While this paper includes some of the most common and often cited measures of pavement marking performance, it is not intended to be 100 percent comprehensive. Other techniques have been used successfully to evaluate pavement markings and measure their benefits. One approach is based on psycho-physiology measures that account for the workload of the driver. Another approach monitors drivers’ eye movements to identify how drivers use pavement markings during their driving tasks. Examples of each of these techniques are described below.
Driver Workload Measures
Tsyganov et al. (35) conducted a unique 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 tested driver workload before and after edge lines were installed. For workload, the researchers monitored heart rate. They found that the addition of edge lines on narrow two-lane highways decreased workload at nighttime conditions for both free driving conditions (i.e., no oncoming vehicles) and meetings with oncoming traffic. For instance, the addition of edge lines showed an average 15 percent decrease in the total time when participants were deemed to be experiencing high mental workload rates during nighttime driving conditions. On average, the mean nighttime mental workload rate was reduced by 12 percent after adding edge lines. Other means of measuring driver workload have been used in the past as well, including galvanic skin response, steering fluctuations, accelerator and brake pedal activations, etc.
Driver Eye-Tracking Measures
As described above, visibility-related research provides inconclusive results in terms of increased detection distances provided by wider markings. However, an ongoing safety study is demonstrating that wider markings can reduce crashes on rural two-lane highways.
Pavement markings provide two primary functions: previewing the roadway alignment (using far or foveal vision) and maintaining lane position (using near or peripheral vision). Foveal detection tasks have been thoroughly studied to no avail (i.e., inconsistent findings) in terms of identifying benefits of pavement marking width. Therefore, it seems reasonable to postulate that peripheral visibility measures may provide a stronger visibility measure of effectiveness in terms of identifying benefits of wider pavement markings. In fact, McKnight (54) conducted research showing that intermediate crash measures, such as lane positioning attention management (where drivers focus their attention), are related to peripheral vision. The researchers showed that major improvements in lane keeping are associated with wider pavement markings (studied under low contrast levels).
TxDOT is sponsoring research aimed at determining how wider pavement markings may assist the driver in lane keeping tasks by allowing the foveal focus (i.e., driver attention) to be available more often for other driving tasks because of the enhanced information available through peripheral vision. A hypothesis to be tested is that the peripheral vision system, at least when constrained to a particular boundary and known scene, such as the view through the windshield during nighttime driving, is capable of target recognition using very low cognitive power.
The premise is that a driver’s central vision, which is only directed to short-distance pavement marking viewing when needed (i.e., low-visibility conditions or unexpected targets), would be more available for other driving tasks such as scanning the roadside, reading signs, checking mirrors, etc. Undoubtedly, there are endless targets recognized in the periphery that somehow are processed as insignificant and therefore cause no need for our central vision focus. If wider markings can reduce the amount of time the central focus is needed on short-range pavement markings, then the potential benefits of wider markings could be realized. Drivers could then manage their foveal vision on other driving tasks as noted above, therefore ultimately providing a safer driving environment.
The research requires drivers to navigate a serpentine test track in an instrumented vehicle during nighttime conditions while wearing state-of-the-art eye-tracking equipment. In stage one, the drivers’ view is controlled so that they see the course under two conditions. The first condition is with their standard low-beam headlamps. The second condition is similar except that the near-field illumination is removed (i.e., occluded). Comparison of lateral placement, speed selection, and eye-tracking data will allow the researchers to test the strength of the premise regarding how drivers rely on pavement markings using peripheral vision.
Assuming this premise holds true and is validated through the testing described above, the researchers will repeat the experimental plan in three phases (stage two). The differences between each phase will be the pavement marking retroreflectivity and the pavement marking width. Using this approach, it is envisioned that the research could develop relationships demonstrating how the use of wider lines permits drivers to manage their vision system in a more effective manner, which would lead to a reduction in crashes. This research has the potential for a significant breakthrough in terms of quantifying the benefits of wider markings, particularly demonstrating how drivers use pavement markings at night to maintain their lane position.