There's construction everywhere at the Minneapolis-St. Paul International Airport — both inside and outside the main terminal — and now it's spread to where passengers least like to be held up: the security checkpoint.

On Tuesday, the airport closed the general lanes at the south security checkpoint in Terminal 1 as crews began installing four "innovation lanes" that in the long run could speed up screening by up to 40 percent.

But for at least the next three weeks, all passengers who are not part of trusted traveler programs will have to pass through the north security checkpoint. Two lanes at the south checkpoint will remain open, but only for passengers with TSA Precheck or Clear.

"Chalk it up to the pain of progress," said airport spokesman Patrick Hogan.

Over the past year, inbound and outbound roads have been torn up, escalators have been taken out and temporary walls have gone up throughout the terminal as the Metropolitan Airports Commission has embarked on $1.6 billion in improvements.

The latest disruption comes as automated screening lanes are added. During installation and testing, there will be four fewer lanes available to screen passengers and some extra long walks from the baggage drop to the gate.

Traveler Linda LaCroix, who was heading back to Arizona after visiting her parents in Eagan, shrugged in disappointment after she checked in with Delta and tried to use the adjacent south checkpoint Tuesday morning. She was directed to the other end of the terminal.

"My flight probably is leaving from this end," she said as she made the trek down the corridor. "I hate when you have to wait [at the checkpoint] because it can get really long."

A few passengers looked panicked when Delta agent Bashir Waged sent them to the north checkpoint. Others were sanguine, like Jon Ramold of South Carolina, who considered it more steps on his Fitbit.

Though signs at the south checkpoint read "TSA Precheck Check Only," "People have no idea what is happening here," Waged said as he sent hundreds the other way. "I just say I'm sorry."

The new system will allow as many as five passengers at a time to place their bags on a conveyor belt.

Each station will have a bin dispenser so travelers can fill bins without waiting as long for a spot. The loaded bins with radio-frequency chips on them will then move on roller belts into X-ray inspection as passengers head to their own screening. After inspection, bags and bins that pass screening will roll down one conveyor belt uninterrupted while those deemed to need a second look will be pushed out to the side.

Rules for what has to come out of carry-on luggage have not changed, so many passengers will need multiple bins. Laptops, for example, will still need a separate bin. The average traveler at MSP uses about four bins, according to David McMahon, the TSA's deputy federal security director for Minnesota.

"You can walk around those who are slower divesting," McMahon said. "This will be a more efficient movement of property going through and a good enhancement of security."

Another feature is that the system automatically returns bins to the passenger station. That means TSA agents won't have to collect bins, stack them up and wheel them through the metal detector on their way back to the beginning of the line. That task can slow down screening, McMahon said.

But just how fast passengers get though security will depend on how quickly they adapt to the system.

"There will be a learning curve," McMahon said.

Delta Air Lines, the airport's dominant carrier, requested that the lanes be added to the south checkpoint. The Metropolitan Airports Commission is spending $1.6 million to put in the new lanes. Hogan said the airport plans to add them at the north checkpoint next year.

The MAC opened the new 10-lane north checkpoint and consolidated several checkpoints into two in February 2016. Now, 18 months later, the airport is giving checkpoints another upgrade. McMahon said MSP didn't put the innovation lanes in at that time "because they were not available."

Automated security lanes debuted last spring at Atlanta's Hartsfield-Jackson airport. Since then, innovation lanes have been installed at Chicago O'Hare, along with Miami, Los Angeles, Dallas-Fort Worth, Newark, N.J., and Phoenix. McMahon called them the "wave of the future."

On Tuesday, passenger volume was light as crews started assembling the system of belts and rollers. Late August tends to see fewer travelers because the peak summer vacation time has passed, and the next big crush won't occur until October, when schools are out across the state for a long weekend as part of Minnesota Educator Academy training, Hogan said.

Last year September was one of the airport's slower months, with just over 3 million passengers boarding or arriving at MSP.

Still, airport officials strongly advised passengers to arrive two hours early for domestic flights and three hours before departure for international flights.

Tim Harlow • 612-673-7768