The approach is effective in slow-moving traffic , and it allows drivers to take advantage of the lane that is about to close. In less-dense, free-flowing traffic, there is less need to rely on the late merge, officials said.

A work zone engineer for the Kansas Department of Transportation, Kristi Ericksen, said in an email that officials would customarily expect in work zones to see “large differences in the speed of traffic (nearly at a standstill in one lane and highway speeds in the adjacent lane) and road rage (rude gestures, eliminating gaps, lane blocking).”

Since the late merge was introduced, the queues for those two types of lanes are about half the length officials expected, and drivers take turns at the merge point, she said.

“As for traffic flows, the data suggests that while the speeds are lower and the travel time may not be shorter, traffic continues to move and is predictable,” she wrote. “In other words, the travel conditions are more reliable, which has its own set of benefits.”

But when people apply their “off-road sensibilities” to their driving, the late merge can be harder to manage, Mr. Vanderbilt, the author, said in an interview last week.

For instance, a person would be considered rude if he or she walked to the head of a line of customers waiting for a bank teller. A driver in a free lane who zipped to the merge point and then tried to cut in could be judged similarly. Some drivers then take it upon themselves to become traffic monitors, enforcing societal norms and straddling the lanes to block those who might try to get ahead, he said.