Adding stop lines at two-way stop-controlled intersections doesn’t directly correlate to improved safety, according to U of M researchers. Stop lines are frequently used along with regulatory stop signs to indicate where drivers must stop before they enter the conflicting traffic lane, but very little research had been conducted on this pavement marking’s effect.
“The benefits of stop lines had been assumed, not proven,” says John Hourdos, director of the U’s Minnesota Traffic Observatory. “And while one stop line is not an expensive addition, maintaining them at hundreds of intersections can become a sizable expense for local agencies.”
The safety study’s key finding was that the presence of a stop line showed no association with crash occurrence when used as the sole predictor. A field study showed that in all cases—both before and after stop line installations—drivers stopped 10 feet or more after the stop sign or stop line.
Additionally, researchers found that the more space there was between the line or sign and the edge of the conflicting driving lane, the more drivers ignored the stop line. After stop lines were added, some cases showed drivers stopping even closer to the conflicting lane than before.
On a more positive note, although the presence of the line did not increase the number of drivers that come to a full stop, overall rolling stops became slower rolling stops, Hourdos says. Researchers concluded that while the marking has some effect, most frequently it is not the predicted one—and in some cases not even the desired one.
The study provides welcome insight at local public agencies such as the City of Edina, which maintains stop lines at 700 intersections. “By no longer installing and maintaining stop lines, agencies can allocate more funding elsewhere for proven safety improvements,” says Nick Baler, Edina’s traffic safety coordinator.
The research was sponsored by the LRRB.
—Megan Tsai, CTS freelancer