics of the strip 47 to be more accurately controlled.

In Fig 7, the rubber strip 49 is not held (or not held exclusively) by means of the sealant/adhesive. In Fig 7, a channel 50 is cut into the floor 52 of the groove 3. The channel 50 preferably is also cut by the reflex-percussion process.

Into the channel 50, an anchor strip 54, made of aluminum for example, is secured by means of bolts 56. The bolts engage with the material of the roadway (asphalt, concrete, etc) and are of the self-expanding type.

The anchor strip 54 is formed with a Tee-shaped head 58, and the rubber strip 49 is formed with a complementary Teeshaped slot.

The mechanical connection established by the interaction between the rubber strip and the anchor strip makes the strip even more secure within the groove than it was with the adhesive as previously described. It certainly is important that the rubber strip should never be allowed to become detached from the groove, and the mechanical connection provides even greater security from that standpoint.

The profile of the rubber strip 49 may be provided with holes, as at 60, by means of which the deflection characteristics may be optimized.

In the arrangement of Fig 7, the rubber strip has to be assembled by sliding the strip onto the Tee-head 58 along the length of the strip, ie across the width of the road.

Access must be provided at one end of the strip to enable assembly to be accomplished in this way. Fig 8 shows how this may be done in the case of a country road with no sidewalk or kerb, but where the side of the road slopes away into a grass verge. The road surface 63 is generally a few centimetres above the level 65 of the verge, or it is in any event a simple matter to excavate the verge locally to provide access to the (sloping) edge 67 of the asphalt or concrete.

As may be inferred from Fig 1, when the operation of cutting the groove stops, the right hand end of the finished groove has a run-out, whereas the left hand end (ie the end of the groove which was formed first) is more nearly vertical.

Preferably, therefore, the groove should be started at the middle of the road and should be cut towards the side of the road, where the run out can be accommodated. Thus, if in Fig8 the groove is started at the end 69 near the middle of the road, the end 69 can be almost sharply vertical, and therefore the rubber strip may be pushed almost to the very end of the groove. The small space between the end of the rubber and the end 69 of the groove may be filled with a suitable sealant and filler material.

The other end of the groove is at the side of the road, and the rubber may be trimmed off to suit: again the space at the end of the groove is filled in with filler.

In the Fig 9 case, a kerb 70 is present at the side of the road. Therefore the groove cannot run out, as was possible in Fig 8. The right hand end 74 of the groove has a much more gradual slope than the left hand end. There is no difficulty in feeding the rubber strip onto the Tee-head from the right hand end, since the strip is flexible enough to bend around the kerb. Again the ends of the groove, beyond the rubber, are filled in -- with a bulk filler such as asphalt if the voids are large enough.

When a snow plow blade strikes the rubber strip, the impact is easily absorbed without either the strip or the blade being damaged. The blade rises up slightly, and the strip descends slightly. The shock-absorbing nature of rubber, plus the fact that the rubber strip is wide and bulky, together with the fact that the blade of a snow-plow is generally set at an angle so as to deflect snow to the roadside, whereby the impact of the blade does not occur all at once, combine to make the rumble strips as described very easy to plow.

Although not called for by present standards, the rubber strips may be of a bright, even fluorescent, colour, to further alert a driver to the hazard. It may be noted that the colouring would be inherent in the rubber, and would not be worn away. The fact that the upper surface of the rubber strip protrudes serves also to make the strips easily visible, especially in dark, wet conditions, when any road marking that does not protrude can be almost invisible.

Although the upper surfaces of the rubber strips have been shown as convex in the drawings, it is within the scope of the invention that the strips may be flat on top, and may be set flush with the road surface. This would reduce the rumble intensity, and the visibility, but would render the strip even less liable to plowing problems, such as might arise for example in very cold conditions when rubber loses some of its flexibility.

The upper surface of the rubber strips may be provided with a series of grooves. These would assist in conducting water away from the surface, and would provide a measure of skid resistance.

It may be noted that in the rumble strips as described some small interval of time will elapse from the moment a tire strikes the rubber until the rubber starts to descend, due to the hysteresis of the material. This delay would be totally insignificant if the strip were narrow, but, because the strip is some centimetres wide, in the invention, the delay is sufficient that the rubber does not sink so quickly when the tire passes at a rapid speed, as when the tire passes slowly.

Therefore, a characteristic of the wide strip of the invention is that a rapidly travelling vehicle makes a louder noise than a slow vehicle, simply because the rubber cannot move aside very quickly. It is known that it is effective to place rumble strips progressively closer together, the nearer to the hazard, to make it appear to the driver that he is going too fast: even more so with the invention, the vigour and intensity of the rumble alarm signal as created by a fast vehicle is considerably greater than that created by a slow vehicle.

It is contemplated, in the invention, that the rubber strip might alternatively be pre-set in a channel, the channel being made of metal or hard plastic. The attachment of the rubber to the material of the channel could then be carried out in the factory. The securing of the channel into the groove of course would still have to be carried out in situ, but it is a less demanding task to produce, on the road, a good secure bond between the channel and the groove, than between the rubber and the groove. However, the provision of a channel would normally be required -only if the material of the road were particularly soft, or in other adverse conditions.

In the rumble strip as described, the process by which the groove is cut involves traversing the cutting head along the length of the groove. The reflex-percussion process produces a groove in which the walls and base are very accurately defined, with strong edges; and in particular, the junction between the walls and the base is accurately defined. This means that the rubber component may be made to fit very intimately into the wall-to-base junction or corner. The result of this intimate corner-fit is that the strip has a great resistance to rotation of the rubber about an axis parallel to the length of the groove. The groove is disposed across the width of the roadway, which means that this high resistance applies to the mode of rotation in which the rubber might work itself out of the groove, due to the long-term action of traffic.

Thus, in the invention, it is recognized that by using reflex-percussion the rubber can be made to fit very intimately into the corners between the walls and the base of the groove, and that therefore the rubber will have a great tendency not to rotate itself out of the groove. It is recognised that this resistance is utilized, in the case of a rumble strip running across the road, because the direction of the traffic is transverse to, and not parallel to, the direction of traverse of the cutting hammer.

It may be noted that the the rumble strip as described above is intended to extend across nearly the full width of a traffic lane, ie to be of about 3 metres in length. It is contemplated, however, that the strip may be shorter, and sometimes may be much shorter. Such a short strip might be hardly longer than its width, and it should be understood that the term rumble strip as used herein includes within its scope such a short rumble strip, which may rather be described as a rumble stud.

A rumble stud could be used as a between-lanes marker or delineator. As mentioned, it is important that the direction of traverse of the reflex-percussion hammer should lie transversly across the roadway, and not lie along the length of the roadway, and therefore the rumble stud should be so oriented that the (short) groove is cut transversely across the width of the road, and not parallel to the length of the road.

Reflex-percussion is not an appropriate process for cutting straight down, ie for drilling holes, or cutting a recess straight down, without a lateral traverse, into a body of concrete or asphalt, where the profile of the recess is the same as the outline of the cutter. Reflex-percussion comes into its own only when the cutting head is traversed in a direction parallel to the plane of the surface into which the recess is being made.When cutting straight down, ie without traverse, the recess would tend to become clogged with debris -- this may be contrasted with the process of drilling such a recess, in which the drill-bit is provided with flutes for clearing the debris; Thus, in reflex-percussion it is preferred that the cutter be traversed across the surface in order to cut the recess: in the invention, it is preferred that the direction of traverse should lie transverse to the length of the roadway; and it is important that these preferences be applied also in the case when the rumble strip is a rumble stud.

Preferably, therefore, the rumble stud takes the form of a short rubber strip inserted into a short reflex-percussion groove, where the groove was cut by an across-the-road traverse. In this case, the stud may be very secure, and is able to stand up to years of service, including snow-plow action, without the rubber tending to work out of the groove due to repeated traffic contact.

It might be considered that the rumble stud could be set in a groove which is cut by a reflex-percussion traverse that is directed not across, but along the length of, the roadway. But in such a case, the resulting rumble stud would be much less secure, and that orientation of the strip is not preferred, in the invention.

Claims (9)

1. CLAIM 1. A procedure for providing rumble strips in a

   roadway, comprising the steps: of providing a reflex percussion apparatus, having at least one piston and an associated hammer, which are arranged for rapid vibratory movement towards and away from the surface of the roadway so as to strike blows at a rapid rate on the surface of the roadway, wherein the apparatus includes a piston retraction means, operated by compressed air, for forcibly retracting the hammer clear of the road surface, substantially at the instant a blow has been struck; of cutting several grooves in parallel, laterally across the width of a traffic lane of the roadway, at the approach to a hazard, wherein each said groove is several centimetres wide; of providing strips of elastomeric material, one per groove, wherein each strip is of a width such that the strip is a tight fit in its respective groove; of providing a means for constraining the strips securely against working loose from their respective grooves; and of inserting and sealing the strips in their respective grooves.
2. CLAIM 2. Procedure of claim 1, wherein the apparatus includes a means for constraining the hammer against rotation.
3. CLAIM 3. Procedure of claim 2, wherein the hammer is provided with a plurality of cutting bits in the form of bars, which extend across the width of the groove.
4. CLAIM 4. Procedure of claim 3, wherein the bars of one piton extend across only a portion of the full width of the groove, and of providing and arranging sufficient additional pistons in the apparatus that the bars in aggregate straddle the full width of the groove.
5. CLAIM 5. Procedure of claim 4, including the step of cutting the full width of the groove in a single pass of the reflex-percussion apparatus.
6. CLAIM 6. Procedure of claim 1, wherein the strip of elastomeric material substantially completely fills the groove, and protrudes slightly above the road surface.
7. CLAIM 7. Procedure of claim 1, wherein the strip of elastomeric material is of constant cross-sectional profile along its length, and wherein the strip includes a void or hole within the profile.
8. CLAIM 8. Procedure of claim 1, including the further steps: of providing an anchor strip, having a profile with an enlarged upper form, of providing fixing means for fixing the anchor strip securely within the groove; of providing a form in the profile of the elastomeric strip that is complementary to the form in the profile of the anchor strip; and of assembling the elastomeric strip lengthwise onto the anchor strip.
9. CLAIM 9. Procedure of claim 8, including the further steps of cutting a channel in the base of the groove, and of fixing the anchor strip in the channel.