Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SHEET MATERIAL MARJ~R SVRFACE FOR
~OADWAYS AND THE LI~E
Ihe present invention relates to the
distinctive marking of the directions of travel
on motoring highways, airports and other surfaces,
with the aid of thin marker strips adhered to the
traveling or other surfaces and embodying successive
spaced wedges provided with retroreflective materials~
the invention being more particularly concerned with
improved marker strips for such purposes.
Because of the extremely shallow angle
that is made between an automobile headlamp and
the roadway it illuminates, only a very small per-
centage of the light is reflected back for use by
the motorist. The problem is made even more severe
by the fact that the road surface is usually quite
flat with poor reflection characteristics, black
asphalt being the worst road surface from thia
viewpoint. Average road surface visibility with
low beams for the automobile headlamps at night is
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usually restricted to about 100 feet. Considerable
improvement is made by painting a white stripe on
the road surface~ but even this, with a freshly
painted line, does not extend road surface visi-
bility much beyond a couple of hundred feet. When
the road surface is wet with rain, moreover, the
visibility is drastically reduced even with a
freshly painted line and does not extend more
than a few tens of feet. The thin film of water
which covers the road and paint surface acts like
a mirror which reflects nearly all of the auto-
mobile headlamps' li8ht away from the motorist.
Thus, during rainy weather at night, even though
provided with a good white stripe, the road appears
almost pitch black to the motorist--this being the
ma~or reason why night driving in the rain is so
treacherous.
The art has concluded that the only
practical way to overcome this poor visibility is
by means of raised pavement markers which liter-
all~ ext~nd above the thin film of uater and
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retroreflect light back to the motorist. While
commonly used in certain regions of the nation,
especially in sunny climates, they are seldom
used in the snow regions because of the destructive
effects of snowplows. Efforts have been made to
ovércome this difficulty by designing a protectlve
framework or ramp which literally guides the snow-
plow blade up and over the marker with little
damageT but the general inability of some of these
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mar~ers to withstand the harsh treatment given
by the snowplows has prevented the1r widespread
adoption. Such special constructions, furthermore,
are expensive and are therefore usually positioned
quite far apart. In addition they are useful only
at night when illuminated by automobile headlamps
and are poorly visible, if at ali, by the motoring
public during daylight hours, often requiring an
additional or supplemental marker in the form of
a painted line or a plastic line for daytime drivin~ ,
gu1danoe.
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-- The art has struggled for years, however,
with a wide assortment of raised pavement ~arkers, -
of one configuration or another, for the ma~or
purpose of guiding the night-driving motorist.
The majority of these devices have little if any
detectability or utility durin~ daylight hours
and are thus confined to night-time conditions
wherein the illumination from automobile headl~mps
is redirected by means of internal reflection
back upon itself, thereby to be observed by the
operator of the vehicle. These devices often take
the form of buttons or mounds containing retro-
reflecting elements or surfaces. More recently,
ramp-like configurations have been adopted in
order to provide less hazard to the vehicles
traveling over them, some devices, indeed, having ¦-
special ramps, previously mentiohed~ to assist
in guiding the blades of snowplows, hopefully
without uprooting them. Such devices, as before
explained, are costly and, of necessity, must be
relatively widely spaced from one another along
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the roadway surface, resulting in the disadvantage
that, under headlamp illumination at night, al-
though bright in appearance, these devices at best
present only pinpoints of li~ht and not a con-
tinuous and highly desirable solid line, nor even
a semblance of a skip line. During dayli~ht con-
ditions they are usually not observable at all
by the motoring public at any distance.
In an effort to overcome some of the ¦
above and other disadvantages of such and related
raised pavement markers, markers of relatively ¦
low profile have been proposed, such as those
disclosed in U. S. Letters Patent Nos. 3,785,719,
4,035,059 and 4,279,471~ These concepts, however,
involved individual units which are still costly
to manufacture and thus again must be used with i
relatively wide spacing between units to achieve
realistic operational and cost effectiveness.
A more suitable approach for obviating
these problems has resided in the use of thin
flex.ble shee-ine on which ls contalned a ser1es
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of very low profile raised pavement markers as
described, for example, in my earlier U. S.
Letters Patent ~os. 3,920,346: 4,040,760s and
4,069,787~ and in Patent Nos. 4,145,112~
4,182,548; and 4,236,788. With the exception
of the constructions of my said Patent Nos. .
4,040,760 and 4,069,787, such sheet markers are
dependent upon having the main body of the marker
constructed so as to be transparent to light,
rendering the devices subject to serious light ¦ -
loss effects in use, caused by abrasion and ¦ -
accumulated dirt. In my said earlier construc- j
tions, embodying the use of somewhat saw-tooth
successive wed~es carried by a thin road-attachable
strip, while quite satisfactory operation can be
attained, it has been found that shadow effects
when heading into the sun, and modification of
results after the wedges have experienced some
wear, as from extended use and/or snowplow de-
facement or the like, do not permit as effective
marking in daylight, dusk or under other adverse
conditions as may be desirable.
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In the case of the successive wedges -
of substantially trian~ular shape taught in my
said Patent No. 4,040,760, for example, extended
use revealed that under certain conditions of
ambient daylight, the pavement marker became
somewhat difficult for the motorist to observe.
In particular, if the ~arker strip is oriented
in such a way that the motorist is heading in
the general direction of the sun on a cloudless !
day, the contrast between the marker and the road
surface is so low that the marker becomes diffi- ¦
cult to distinguish. During these conditions, ¦
the sun will cast a shadow of each wedge on the
valley floor between the wedges. Those faces of
the wedges observed bythe motorist~ furthermore,
are all contained within the shadow and thus appear ¦
black, introducing great difficulty in distinguish-
ing the marker from the dark road surface. Ihe
appearance of blackness or the poor contrast !
between the marker and the road surface is at a
peak when the sun is at a low angle on a cloudless
day.
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;. ~ It was fortuitously discovered that
- by changing the saw^tooth shape from triangular
to trapezoidal, but onl.y with appropriate wedge
length tO successive wedge spacing, this problem
was completely obviated, and simultaneous other
marked advantages in greater wear-resistance and
life under abrasion, including snowplowing, also
followed. The flat tops of the now trapezoidal-
shaped wedge, if of appropriate dimensions and
spacing, reflect sunlight and reduce the wedge
shadow effect admirably well.
An object of the present invention, accord-
ingly, is to provide a new and improved marker
structure that shall not be subject to the above
and other disadvantages, but that can obviate
shadow and discontinuous effects and provides a
marked improvement in wear and use under adverse
- environmental conditions.
An additional object of the invention
is to provide a flexible sheet material pavement
marker or the like which will be clearly visible ~'
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as à continuous line by ambient dayli~ht as well -
as retroreflection from automobile headlamps at
night, even during a heavy downpour of rain.
A further object is to provide a flex-
ible sheet material pavement marker with a con-
figuration and low profile sufficient to resist
uprooting by normal snowplow action.
Still another object is to provide a
highly visible highway marker for night driving
with a long life and with good retroreflection
characteristics maintained throughout such life.
A further ob~ect is to provide a novel
marker of more general utility, as well.
Other and further objects are explained
hereinafter and are more particularly pointed out
in the appended claims.
In summary, however, the invention, from
one of its aspects, contemplates in combination
with a roadway surface and the like, a direction-
indicating surface marker strip of-~+-S~R~
flexible plastic material adherable to said surtace
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by a thin layer of adhesive between the strip and the
surface, the strip being intermittently deformed upward
to provide successive transversely disposed wedges of sub-
stantially trapezoidal shape in longitudinal section, each
wedge having a substantially flat top surface bounded by
upwardly and downwardly acute-angle inclining front and
rear surfaces, the inclining surfaces being provided with
embedded retroreflecting beads. Preferred details of
construction and best mode embodiments are later set forth.
The invention will now be described with reference
to the accompanyin~ drawings, Fig. 1 of which is a
lonaitudinal sectional view of a preferred embodiment
of the invention; and
Fig. 2 is a similar view of a modification.
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Referring to Fi~. 1, the thin flexible
plastic elongated road marker strip 1 is shown
adhered by a bottom adhesive layer 4 to the road-
way or other surface K. Suitable materials are
described in my said earlier patents and are
hereinafter discussed. As previously described,
the somewhat saw-tooth wed~e construction i8
illustrated in the form of substantially trape-
zoidal (in longitudinal section) wedge pro~ections
T having a flat top surface 2 and bounded by up-
wardly and downwardly inclining front and rear
ridge sùrfaces 2' and 2", all extending trans-
versely across the strip 1, and all preferably
integrally formed from the thin plastic material
of the strip 1, with the wedges intermittently
deformed upward of the strip.
A preferred range of acute angles cC
of inclination (or downward slope) enable proper
operation in ~se as hereinafter discussed. At
least the upwardly and downwardly inclined sur-
faces 2' and 2" carry a retroreflective bead ~
layer( 9 ~ or the like 3. ~-
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ith this construction, it has been
discovered that, instead of observing an apparent
extension of a portion of one wedge face continu-
ously merging with the next succeeding wedge face
portion and so on, as described in my earlier ¦;
patents, in the case of the trapezoidal wed6e of ¦:
Fig. 1, there is an interruption in the apparent .
merging wedge faces by the width of the flat top
surface 2 of the trapezoidal wedge T. Considering
daylight operation, including heading into the . .
sun, when this diffusely reflecting flat top sur- :
face 2 has the same apparent area as that observable .
portion of the wedge face which is in shadow, it
has been found that the visual effect of the sun
shadow becomes sufficien~ly reduced to permit the
marker 1 to be readily visually distinguished from :
the road surface ~. This provides ~arker indica- ;
tion under such daylight or dusk considerations
that previous constructions do not adequately ';
provide. Increasing the area would provide even
better dayli~ht contra-t between the marker and ~'
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the road surface. but the apparent brightness
of night time retroreflection from automobile
headlamps would diminish. The condition for pro-
ducing apparent equal areas is fulfilled when
the width of the flat top surface 2 of the trape-
zoidal wedge T is made about equal (comparable)
to that of the valley floor 1' between successive
wedges. It has also been determined that, for
the purposes of the invention, the height of the
wedges is preferably a small fraction of the wedge
width (longitudinally); preferably of the order
of 1/6 or so.
Tests have shown the effectiveness of
such a construction for supplementing night-time
retroreflection with adequate daylight marker
observation even under shadowing conditions, for
the marker strip of Fig. 1 of the following speci-
fication~l
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Flat top surface (Z) w~dth 300 mils
Valley floor (1') width 300 mils
~idge hei~ht (vertical
height of 2', 2"~ 50 mils
Angle c~ ~ubstantially 0_45D
Glass beads (3) 5-10 mils diameter
(n=l.9)
When observed from a light source directed at an angl~
of about 85 from the normal, the light return by
retroreflection from surfaces 2' or 2" was ex-
cellent. As placed on a pavement surface R and
observed late in the afternoon on a cloudless sunny
day, with the marker strip 1 oriented so that heavy
shadows of the ridges 2', 2" were formed on the
valley floors 1' between the same, viewing at
angles of 45 to 85 from the normal in the general
direction of the sun, demonstrated that the marker
appeared clearly light in tone against the dark
road surface. In night time retroreflection, it
has been determined that a motorist at 1200 feet
distance should be able to view the top row of 10
mils beads on the wedge ridges.
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In Flg. 2, the provlsion Or retrorer1ect1On
beads 3 is shown over all surfaces of the marker strip
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A satisfactory technique for fabricating
the specially configured marker strips of the 1,
invention involves the use of a mold machined
out of, for example, an aluminum block, say 4 j
inches wide and 1/2 inch thick. The grooves for ~
the samples above described were 300 mils wide j
at the tops (corresponding to marker top surfaces 2)
with 30 sloping sides (corresponding to 2', 2n), ;¦
50 mils deep. Each groove was spaced 600 mils
apart. Narrow strips of 5 mil-thick polyethelene ¦;
were secured to the ~loping walls of the mold
grooves with a suitable heat-resistent adhesive 4.
The told was heated to about 280F and glass mlcro-
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spheres 3 (10 mils diameter, with a refractive
index n of about 1.9) were poured into the grooves
and pressed into the softened polyethelene. Af~er
cooling the mold, the e~cess microspheres were
removed so that the only ones remaining were those
immersed to approximately 4~/. of their diameters
in the polyethelene. Next, a plastisol of PVC
containing a white pig~ent was added to fill the
grooves of the mold and cover the top side to a
depth of about 15 mils. This was placed in a
heated oven for sufficient time to ensure bringing
the plastisol to a temperature of about 330F in
order to fuse and solidify the castin~. hThen
cooled, the PVC casting was stripped from the
mo~d with the microspheres now securely anchored
to about 60% of their diameters in the sloping
sides of the ridge or wed~e walls of the PVC cast- '
in~. ¦
Further modifications will sug~est them-
selves in the light of the above to those skilled in
this art, and such are considered to fall within the
spirit and scope of the invention as defined in
the appended claims.
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