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                        The Benefits of Pavement Markings: A Renewed Perspective Based on Recent and Ongoing Research


            
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                EFFECT OF PAVEMENT MARKINGS ON VEHICLE OPERATIONS
Measures such as speed and lateral position in the travel lane are surrogate measures for safety that are commonly used in the absence of crash data. The following subsections describe recent research that relates to the effect of pavement markings on lateral position and speed.

**Vehicle Speed**
While there have been a number of studies that used vehicle speed as a measure of pavement marking performance, most show no significant effect in absolute speed difference or, perhaps more importantly, speed variance (which is strongly correlated with crash rates [*30, 31*]). For instance, in 2004 van Driel et al. (*32*) performed a meta-analysis of vehicle operating speeds based on edge line presence. The range of reported before-after results was –3 mph (reduction in mean speed) to +8.1 mph. An overall increase in mean speed after installing edge lines on roadways that previously only had a centerline was less than 0.5 mph. The authors came to the conclusion that the net speed effect was essentially zero.

In 2005, researchers from Louisiana reported on a before-after study of adding edge lines to narrow two-lane highways (with pavement widths of 20 to 22 feet) (*33*). Conclusively, the researchers found that the addition of an edge line on narrow two-lane highways did not impact vehicle speeds, day or night.

A recent study performed by Donnell et al. (*34*) for FHWA focused on the effectiveness of pavement marking delineation on curves to induce consistency in vehicle speed and lateral position based on a nighttime driving experiment. Based on the results of the present nighttime driving experiment, the use of brighter or wider pavement markings does not improve speed consistency between an approach tangent and the midpoint of a horizontal curve.

Tsyganov et al. (*35*) conducted a before-after study on rural two-lane highways where edge line markings were added. The highways had lane widths of 9, 10, and 11 feet. The researchers discovered that there were no significant differences in vehicle speeds before and after adding edge lines to the narrow highways. They also learned that there were no statistical differences in vehicle speeds when considering daytime versus nighttime conditions. The researchers’ findings consistently showed that speeds slightly increased in all conditions after edge lines were applied, but the differences were not deemed statistically significant. They also showed that their absolute speed standard deviations were all less than 1 mph.

Many experts believe that drivers reduce speeds based solely upon their perceived risk. For instance, if drivers perceive sharp curves, narrow lanes or shoulders, steep roadside drop-offs, low side friction, etc., they will lower their speeds accordingly.

**Lateral Vehicle Position**
While research shows that the variance of vehicle lateral placement is strongly correlated with crash rates, there have been inconsistent findings related to the effect of pavement markings (*36, 37*). A meta-analysis of lateral vehicle position was performed by van Driel et al. (*32*). Based on research conducted in the United States, the change in mean lateral position after installing edge lines on roadways that previously only had a centerline was approximately 0.5 inches toward the centerline. The range of reported before-after results was a –10.5-inch shift (toward the centerline) to a +14-inch shift away from the centerline. The authors came to the conclusion that the net lane position effect was essentially zero.

The work previously described by Donnell et al. (*34*) resulted in findings that indicate there is little evidence to show that enhanced pavement markings change the way in which motorists transition from a tangent into a curve. As such, the authors concluded that use of enhanced pavement markings does not improve driver lane position differential between an approach tangent and the midpoint of a horizontal curve.

On the other hand, Cottrell (*38*) compared the lateral vehicle position of vehicles using 4- and 8-inch-wide edge lines. The results indicated that lateral vehicle position variance was unchanged at locations with a 4-inch edge line but was lowered during both day and night for the 8-inch edge line condition.

The research conducted in Louisiana also investigated lateral placement as a function of adding edge lines to rural two-lane highways (*33*). Their before-after measurements show that edge lines help drivers confine their traveling path, particularly at night. They found that with edge lines, centralization of vehicles’ position is more apparent at nighttime and drivers generally position their vehicle away from the edge line, irrespective of the roadway alignment.

Tsyganov et al. (*35*) also evaluated lateral placement after adding edge lines to narrow two-lane highways. They discovered a reduction in vehicle lateral placement variability, meaning vehicles were more consistently following a specific path. The exact location of that path depended on the overall lane width. For the 9-foot lane width, the vehicle path shifted closer to the newly installed edge line, especially in the curve sections. For 10-foot lane widths, there were no consistent changes noted. However, for the 11-foot lane width highways, the majority of the drivers moved closer to the centerline, especially on the curve sections. However, all the changes were subtle.
      
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                Book:The Benefits of Pavement Markings: A Renewed Perspective Based on Recent and Ongoing Research
              ABSTRACT
                INTRODUCTION
                ANNUAL PAVEMENT MARKING EXPENDITURES
                BENEFITS OF PAVEMENT MARKINGS
                PAVEMENT MARKING SAFETY STUDIES
                SUBJECTIVE EVALUATIONS
                EFFECT OF PAVEMENT MARKINGS ON VEHICLE OPERATIONS
                MEASURES OF PAVEMENT MARKING VISIBILITY
                OTHER PAVEMENT MARKING STUDIES
                FINDINGS
                DISCUSSION
                REFERENCES U.S. DEPARTMENT OF TRANSPORTATION

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