Yellow Pavement Markings with Yellow Nighttime Color

Transcription

1 TRANSPORTATION RESEARCH RECORD Yellow Pvement Mrkings with Yellow Nighttime Color GREGORY F. JACOBS AND NORBERT L. JOHNSON Humn observers were used to ssess the pprent nighttime color of rnge of pvement mrking products. A_ totl of 24 different mterils were viewed t night from n utomobile using low-bem illumintion with vehicle-to-trget distnces rnging from 2 to 3 m. The smples were viewed s isolted center lne lines with prllel white edge line in plce for ll viewings. Observers rted the color on scle of to 5 from white to yellow. The results showed significnt color differences between pvement mrking mterils. At shorter distnces, more of the mterils ppered yellow thn t longer distnces. At longer distnces observer rtings showed greter seprtion of color distinction between the mterils. Retroreflective color ws mesured t geometries corresponding to 2 nd 3 m. Brightness did not pper to correlte with color. Color mesurements for the different distnces lso showed the dependence of color on test conditions. Mesured colors with higher color sturtion were reported by observers to hve more yellow ppernce. Dytime nd nighttime color re not the sme. Some yellow pvement mrkings hving cceptble dytime color were whit in retroreflective color. Different "yellow" products cn hve vrymg nighttime color performnce. The fesibility of specifying nighttime color using instrumentl methods tht cn correlte with the humn visul experience is demonstrted. Seven color-norml humn observers (bsed on Ishihr test results) were used to ssess the pprent nighttime color of new unworn pvement mrking mterils with white nd yellow dytime colors. All of the viewers hd "norml" visul cuity nd were licensed drivers in the stte of Minnesot. Their ges were 27, 37, 38, 39, 48, 48, nd 5 yers. One viewer ws womn. A totl of 24 different pvement mrking mterils were viewed. Of these, five were white nd the rest were yellow in dytime color. Ech mrking ws pplied to luminum test pnels.2 cm thick,.52 min length, nd. Om in width. Leding edges of the test pn- els were msked with mtte finish blck tpe. Viewings were held in prking lot well fter drk on n overcst night. The pvement ws recently surfced blck sphlt. Viewers were seted in 989 Pontic Bonneville 4-door sedn with low-bem hedlmps illuminted. The lyout of the test re is indicted in Figure. Lne width for the viewing re ws pproximtely 4 m. Smples were presented s isolted center lines.52 m in length nd. m in width. A length of white pvement mrking 2 m in totl length ws present s right edge line beginning 9 m closer to the vehicle thn the test smple re nd continuing.5 m beyond it throughout the view- ing experiment s control reference. Vehicle-to-trget distnces were 2, 24, nd 3 m (one to three skip lengths in front of the vehicle). Before beginning the test, observers in the vehicle were llowed to view five different smples spnning the rnge of colors in the experiment from white to yellow for bout 3 sec to develop n ide of the rnge of colors they would see during the test. The white edge line control ws in full view during this lerning period. The view- ers were instructed tht they would be presented with n isolted..::n:..:g=-:.::o:.::r::.:_:p:.:e=:ri"-o--:do=:f:=::2:-:--to3-!se-c.-a-;-;;ft-:e-r-v-:-ie-w-:-in_g_t:--;-h-:e-s-:-m-:-_----- Yellow nd white pvement mrkings re commonly used on rodwys to disply trffic lnes. A yellow pvement mrking typiclly will hve different mening to n utomobile driver thn white pvement mrking. For exmple, in the United Sttes, yellow pvement mrking is used on rodwy to seprte trffic lnes where the trffic moves in opposite directions, wheres white pvement mrking is used to mrk the rodwy's border t the shoulder nd to seprte trffic lnes where the trffic moves in the sme direction (J,2). In mny prts of Europe yellow pvement mrkings re used to indicte construction workzones or potentilly hzrdous driving situtions. In view of these different functions, it is importnt tht yellow nd white pvement mrkings re discernible to utomobile drivers, prticulrly t nighttime when visibility is limited. With incresed regultion to eliminte the use of led-bsed pigments, the development of yellow trffic mrkings free of such "hzrdous" colornts hs received significnt effort. It hs been found tht control of the reflective brightness (3) nd nighttime color ( 4) in desirble rnges for yellow pvement mrkings using orgnic colornts is not trivil. With the vilbility of pvement mrking systems hving vrying reflective performnce, the question of the reflective color of --rod-surfce-mrkings-providing-sfe-nd-effective-guidnce-hs--ce':'n_:ter:::.:li..:n:.:e:.::m'..'.:'..::r_:ki:= remined undefined. A prt of this in-use ppernce vribility stems from the lck of meningful mesures of nighttime reflective color of pvement mrkings tht correlte with wht drivers see. Trffic Control Mterils Division, 3M Compny, 553-IA-Ol 3M Center, St. Pul, Minn The object of this work ws to compre pvement mrking mterils tht differ in their nighttime reflective performnce using humn observers nd lbortory test methods for the mesurement of nighttime color of retroreflective mterils. The observer's color rtings of rnge of mrkings t night were compred with color chrcteriztion obtined through photometric mesurements of the mrking mterils. FIELD OBSERVATION OF PAVEMENT MARKING COLOR pie they would be sked to rte the night color of the smple from to 5, with being white nd 5 being yellow. Ech viewer hd response form on which, fter mking color judgment, they cir- cled the rting number djcent to the smple number. They would then be presented with nother smple nd continue through the smple set until the test ws completed.

2 48 TRANSPORTATION RESEARCH RECORD 495 2m 4.., I 4 m f} m. r.;;c;;;;ffij - L Viewer position.5 m in vehicle m 4._l24m m FIGURE Night viewing experiment lyout. During the ctul field observtions, the test smples were presented to the viewers in the vehicle for the sme period of 2 to 3 sec. Twenty-two of the mterils were viewed twice nd two were viewed three times ech for ech of three vehicle-trget distnces. Smple viewing order ws rndomized. No smple ws viewed twice in row. The overll dt collection included,5 points [(22 X X 3) smples X 3 distnces X 7 observers]. Figure 2 shows set of histogrms of the distribution of observer night color rting responses for one of the yellow products, T, t ech of the three viewing distnces. Figure 3 shows similr dt set for white mrking mteril, A. Figure 4 shows observer night color rting dt for nother yellow mrking, X. It cn be seen tht the distribution of observer night color rting nd the effects of viewing distnce for smple X differ from the response for smple T shown in Figure 2. Figure 5 shows the men observer night color rtings for ech product t ech distnce. Smples A through E hd white dytime color, wheres smples F through X hd yellow dytime color. Tble presents the men observer color rting for ech mrking mteril t ech of the viewing distnces nd pooled stndrd devition for ech distnce. Significnt differences mong the mrking mterils were observed. Distnce hd n effect on the pprent night color of the pvement mrkings. At shorter distnces, more of the mterils ppered yellow thn t longer distnces. At longer distnces, there ws greter seprtion of color distinction between the mterils. Also, t longer distnces, yellow mterils were rted less yellow nd white mterils were rted less white thn t shorter distnces. No effect of position in the vehicle or of n individul viewer (of those with norml color vision) on pprent color could be determined in this experiment. DETERMINATION OF TEST GEOMETRY The lbortory test mesurement geometries were clculted to correspond with 2- nd 3-m viewing distnces from the Pontic Bonneville. The vehicle-observer-smple geometries were clculted Distnce (m) whitest Observer Color Rting 3 m 24 m 2 m j i» CJ 5 C" yellowest = FIGURE 2 Night color oft.

3 Distnce (m) whitest Observer Color Rting 3 m 24 m 2 ml s yellowest t' 2 Cl = 8 =" 4 2 FIGURE 3 Night color of A. Distnce (m) whitest Observer Color Rtio 3 m 24 m 2 m s s.c 4 td 3 = 2 yellowest FIGURE 4 Night color of X. 5 b.i) 4.!!. b.i) =.: i:i:: 3.. Q u dy white dy yellow 2. -.Q D g t II D.. 8 ".. o 3 24 m. A B C D E F G H J J K L M N P Q R S T U V W X II " Reflective Pvement Mrking Mteril.. I 2 m I FIGURE 5 Observer night color rting by mteril.

4 5 TRANSPORTATION RESEARCH RECORD 495 TABLE Observer Night Color Rtings of Pvement Mrking Products A through X Distnce From Vehicle to Mrking 2 m Dytime Product Observer Stndrd Color Color Devition Rting 24 m 3 m Observer Stndrd Observer Stndrd Color Devition Color Devition Rting Rting white A.4.3 white B.2.43 white c.2.43 white D white E.3.3 yellow F yellow G yellow H yellow I yellow J yellow K yellow L yellow M yellow N yellow yellow p yellow Q yellow R yellow s yellow T yellow u yellow v yellow w yellow x Pooled Stndrd Devition Color Rtings: = Whitest, 5 = Yellowest for ll observer positions t ech distnce. The in-vehicle coordinte system mesurements re found in Tble 2. On the bsis of mesurements of the vehicle nd driver position nd the sptil lyout of the viewing experiment, the ngles of illumintion nd observtion were clculted s indicted in Figure. The ngles corresponding to ech viewing condition re shown in Tble 3. For purposes of simplifiction of the geometries for color mesurements, two-dimensionl pproch ws used, ignoring the effects of presenttion nd orienttion ngle nd ssuming left hedlight illumintion nd viewing from the driver position of the vehicle. With these simplifictions, the geometry corresponding to viewing distnce of 2 m ws 87. degree entrnce ngle/.5- degree observtion ngle nd for 3 m, 89. degree entrnce ngle/.7 degree entrnce ngle. LABO RA TORY MEASUREMENT OF NIGHTTIME BRIGHTNESS OF PAVEMENT MARKINGS Assessment of the nighttime brightness in the lbortory is usully through mesurement of the coefficient of retroreftected luminnce, RL, using the test method described in ASTM D-4. This is lso described s the reltive method in CIE Publiction 54 (5). In this method the mesured quntities re the reflected light, m,, the incident light, m;, the distnce, d, nd the re of the test surfce, A. The coefficient of retroreftected luminnce is determined by the following eqution: The viewing ngle, v, is the ngle between the direction of observtion nd the specimen norml. TABLE2 In-Vehicle Coordinte System Mesurements for 989 Pontic Bonneville Four-Door Sedn x y z Left Hedlmp Right Hedlmp Viewer Viewer Viewer Viewer mesurements re reported in meters ()

5 Jcobs nd Johnson 5 Step. Mesure Reltive Spectrl Vlues of Incident Rdition. Monochromtor PMT Telescope d l I Projector Source Step 2. Mesure Reltive Spectrl Vlues of Reflected Rdition. Monochromtor PMT FIGURE color. Digrm of reltive method for mesurement of nighttime LABO RA TORY MEASUREMENT OF NIGHTTIME COLOR OF PAVEMENT MARKINGS Mesurement of the nighttime color (NTC) using the direct spectrl method (ASTM E 8-93) is similr to the procedure for mesurement of the coefficient of luminnce, RL, using the reltive method (5). However for NTC, telespectrordiometer is used nd the mesurements cn be mde with n unclibrted source. Figure 7 shows digrm of the NTC mesurement method. The spectrl distribution of the incident light ws mesured t -nm intervls. Then the spectrl distribution of the retroreflected light from pvement mrking mterils ws lso mesured t -nm intervls. Averges of multiple scns nd shortened mesurement distnce of m were required becuse of the reltively low level of energy vilble. Clcultion of the spectrl coefficient of luminous intensity s function of wvelength, 'A., ws s follows: where m, = the reflected spectrl vlue, m; = the incident spectrl vlue, nd d = the test distnce. (2) TABLE3 Clculted Observtion nd Entrnce Angles for Night Viewing Conditions for Leding nd Triling Ends of Test Smple Illuminted by Left nd Right Hedlmps Viewed from Ech Viewer Position t Ech Distnce Observtion Angle (deg) Entrnce Angle (deg) left right left right Distnce Viewer begin end begin end begin end begin end 2.2 m m m "begin" indictes the end of the test smple closest to the vehicle. "end" indictes the end of the test smple frthest wy from the vehicle

6 52 TRANSPORTATION RESEARCH RECORD 495 R D mticity digrm. Tble 4 presents chromticity coordintes of retroreflected light from Illuminnt A nd the coefficient of retroreflected luminnce, RL, t geometries corresponding to 2- nd 3-m viewing distnces for pvement mrkings rted for color in the night viewing experiment. CORRELATION OF VISUAL OBSERVATIONS WITH PHOTOMETRIC MEASUREMENTS FIGURE 7 For unit vectors E, I, R,D cos =E I cosf3=i R Clcultion of observtion ngle nd entrnce ngle. Clcultion of tristimulus vlues ws s follows: x = k L, S(A.)RI(A.)i(A.)dA. y = kf As (A.)RI(A.)y(A.)dA. z = K f As (A.)R (A.)z(A.)dA. These clcultions use the usul symbols of CIE Publiction 5.2 ( ) using Illuminnt A nd the 2 degree observer. PHOTOMETRIC DATA Figure 8 shows n exmple of the spectrl retroreflectnce curve of yellow pvement mrking (Smple V) with yellow nighttime color nd mrking (Smple A) with white nighttime color for test smples mesured t the 3-m geometry. The chromticity coordintes for the retroreflected light when this mteril is illuminted using stndrd Source A re x =.5, y =.447 for the yellow nd x. =.452, y =.43 for the white mrking. Illuminnt A flls t x =.448, y =.47 on the CIE 93 2 degree observer chro Wvelength (nm) -White A. I-YellowV FIGURE 8 Exmple of spectrl wvelength distribution of retroreftected light from white nd yellow pvement mrking. (3) (4) (5) 78 In Figure 9 the mesured vlues of RL of mrkings A through X re mpped onto the chromticity coordintes for the dt t 89. degree entrnce/.7 degree observtion ngles corresponding to viewing distnce of 3 m. The brightness of the pvement mrking mterils ppers to be independent of the reflective color of the stripe. Figure shows the observer night color rtings from the viewing experiment t 3 m mpped onto chromticity spce t 89. degree entrnce/o. 7 degree observtion ngles. There ppers to be correltion between the color rtings of the observers nd the mesured chromticities of retroreflected light from pvement mrkings. Mrkings with higher color sturtion, closer to the edge of chromticity spce, were rted to hve yellower ppernce thn white mrkings. Figure shows color vlue rtings from the viewing experiment t 2 m mpped onto chromticity spce t 87. degree entrnce/.5 degree observtion ngles. Agin it is pprent tht there is correltion between the rtings of the observers with mesured retroreflective chromticities. As noted erlier, viewing distnce hd n effect on the pprent color of the pvement mrkings, with more of the mterils ppering yellow t shorter distnces thn t longer distnces. Comprison of Figures nd shows mesurble color shift with viewing condition. Some pvement mrkings become more "wshed out" in visul ppernce t frther distnces. The chromticities of the reflected light of these mterils move closer to the chromticity of the illuminnt (i.e., they become more "white"). There were lso yellow mrking smples (dytime color) tht received rtings close to those of the white mterils, for exmple, mrking smples L nd Nt 3 m. From Figure 5 it cn be seen tht the observer color rtings of some of the yellow mrkings re essentilly the sme s those for the white mrkings, prticulrly t frther distnces. The chromticities of the light retroreflected from these smples re in fct close to the chromticity of the light source Illuminnt A. It is possible to hve mrkings with cceptble yellow dytime ppernce, yet hve nighttime retroreflected color similr to white mrkings. For perspective of the loction of the nighttime retroreflected colors of the mterils used in this study, the chromticities t the 3-m geometry found in Tble 4 re plotted in chromticity spce for the 93 2 degree observer long with Illuminnt A in Figure 2. Figure 3 indictes the sme dt plotted on the 97 CIE u', v' digrm. SUMMARY Humn observers were used to ssess the pprent nighttime color of rnge of pvement mrking products. A totl of 24 different mterils were viewed t night from n utomobile using low-bem illumintion with vehicle-to-trget distnces rnging from 2 to

7 TABLE4 Chromticity nd Coefficient of Retroreflected Luminnce of Pvement Mrking Products A through X Viewing Distnce for Mesurement Geometry 2 m 3 m Chromticity RL Chromticity RL Product x y (mcd/m 2 /lx) x y (mcd/m 2 /lx) Al A A A B Cl C D E F G H I I K L M N p Q RI R s Tl T T u v w x Nwnber designtion with product letter indictes multiple mesurements of tht smple. indictes tht mesurements of tht smple were not vilble. FIGURE 9 Brightness s function of chromticity t 3-m geometry.

8 54 TRANSPORTATION RESEARCH RECORD 495 tio : ro :: u <I> > <I> l/l 3. yellow y y FIGURE Observer night color rtings for 3-m viewing mpped on chromticity. 3 m. The smples were viewed s isolted center lne lines with prllel white edge line in plce for ll viewings. Observers rted the color on scle of to 5 from white to yellow. The results showed significnt color differences between pvement mrking mterils. At shorter distnces, more of the mterils ppered yellow thn t longer distnces. At longer distnces observer rtings showed greter seprtion of color distinction between the mterils. Retroreftective color ws mesured t geometries corresponding to 2- nd 3-m viewing conditions. Brightness did not pper to correlte with color. Color mesurements for the different distnces lso showed the dependence of color on test conditions. Mesured colors with higher-color sturtion were reported by observers to hve more yellow ppernce. CONCLUSIONS o.oo ;m::;;..i FIGURE 2 Retroreftective chromticity of pvement mrkings A through X t 2- nd 3-m geometries plotted on chromticity digrm using CIE 93 stndrd observer. visul experience. However, more effort will be required to mke such mesurements routine nd to define more precisely cceptble color zones. These retroreftective color requirements for pvement mrkings re subject to the sfety needs of the driving environment in question. x Dytime nd nighttime color re not the sme. Some pvement mrkings hving cceptble yellow dytime color were white in retroreftective color. Different "yellow" products cn hve vrying nighttime color performnce. This work demonstrtes the fesibility of specifying nighttime color using instrumentl methods tht cn correlte with the humn 5. yellow u s Q) > <I> Ill..Cl G FIGURE Observer night color rtings for 2-m viewing mpped on chromticity. y FIGURE 3 Retroreftective color of pvement mrkings A through X t 2- nd 3-m geometries plotted on CIE 97 u', v' digrm. u'

9 Jcobs nd Johnson 55 REFERENCES. Mnul on Uniform Trffic Control Devices for Streets nd Highwys. FHW A, U.S. Deprtment of Trnsporttion, 988, Section 3A-5, p. 3A Trffic Control Devices Hndbook. FHW A, U.S. Deprtment of Trnsporttion, 983, Section 3A-4, p Bnov, A. The Mrkets, This week's developments: Colornts nd pigments. Americn Pint & Cotings Journl, Vol. 77, No. 5, Oct. 9, 992, pp Wldron, D. Advnces in Retroreflectivity of Yellow Trffic Striping. Presented t 73rd Annul Meeting of the Trnsporttion Reserch Bord, Wshington, D.C., Jn Retroreflection, Definition nd Mesurement, CIE Publiction 54. Centrl Bureu of the CIE, A-33, Vienn, Colorimetry, 2nd ed. CIE Publiction 5.2. Centrl Bureu of the CIE, A-33, Vienn, 98. Publiction of this pper sponsored by Committee on Visibility.