More than a hundred flights have been canceled at Denver International Airport over the weekend, as airlines followed new federal orders to reduce air traffic across the nation.

While many major airlines have not released full lists of their canceled flights, United’s cancellations in Denver show many shorter routes have been impacted first.

The most affected airport connecting to Denver? Colorado Springs.

Of the 115 canceled United flights impacting Denver, 22 of them were connections to Colorado Springs.

Denver is home to the third-busiest airport in the nation, which is among the 40 airports required by the Federal Aviation Administration to reduce air traffic by 10%.

More than 70 flights were affected at DIA on Friday, according to FlightAware, an online tracker of air travel disruption, and more than 200 flights were delayed.

The Trump administration is requiring airports to reduce their air traffic as the longest government shutdown in U.S. history hits 38 days, saying the move is necessary to ensure safety. The shutdown has compounded the nation’s shortage of air traffic controllers, as federal workers have not received paychecks since the shutdown began.

Reductions started at 4% on Friday and will ramp up to 10% by Nov. 14, the FAA’s order said. It’s in effect from 6 a.m. to 10 p.m. local time and impacts all commercial airlines.

It’s not clear how long it could take to get back to normal, but the restrictions could worsen as U.S. Transportation Secretary Sean Duffy warned Friday that the FAA may reduce the number of flights up to 20% if the shutdown persists.

WHICH FLIGHTS HAVE BEEN IMPACTED THE MOST?

United Airlines, the largest operating airlines out of Denver International Airport, released a comprehensive list of its canceled flights from Friday to Sunday.

About 115 flights flying from or to Denver have been canceled as of Friday morning, according to United. It’s approximately 40 flights each day.

“This represents about 20 roundtrip flights a day in Denver, which are primarily United Express flights to destinations with multiple flights a day,” said Russell Carlton, an airline spokesperson.

The airline’s most impacted routes are often connecting to smaller airports in the West and Midwest.

No flights between Denver and the East Coast have been canceled this weekend yet, according to United’s list.

So far, United cut 22 flights to and from Colorado Springs Airport over the weekend. About 10 flights will affect Grand Junction Regional Airport and eight will affect Durango-La Plata County Airport.

In total, 35% of United’s canceled flights at DIA will impact other connections in Colorado.

The longest Denver routes impacted have been to Seattle; Portland, Ore.; Columbus, Ohio; and San Diego and Burbank, Calif.

United’s strategy is to keep all of its international flights and hub-to-hub connections running to “maintain the integrity of our network” and give passengers as many options as possible, the airline’s CEO, Scott Kirby, said in a staff memo Wednesday.

“Instead, we will focus our schedule reductions on regional flying and domestic mainline flights that do not travel between our hubs,” he added.

Delta also said it would not cut international flights.

United’s first impacted Denver flights to and from destinations outside of Colorado on Friday included Minneapolis, Minn.; Rapid City, S.D.; Santa Fe, N.M.; Albuquerque, N.M..; Seattle; Lincoln, Neb.; Portland, Ore.; Phoenix; Dallas, Texas; Amarillo, Texas; Salt Lake City, Utah; and Sacramento, Calif.

By Saturday, United expanded its cancellations to include Midland, Texas; Kansas City, Mo.; Omaha, Neb.; Casper, Wyo.; Billings, Mont.; and Wichita, Kan. Two flights to Aspen were also cut.

United’s Sunday cancellations add airports in Scottsbluff, Neb.; North Platte, Neb.; Columbus, Ohio; Las Vegas, Nev.; San Diego, Calif.; Austin, Texas; and Burbank, Calif.

United still expects to have about 4,000 flights each day, the airline said its on website. Because its early November, the airline added they should have more flights available with open seats compared to the summer.

Southwest Airlines did not respond to a request for comment and specifics on DIA’s impacts. The airline is giving customers flexibility to rebook flights between Nov. 7 and Nov. 12, according to its website.

Frontier Airlines, which is based in Denver, also did not respond to a request for comment.

It posted Thursday night that cancellations for Friday and Saturday are set. Frontier is working on finalizing cancellations from Nov. 9 and onward. It will update customers when more information becomes available.

Though other airlines haven’t shared full lists of their cancellations, FlightAware shows the most impacted airports with Denver flights on Friday include L.A., Phoenix and Colorado Springs.

WORRIES AND POTENTIAL FOR SURGE IN ALTERNATIVES

Travelers are worried.

Benjamin Sanderson, donning a blue beanie and armed with a camera while taking photos around Union Station on Friday morning, is concerned about how he would get home to Houston after visiting Denver.

He said he had planned to fly home Saturday, but didn’t know yet if he’d be able to.

“I haven’t heard anything yet about my flight. I guess I’ll know when I check in tonight,” Sanderson said.

Regarding a backup plan in case his flight got canceled or delayed, he said he’d come up with one, as needed.

“I start a new job back home on Monday and they don’t know I’m here,” Sanderson said. “I’ve got to get home before then.”

Flight cancellations could lead to a surge in alternative travel options, such as rental cars and trains.

Historically, rental car companies see a demand surge during widespread flight delays and cancellations. This week’s cancellations could cause rental car prices to jump, as many companies have dynamic pricing models.

Hertz has already seen a spike in one-way rentals by more than 20% compared to the same weekend last year, said Emily Spencer, a spokesperson for the rental car company.

Spencer added that the spike is understandable when considering that many of the canceled air routes are “drivable.”

“We join the airlines in urging Congress to swiftly pass a clean continuing resolution and restore certainty for travelers,” Hertz CEO Gil West said in a statement. “Every day of delay creates unnecessary disruption. We are grateful to Secretary Duffy, who we know is working hard to bring leaders together to end the shutdown.” 

Spencer has a few extra tips for car renters this week, notably booking through a neighborhood location to avoid airport complications and adding flight information to the car rental reservation. 

“Our locations actively monitor flight delays and cancellations, and adding your flight information can help protect your reservation,” she said.

Amtrak — which runs daily trains from Denver to Salt Lake City, San Francisco and Chicago through its California Zephyr train — also wants travelers to know its open for business.

“Amtrak is operating full service and is ready to welcome travelers with a smooth, flexible, and convenient experience,” an Amtrak spokesperson said. “As air travel becomes less reliable, more riders are choosing the convenience of rail — a trend that began before the government shutdown and any flight cancellations.”

Staff writers Deborah Grigsby and Michael Braithwaite contributed to this report.