For many drivers, it came out of nowhere.

A change to the layout of lanes between Leverett and Charles circles on westbound Storrow Drive in Boston last week confused and upset a number of drivers.

Many complained, state officials said, that the new pattern the state is testing out caused bottleneck traffic. The pattern forces motorists in the right lane to merge left, while turning the far left "exit-only" lane into a travel lane that lets drivers keep heading straight.

"I don't think that this has gone as smoothly as we had hoped," said state Highway Administrator Jonathan Gulliver. "I mean, certainly, it was a well-intended change. [We] felt that adding that extra capacity that was going to improve the driver experience."

A graphic of the lane configuration the state is testing out on a section of westbound Storrow Drive in Boston. (Courtesy MassDOT)

And the "driver experience" in the affected area was well-known for gridlock; it's where drivers from Interstate 93, Route 1 and Route 1A converge. Traffic models informed the state's decision to conduct the lane experiment.

Still, the shifted pavement markings stretching across 800 feet of the Charles River-adjacent artery appeared to take some drivers by surprise — and, in some cases, even inspired outrage on social media.

State officials said in a statement Tuesday that it will consider "driver behavior" in weighing whether the new lines actually improves traffic flow.

Gulliver told WBUR that "getting people to break out of those [driving] habits that in some cases are decades-old is really important."

The new lane configuration will stay in place through next week, MassDOT officials said on Dec. 7.