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Visibility of Lane Markings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-2 Effectiveness of Symbolic Markings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-4 Markings for Pedestrian and Bicyclist Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-6 Post-Mounted Delineators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-8 Markings for Roundabouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-10 20-1 C H A P T E R 20 Markings
VISIBILITY OF LANE MARKINGS Introduction Visibility of lane markings refers to the ease with which drivers can see and follow longitudinal lane markings. Lane markings are designed for a certain preview time, the amount of time that drivers look ahead on the roadway. This preview time is affected by the distance at which drivers can see markings, which is a function of retroreflectivity and marking width. Different lane marking patterns and colors can have different meanings and regulate different driver actions, such as exiting, lane changing, passing, and maintaining roadway position. For this and other safety reasons, it is important that drivers are able to see and understand lane markings from an appropriate distance. Design Guidelines Factor Guideline Preview Time Absolute minimum preview time = 3 s Recommended preview time = 5 s Marking-Specific Luminance Minimum Dark Luminance = 100 mcd/m2/lux Minimum (adjusted for dirt) Dark Luminance = 121 mcd/m2/lux Marking Width If there is concern about the visibility of the markings, use a 6 or 8 in. marking width instead of the standard 4 in. mcd = millicandela Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data MATHEMATICAL ESTIMATION OF VISIBILITY DISTANCE BASED UPON MARKING RETROREFLECTIVITY AND WIDTH (1) (MODELS ARE FOR YOUNG DRIVERS AND DO NOT CONSIDER GLARE) Visibility distance (D) for longitudinal road markings in high-beam illumination Visibility distance (D) for a continuous road marking of 10 cm width in uniform illumination (simulated daylight) Where: RL is the coefficient of retroreflected luminance (and RL (road) = 15 mcd/m 2/lux) RL (mcd/m 2/lux) Luminous intensity is constant towards the road markings (10,000 cd) Where: C is the contrast ratio between the pavement marking and the roadway L is the luminance in cd/m2 (Note: Road surface luminance levels in Europe typically range from 0.5 to 2 cd/m2.) HFG MARKINGS Version 2.0 20-2
Discussion Preview time: There is some disagreement regarding the minimum amount of preview time that should be provided for drivers. Rumar and Marsh (2) determined through a literature review that a 5-s preview time accommodates proper anticipatory steering behavior, safe steering on roads that are not straight, and the minimum long-range preview time. However, the same review revealed that the Commission Internationale de lâEclairage (CIE) recommended a lower bound of 3 s for preview time. Schnell and Zwahlen (3) suggest adding an 85th percentile eye-fixation duration of 0.65 s to the 3-s minimum chosen by the CIE to account for the time required for the driver to see and process the marking information. This value is also supported by the COST study, which found that drivers initially had a 2.18-s average preview time, but when the visibility of road markings in the on-road study was increased, the preview times increased to 3.15 s on average (1). Additionally, drivers increased their speed very little to compensate for the increased marking visibility (equivalent to approximately 0.1 s of the time increase) and thus preserved the remainder of the preview time. Therefore, this recommendation is to provide a 5-s preview time when possible, but a 3-s preview time as an absolute minimum. Retroreflectivity: Pavement line retroreflectivity affects the distance from which drivers can view a pavement marking. In a study using subjective observer ratings, Graham, Harrold, and King (4) found that 85% of participants 60 years of age and older rated markings with retroreflectance values of 100 mcd/m2/lux or greater as being adequate or more than adequate when viewed under nighttime conditions. They also calculated a 21% increase in this value (to 121 mcd/m2/lux) to account for occluded light due to dirty windshields and headlights for vehicles that are reasonably maintained. Additionally, more than 90% of the young subjects rated a marking retroreflectance of 93 mcd/m2/lux as adequate or more than adequate for night conditions. In another study utilizing subjective ratings, Ethen and Woltman (5) also found 100 mcd/m2/lux to be the minimum for dark conditions. Note that the luminances that were rated as acceptable were much higher (300 to 400 mcd/m2/lux) in comparison to the minimum values (5). Marking width: The standard width for most longitudinal pavement markings is 4 in. In a survey of state highway agencies, 58% have used markings that are wider than the standard 4-in. marking for centerline, edge line, or lane line applications (6). The data are limited regarding the effectiveness of these markings. However, when surveyed, drivers placed high priority on the quality of pavement markings (6). A variety of studies have shown that when wider than standard pavement markings were used, mean lateral placement was more centered, fewer lane departures on curves were observed, and lanekeeping in low-contrast situations improved (6). Gates and Hawkins (6) concluded that these wider markings show benefits for locations where a higher degree of lane or roadway definition is needed, such as in horizontal curves, roadways with narrow or no shoulders, and construction work zones. Although many of these findings result from a test of one width (either 6 or 8 in.), Gibbons, McElheny, and Edwards (7) found that visibility distance increased for a 6-in. width, but not correspondingly for the 8-in. width. This finding suggests that there may be a threshold where performance does not significantly increase with an increase in line width. Design Issues Problems with glare are more pronounced with the elderly, because optical deficiencies of the eye increase with age. In addition to the temporal visual impairments, glare can cause discomfort and fatigue. In a simulator study with a 4-in. edge line and opposing headlamp glare conditions, subjects aged 65 to 80 required an increase in contrast of 20% to 30% over a younger sample to correctly discern downstream curve direction. To accommodate less capable drivers, the study suggests an increase in stripe brightness of 300% (8). Gates, Chrysler, and Hawkins (9) found that short-range driving performance, including activities such as lane positioning, is more reliant on driver peripheral vision than foveal vision. Wider markings are believed to provide a stronger signal to the driverâs peripheral vision over standard width markings, thereby improving driver comfort and short-range performance. Most studies about marking width involve long-range driving tasks such as end detection, which are performed by foveal vision. Cross References None. Key References 1. Commission Internationale de lâEclairage (1999). COST 331: Requirements for Horizontal Road Marking. Luxembourg: Office for Official Publications of the European Communities. Retrieved from ftp://ftp.cordis.europa.eu/pub/cost-transport/docs/331-en.pdf. 2. Rumar, K., and Marsh, D.K., II (1998). Lane Markings in Night Driving: A Review of Past Research and of Present Situation (UMTRI-98-50). Ann Arbor: University of Michigan Transportation Research Institute. 3. Schnell, T. and Zwahlen, H.T. (1999). Driver preview distances at night based on driver eye scanning recordings as a function of pavement marking retroreflectivities. Transportation Research Record, 1692, 129-141. 4. Graham, J.R., Harrold, J.K., and King, L.E. (1996). Pavement marking retroreflectivity requirements for older drivers. Transportation Research Record, 1529, 65-70. 5. Ethen, J.L., and Woltman, H.L. (1986). Minimum retroreflectance for nighttime visibility of pavement markings. Transportation Research Record, 1093, 43-47. 6. Gates, T., and Hawkins, H.G. (2002). The Use of Wider Longitudinal Pavement Markings (0024-1). College Station: Texas Transportation Institute. 7. Gibbons, R.B., McElheny, M.J., and Edwards, C.J. (2006). Impact of pavement marking width on visibility distance (06-1859.pdf). Proceedings of the Transportation Research Board 85th Annual Meeting [CD-ROM]. 8. FHWA (1997). Synthesis of Human Factors Research on Older Drivers and Highway Safety Volume 2 (FHWA RD-97-095). Retrieved from http://ntl.bts.gov/DOCS/97095/index.html. 9. Gates, T., Chrysler, S., and Hawkins, H.G. (2002). Innovative visibility-based measure of effectiveness from wider longitudinal pavement markings (VIS2002-30). Proceedings of the 16th Biennial Symposium on Visibility and Simulation . Retrieved from http://arrow.win.ecn.uiowa.edu/symposium/DraftPapers/VIS2002-30.pdf. HFG MARKINGS Version 2.0 20-3
EFFECTIVENESS OF SYMBOLIC MARKINGS Introduction Effectiveness of symbolic markings refers to the degree to which drivers follow and understand text or symbols on the roadway. A major component of pavement markings is horizontal signing, which is composed of sign text that is painted on the roadway. Horizontal signing is effective because drivers spend most of their time scanning the roadway in front of their vehicle near the horizon (1). Because drivers are already looking at the pavement, they are likely to see information there more quickly, preventing the need for an eye movement away from the road. Additionally, the pavement can be a good location to provide lane-specific information. Design Guidelines Marking Goal Do this: Do not do this: Reduce speeds in horizontal curves Curve arrow and â50 mphâ text âCurve 55 mphâ text Transverse lines âCurve Aheadâ text Reduce wrong-way movements on two-way frontage roads Lane direction arrows on a two-way frontage road by an off-ramp N/A Route shield in the exiting lane Route name text in the exiting lane Provide route guidance information for lane drops Pavement marking arrows (in addition to traditional lane drop markings) N/A Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data HFG MARKINGS Version 2.0 20-4
Discussion Speed reduction in horizontal curves : In an on-road study of horizontal signing to reduce speeds before horizontal curves, Chry sler and Schrock ( 1 ) found that the text âCurve 55 mphâ reduced speeds on a rural road by approximately 4 mi/h more than the control treatment. Although this finding was not statistically significant, the be nefit from this ma rking was greater than for the âCurve Aheadâ text (which did not cause a significant reductio n). When the curve arrow and â50 mphâ text were tested on an urban roadw ay, vehicles significantl y reduc ed their speeds by 10% at the entrance to the curve. There wa s also an 11% to 20% reduction in vehicles exceeding the speed limit. Note that the curve arrow and â50 mphâ text were tested in a section of the r oad following a vertical crest, so the arrow provided additional info rmation about the direction of the curve after drivers came over the crest. Another option if advisory speeds cannot be displayed is the text âSLOWâ w ith a curve arrow. Retting and Farmer ( 2 ) tested this marking on a suburban road and found that it significantly reduced the percentage of drivers exceeding the speed li mit by more than 5 mi/h during the daytime and late night time frames, but not during the evening. Overall, the markings that provided advisory speeds or an action performed most effectively. The results of transverse line treatments have been mixed. Chrysler and Schrock ( 1 ) found that a series of three pairs of transverse lines near the middle of the lane did not cause a significant speed reduction. However, Katz ( 3 ) found that transverse lines at the lane edges resulted in speed reductions, which were significant on interstate and arterial roadways, but not rural roadwa ys . Note that the treatments differed in multiple ways. Chrysler and Schrock ( 1 ) attempted to create a âvisual rumble strip,â which would appear in the driverâs foveal vision, on a rural road. Katz ( 3 ) used markings at the lane edges, which would appear in the driverâs peripheral field of view and create the illusion of higher than actual speed. Wrong-way movements on two-way frontage roads: Chrysler and Schrock ( 1 ) tested the implementation of lane direction arrows on a frontage road in Texas. The use of one-way and two-way frontage roads is widespread in Texas, potentially increasing the probability of wrong-way movements. Lane direction arrows were placed on the frontage road, 120 ft from the gore area of the exit onto the road. With the arrows installed, the rates of wrong-way driving maneuvers and conflicts were significantly redu c ed by 90% and almost 100% respectively. This overwhelming reduction in wrong-way drivi ng indicates that the treatment can have a beneficial safety influence on traffic at locations where drivers may be confused about appropriate lane selection. Lane drops: In a study of route guidance information regarding lane drops, Chry sler and Schrock ( 1 ) surveyed drivers about route markers. The majority (94%) of respondents preferred the route shield over the route name text. However, 29% to 48% of drivers thought that the marking indicated the route they were currently on rather than the upcoming exit. Therefore, route shields may be effective when used with other lane drop signs/markings. Fitzpatrick, Lance, and Lienau ( 4 ) tested another lane drop indicator: pavement marking arrows. With the addition of pavement marking arrows, erratic ma neuvers such as lane changes through the gore and attempted lane changes decreased. Drivers continuing on the main route moved out of the exit lan e earlier. Although these results were only significant for two out of the three sites tested, the other site had a lane drop on ly 1.6 km (1 mi) long, and vehicles may have shifted through the exit lane upstream of the study segment. Design Issues Horizontal signing has two issues that can be broadly applied: visibility of th e markings and durability of the materials on th e travel lane. Horizontal markings viewed during daytime must contrast with the road surface. White markings may not provide an adequate contrast for sy mbol recognition or word legibility when viewed against a concrete or worn asphalt surface. Conversely, nighttime visibility is affected by the durability of the optical elements presented in the marking material, typi c ally glass beads. Other visibility limitations can be found in shortened headways due to traffic congestion that may not be large enough for full horizontal sign viewing. Horizontal signs should have large simple components and should be visually unique to the highest possible degree. Proper application using text or sy mbols should minimize the use of abbreviations, keeping the sy mbols simple and legible. By limiting the application to critical locations, drivers will be able to recognize these signs a s an added warning or caution ( 5 ). Chry sler and Schrock ( 1 ) determined that when drivers are undergoing stressful driving conditions or situations where too much information is presented at one time, they will practice âload sheddingâ by ignoring the least important information and focus i ng on the more important tasks. Drivers will tend to look at the ro ad more and at side or overhead-mounted signing less when âloa d sheddingâ takes place. This behavior increases the importance of horizontal signing in the area where drivers look most. Cross References None. Key References 1. Chry sler, S., and Schrock, S. (2005). Field Evaluations and Driver Comprehension Studies of Horizontal Signing (FHWA/TX-05/0-4471-2). College Station: Texas Transportation Institute. 2. Retting, R.A., and Farm er, C.M. (1998). Us e of pave me nt ma rk ings to reduce excessive traffic speeds on hazardous curves . ITE Journal, 68 (9 ) , 30-34, 36. Retrieved from : http://www. ite. org/m em bersonly /itej our nal/pdf/JIA98A30.pdf. 3. Katz, B.J. (2004). Pavement Markings fo r Speed Re duction. McLean, VA: Turner-Fairbank Highway Research Center. Retrieved from : http://www.pooledfund. or g/docu me nts/TPF-5_065/speed_r eduction.pdf. 4. Fitzpatrick, K., Lance, M., and Lienau, T. (1995). Effects of pave me nt ma rkings on dr ive r behavior at freeway lane drop ex its . Transportation Research Record, 1495 , 17-27. 5. Chry sler, S., Sc hrock, S., and W illia ms , A. (2006). Research Recommendations for Pavement Marking Words and Symbol s . College Station: Texas Transportation Institute. HFG MARKINGS Version 2.0 20-5
MARKINGS FOR PEDESTRIAN AND BICYCLIST SAFETY Introduction Markings for pedestrian and bicyclist safety refers to pavement marking techniques to encourage safe practices for road sharing by vehicles, pedestrians, and bicycles. Pedestrian markings include crosswalks, which are defined as marked or unmarked extensions of sidewalks or shoulders across intersections (1). Crosswalks may also be located midblock, but only if marked. Bicycles and vehicles may utilize shared lanes on either rural or non-rural roadways. The purpose of markings in shared lanes is to notify users that the lane is shared and clearly define the positioning of the traffic flows. Design Guidelines RECOMMENDATIONS FOR INSTALLING MARKED CROSSWALKS AND OTHER PEDESTRIAN IMPROVEMENTS AT UNCONTROLLED LOCATIONS Vehicle ADT 9,000 Vehicle ADT > 9,000 to 12,000 Vehicle ADT > 12,000 to 15,000 Vehicle ADT > 15,000 Roadway Type (Number of travel lanes and median type) 30 mi/h 35 mi/h 40 mi/h 30 mi/h 35 mi/h 40 mi/h 30 mi/h 35 mi/h 40 mi/h 30 mi/h 35 mi/h 40 mi/h 2 lanes C C P C C P C C N C P N 3 lanes C C P C P P P P N P N N Multilane ( 4 lanes) with raised median C C P C P N P P N N N N Multilane ( 4 lanes) without raised median C P N P P N N N N N N N C: Candidate site for marked crosswalk. Marked crosswalk can be considered after an engineering study and confirmation of 20 pedestrian (or 15 elderly/child) crossings per peak hour. P: Possible increase in pedestrian crash risk may occur if crosswalks are added without other crossing improvements; locations should be monitored and enhanced with other improvements if necessary before adding a crosswalk. N: Marked crosswalks should not be added alone because pedestrian crash risk may increase; treatments such as traffic calming measures, traffic signals with pedestrian signals, or other crossing safety improvements should be considered. Source: adapted from Zeeger et al. (1) PLACEMENT OF RECOMMENDED SHARED-USE LANE SYMBOL FOR BICYCLISTS AND VEHICLES Source: Birk, Khan, Moore, and Lerch (2) Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data Approximate Parked Passenger Vehicle Width from Curb: 7 0 Approximate Open Door Width Centerline of Marking to Door Recommendations: Place the centerline of the shared-use arrow 11 ft from the curb. Use the bike-and-chevron symbol to denote a shared-use lane. Placement of shared-use arrow from curb. HFG MARKINGS Version 2.0 20-6
Discussion Crosswalks: Zeeger et al. (1) provide guidelines for the locations where marked crosswalks should be installed based upon a study of pedestrian crashes at marked and unmarked crosswalks. The guidelines apply to uncontrolled locations excluding school crossings. Crosswalks should not be installed in locations where additional pedestrian safety risks exist (e.g., poor sight distance, confusing designs) without other design features or traffic control devices (1). Crosswalks alone do not make crossings safer or guarantee that more vehicles will stop for pedestrians. Nowakowski (3) found that there are three critical locations where potential vehicular-pedestrian conflict could occur: the mid- block crossing and the left and right turning lanes at an intersection. The difficulty for the driver is detecting pedestrians because visual scanning and attention are limited. It is recommended that parking be eliminated on the approach to uncontrolled crosswalks to improve vision between pedestrians and drivers. The Uniform Vehicle Code (4) specifies that parking should be prohibited within 20 ft of a crosswalk at an intersection (which could be increased to 30 to 50 ft in advance of a crosswalk on a high-speed road). Design of the shared-use arrow: Shared-use arrows (also referred to as âsharrowsâ) on roadways attempt to reduce safety problems such as âdooring,â where bicyclists ride into parked vehicle doors when ajar; wrong-side riding; sidewalk riding; motorists squeezing out bicyclists; and other aggressive behaviors (2). Shared pavement markings can increase the percentage of bicyclists riding in the street, which can help reduce crashes with turning vehicles. Two bicyclist surveys and an on-road study regarding a number of shared-lane markings were conducted in San Francisco (2, 5). The lane markings tested were bike-and-chevron (shown on the previous page), bike-in-arrow (bicyclist inside of an arrow outline), and a separated bike-and-arrow. During the on-road study, the bike-and-chevron marking significantly reduced sidewalk riding (by 35%) and wrong-way riding (by 80%). It also increased all distances between moving cars, cyclists, and parked cars. Overall, 60% of cyclists thought that the markings positively affected their sense of safety and preferred the bike- and-chevron marking by a 2:1 ratio. However, 30% of cyclists indicated that the markings tested meant that bikes have priority, rather than that the lane is shared. The distance of the shared-use arrow from the curb is based upon parked vehicle width. Birk et al. (2) observed that the 85th percentile of car doors open 9 ft 6 in. from the curb, the average bicycle width is 2 ft, and 6 in. of âshy distanceâ is added between the open door and bicycle handlebars. In total, these distances indicate that the centerline of the pavement marking should be 11 ft from the curb. Design Issues Crosswalk lighting: In-roadway crosswalk warning lights can provide pedestrian safety benefits. With in-roadway warning lights: passing vehicle speeds decreased from 7% to 44% (6, 7), the percentage of drivers yielding to pedestrians increased during day and night by 26% to 162% (8, 9), and the percentage of drivers who saw the crosswalk, saw a pedestrian, and accurately stated the presence of the pedestrian increased by 13%, 25%, and 38%, respectively (8). Shared lanes: Shared-use lanes often exist where there is too little space available to create a dedicated bicycle lane. When space is available, a bicycle lane or wide curb lane may be created; however, there is disagreement as to which is better. See Hunter, Stewart, Stutts, Huany, and Pein (10) for a discussion of each lane type. Cross References None. Key References 1. Zeeger, C.V., Stewart, J.R., Huang, H.M., Lagerwey, P.A., Feaganes, J., and Campbell, B.J. (2005). Safety Effects of Marked Versus Unmarked Crosswalks at Uncontrolled Locations, Final Report and Recommended Guidelines (HRT-04-100). McLean, VA: FHWA. Retrieved from http://www.tfhrc.gov/safety/pubs/04100/04100.pdf. 2. Birk, M., Khan, A., Moore, I., and Lerch, D. (2004). San Francisco's shared lane pavement markings: improving bicycle safety. (Prepared for San Francisco Department of Parking and Traffic). Alta Planning + Design. Retrieved June 3, 2008 from http://www.sccrtc.org/bikes/SF-SharedLaneMarkingReport-Feb04- FINAL.pdf. 3. Nowakowski, C. (2005). Pedestrian warning human factors considerations. Retrieved from http://path.berkeley.edu/~cychan/Research_and_Presentation/Pedestrian_Detection_TO5200/Crosswalk_ HF.pdf. 4. National Committee on Uniform Traffic Laws and Ordinances (1992). Uniform Vehicle Code: 2000. Evanston, IL. 5. Center for Education and Research in Safety (2002). Report on human factors comparison on perceived meaning of three alternative shared use symbols (Submitted to The City of San Francisco). Retrieved from http://members.cox.net/ncutcdbtc/sls/cerssf02.pdf. 6. Dougald, L. (2004). Development of Guidelines for Installation of Marked Crosswalks (VTRC 05-R18). Charlottesville: Virginia Transportation Research Council. 7. Whitlock & Weinberger Transportation (1998). An Evaluation Of A Crosswalk Warning System Utilizing In-Pavement Flashing Lights [Executive Summary]. Retrieved from http://www.spotdevices.com/docs/studies/EvaluationCrosswalkWarningSystemUtilizingInPavementLights.pdf. 8. Katz, Okitsu & Associates. (2000). Illuminated crosswalks: An evaluation study and policy recommendations (Prepared for the City of Fountain Valley, California). Tustin, CA. Retrieved from http://www.xwalk.com/images/advocacy/ftnvlly_study.pdf. 9. California Department of Transportation. (2004). MUTCD 2003 California Supplement, Part 4: Highway Traffic Signals, Section 4L.02 In-Roadway Warning Lights at Crosswalks. Sacramento. Retrieved from http://www.dot.ca.gov/hq/traffops/signtech/mutcdsupp/supplement.htm. 10. Hunter, W.W., Stewart, J.R., Stutts, J.C., Huany, H.H., and Pein, W.E. (1998). A Comparative Analysis of Bicycle Lanes versus Wide Curb Lanes: Final Repor t. (FHWA-RD-99-034). McLean, VA: FHWA. HFG MARKINGS Version 2.0 20-7
P OST -M OUNTED D ELINEATOR S Introduction Post-mounted delineators (PMDs) are a type of retroreflective marking device mounted above the roadway surface and along the side of the roadway in a series to indicate the alignment of the roadway. Delineators are particularly useful at locations where the alignment might be confusing or unexpected, such as at lane reduction transitions and/or curves (1). They are also useful at night and during adverse weather. Delineators may be used on long sections of highways or on short sections where there are changes in horizontal alignment. An important advantage of delineators is that they remain visible when the roadway is wet or snow covered. Design Guidelines Spacing: Drivers respond similarly to fixed and variable spacing of delineators when perceiving curvature. Thus, either spacing method can be used for outlining the curve approach and departure segments. MUTCD (1) RECOMMENDATIONS FOR DELINEATOR SPACING ON CURVES Radius of Curve (ft) 50 115 180 250 300 400 500 600 700 800 900 1000 Approximate Spacing (S) on Curve (ft) 20 25 35 40 50 55 65 70 75 80 85 90 VARIABLE AND FIXED SPACING FOR CURVE APPROACHES AND DEPARTURES 2S 3S 6S VARIABLE SPACING (1)2S 2S 2S FIXED SPACING (2)SS S S Preview Times Post-mounted delineators should be visible with a preview time of at least 5 s. Number of Reflectors There is no difference in curve perception between single and double delineators; thus, either is acceptable for curve delineation. Color Drivers are not aware of the varying meanings of differently colored delineators. If differently colored delineators are used, drivers should receive education as to their specific meanings. Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data HFG MARKINGS Version 2.0 20-8
Discussion Spacing: Charlton ( 3) found that driversâ perceptions of speed and curvature appear to work at both a conscious (explicit) and unconscious (implicit) level. For this reason, curve warnings and delineation treatments that highlight the sharpness of the curve ahead or increase a driversâ mo mentary sense of their apparent speed appear to offer prom ise in allowing drivers to enter curves at a lower speed. Delineation treatments may also assist drivers with selecting and maintaining appropriate lane position while travelling throughout the curve. Chrysler, Carlson, and Williams ( 2) found that drivers cannot distinguish between fixed and variable delineator spacing on the approaches to horizontal curves. The two types of spacing led to functionally equivalent curve perceptions. Thus, Chrysler et al. ( 2) recommend that the approach and departure delineator spacings be fixed at two times the appropriate curve spacing found in the MUTCD. This recommendation can save installation time without sacrificing safety. More specific inform ation on spacing on horizontal curves can be found in the MUTCD. Preview time: Rumar and Marsh ( 4) explained two complementary road guidance functions: short-range and long - range guidance. Long-range guidance (over 5 s of preview ti me ) allows the driver to consciously predict the path of the roadway far in advance, drive sm oothly, and avoid time-pressure situations. Rumar and Marsh (4) found that preview ti me s provided by lane ma rkings alone are well under a safety criterion of 5 s and thus concluded that current lane ma rkings are not opti mal for safe night driving. Good & Baxter (5) found the addition of PMDs tends to have a positive effect for long-range guidance, but have no effect on short-range guidance. To be usable for long - range guidance, PMDs should be visible at a preview ti me of at least 5 s (about 440 ft at 60 m i/h (140 m at 100 km /h)) under low-beam illu mi nation. Number of reflectors: Chrysler et al. ( 2) found that the perception of curvature is not affected by the num ber of reflectors on the delineator. However, the co mb ination of one reflector and variable spacing leading up to the curve caused the perception of less curvature. Overall, Chrysler et al. ( 2) recommend that the MUTCD elim inate the distinction be tween th e two types of delineators and define a standard delineator. Larger delineators could still be used for em phasis where necessary. Color: Chrysler et al. ( 2) found that drivers do not understand the difference in placement for yellow and white delineators. Although respo ns e accuracy was poor for curve delineator color, when given a forced-choice question regarding crossover delineation, mo st drivers could recognize the correct color. This finding led to the recomm endation of putting mo re em phasis on delineator color in driver education courses rather than altering the MUTCD. Design Issues Another use of delineators is to define the roadway leading up to a railroad grade crossing. At rural crossings without active warning devices, the lighting may be poor and drivers may be more reliant on auditory train signals to know if a train is approaching. Howe ver, these auditory signals may not be co mp letely effective for drivers who are hearing im paired. Staplin, Lococo, Byington, and Harkey (6) found that approximately 30% to 35% of people aged 65 to 75 have a hearing loss, increasing to 40% for persons over the age of 75. The use of post-m ounted delineators would help highlight to hearing-im paired drivers that railroad crossing is imminent. Cross References None. Key References 1. FHWA (2009). Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). Washington, DC. 2. Chrysler, S.T., Carlson, P.J., and Williams, A.A. (2005). Simplifying delineator applications for horizontal curves. Transportation Research Record, 1918, 68-75. 3. Charlton, S.G. (2007). The role of attention in horizontal curves: a comparison of advance warning, delineator, and road marking treatments. Accident Analysis & Prevention, 39(5), 873-885. 4. Rumar, K., and Marsh, D.K., II (1998). Lane Markings in Night Driving: A Review of Past Research and of the Present Situation. (UMTRI- 98-50). Ann Arbor: University of Michigan Transportation Research Institute. 5. Good, M.C., and Baxter, G.L. (1985). Evaluation of Short-Range Roadway Delineation (Internal Report No. AIR 381-1). Melbourne: Australian Research Board. 6. Staplin, L., Lococo, K., Byington, S., and Harkey, D. (May 2001). Guidelines and Recommendations to Accommodate Older Drivers and Pedestrians (FHWA-RD-01-051). McLean, VA: FHWA. HFG MARKINGS Version 2.0 20-9
MARKINGS FOR ROUNDABOUTS Introduction Markings for roundabouts refers to pavement markings on the entrances to and exits from roundabout intersections. Roundabout intersections are defined by the MUTCD (1) as âcircular intersections with yield control at entry, which permits a vehicle on the circulatory roadway to proceed, and with deflection of the approaching vehicle counter- clockwise around a central island.â Roundabout markings need to display clear information to incoming drivers to ensure the safe circulation of vehicles. Conflict points occur where one vehicle path crosses, merges, or diverges with or queues behind the path of another vehicle, pedestrian, or bicycle. Within roundabouts, fewer conflict points occur as compared to conventional intersections; hazardous conflicts such as right-angle and left-turn head-on crashes are eliminated. Single-lane approach roundabouts provide greater safety benefits than multilane approaches because there are fewer potential conflicts between road users, and pedestrian crossings are shorter. Robinson et al. (2) note that lower vehicle speeds entering and in the roundabout provide drivers more time to deal with potential conflicts. Design Guidelines Luminance contrast between the curb markings and the pavement should be: 2.0 or higher for roundabouts with overhead lighting 3.0 or higher for roundabouts without overhead lighting Lum Luminance contrast = Lstripe â Lpavement Lpavement inance contrast is calculated by: Where: Lstripe = the luminance of the pavement marking Lpavement = the luminance of the pavement RECOMMENDED ROUNDABOUT PAVEMENT MARKINGS 200 mm (8 in) solid white 200 mm (8 in) solid white White legend (optional) 600 mm à 3 m (24 in à 10 ft) Zebra crosswalk, 600 mm (24 in) spacing (typical) 200 mm (8 in) solid yellow, 5 m (20 ft) spacing 200 mm (8 in) solid yellow 300 mm (12 in) broken white 1 m (3 ft) stripe, 1 m (3 ft) gap White legend (optional) 200 mm (8 in) broken white 200 mm (8 in) solid white Source: adapted from Robinson et al. (2) Based Primarily on Expert Judgment Based Equally on Expert Judgment and Empirical Data Based Primarily on Empirical Data HFG MARKINGS Version 2.0 20-10
Discussion Luminance contrast: Staplin, Lococo, Byington, and Harkey (3) recommended that retroreflective markings should be applied to the sides and tops of the curbs on the splitter islands and the central island. The recommended curb contrast levels refer to the contrast between these markings and the pavement. For roundabouts with overhead lighting, a contrast of 2.0 or higher was recommended. For roundabouts without overhead lighting, a contrast of 3.0 or higher was recommended. Staplin et al. (3) state that the luminance measurements should be taken at night, using low-beam headlamp illumination from a passenger vehicle, at a 5-s preview distance upstream of the intersection. Recommended roundabout pavement markings: The pavement markings in the figure shown on the previous page are from Roundabouts: An Informational Guide (2) and differ slightly from those included in the MUTCD (1). Several markings are usually placed within roundabouts to help regulate the flow and speeds of oncoming vehicles. Such markings include broken white lines, solid white lines, solid yellow lines, crosswalk markings, and roadway marking text âYieldâ. Roundabout lane markings follow the logic that yellow lines denote opposing traffic and white lines denote traffic moving in the same direction. A solid white line marks the right edge of the road. Additionally, normal or fish-hook lane-use arrow pavement markings may be used on roundabout approaches as defined by the MUTCD (1). A fundamental difference between roundabouts and traditional intersections is the continuous flow of traffic at roundabouts vs. the alternating of opposing traffic flows at traditional intersections (2). This difference creates different visual demands at roundabouts, where the driver is not given the right-of-way by traffic signals. Also, pedestrians are not given signaled time to cross roundabouts. The placement of crosswalks at roundabouts is further back in order to move pedestrians out of the continuous traffic flow. This placement also reduces the visual demands for drivers who otherwise would be required to look for approaching vehicles from the left and pedestrians from the right as they entered the roundabout. With the crosswalk further from the circular area, pedestrians cross in the driversâ forward field of vision (2). Crosswalks: It is important that the crosswalks preceding the roundabout have a high degree of visibility because they are set back from the yield line. Zebra crossings are recommended because they are highly visible, distinguish the intersection from signalized intersections, and are less likely to be confused with the yield line than transverse crosswalks (2). Bicycle lanes: The MUTCD (1) states that bicycle lane markings shall not be included within the circulatory roadway of a roundabout. The figure on the previous page shows how Robinson et al. (2) suggest that bicycle lanes should be included on an approach to a roundabout. This design provides a curb ramp where the bicycle lane ends to allow bicyclists to transition as a pedestrian to the sidewalk. Robinson et al. (2) state that, at roundabouts, bicyclists can circulate with other vehicles, travel as a pedestrian on the sidewalk, or use a separate shared-use facility for pedestrians and bicyclists where provided. Design Issues Stopping sight distance: Stopping sight distance should be provided at every point within a roundabout and on each entrance and exit (2). On the approach to the roundabout, vehicles need to have a stopping sight distance to the crosswalk and the yield line. When circulating, vehicles need to be able to see that same distance around the circle. When exiting the roundabout, vehicles need a stopping sight distance to the crosswalk. The intersection sight distance is the distance that a driver without the right-of-way needs in order to see and react to conflicting vehicles before entering the roundabout (2). Because of the geometry of the roundabout, the intersection sight distance implies drivers must look over/through part of the central island. This requirement poses restrictions on the height and placement of objects and landscaping in that island; appropriate sight distance requires a clear central island. However, Robinson et al. (2) recommends that only the minimum intersection sight distance should be provided because excessive sight distance can lead to higher vehicle speeds, reducing safety for all users. Cross References None. Key References 1. FHWA (2009). Manual on Uniform Traffic Control Devices for Streets and Highways. Washington, DC. 2. Robinson, B.W., Rodegerdts, L., Scaraborough, W., Kittelson, W., Troutbeck, R., Brilon, W., et al. (2000). Roundabouts: An Informational Guide (FHWA -RD-00-067). McLean, VA: FHWA. 3. Staplin, L., Lococo, K.H., Byington, S., and Harkey, D. (2001). Guidelines and Recommendations to Accommodate Older Drivers and Pedestrians (FHWA-RD-01-051). McLean, VA: FHWA. HFG MARKINGS Version 2.0 20-11
