In pursuit of unimpeded high peak traffic flow, the "Design Guidelines for Super Two Highways" (Ekem, 1998) suggested several treatments for the right side of the roadway. But the left side is where drivers experience great speed differentials between their own vehicles and oncoming traffic. The authors examined centerline treatments and possible recommendations for Super Two guidelines. The current US standard (12-ft lane/4-in. dashes) was compared with combinations of wider lanes, wider dashes, and buffer areas. With each of the centerline treatments examined, participants kept the left side of the vehicle in the approximate center of the lane. All treatments resulted in shifting the center of the lane farther from the centerline than it was in the standard condition. Two conditions appear to be most effective in keeping drivers away from the centerline: 1) 14-ft lanes with both longitudinal rumble strips and 4-in.-wide dashes marking the centerline, and 2) 12-ft lanes with 4-ft buffer marked by 4-in.-wide dashes. However, implementing any of the centerline treatments should result in vehicles driving farther from the centerline, thus making it less likely that drivers will meet an oncoming vehicle. Data were gathered in a driving simulator. Further testing should be conducted in real driving situations.
