Street closures, roadwork and congested airports around the New York metropolitan area may make travel this Labor Day weekend a challenge.

Sam Schwartz, the traffic expert and former city traffic commissioner credited for popularizing the term “gridlock,” said New Yorkers should expect “record traffic volumes” this weekend.

“Gas is down about 40 cents a gallon from last year and the airports are expecting record travel,” he said. “So there are certain times of day definitely to avoid. Thursday is the new Friday.”

Schwartz is recommending people start their travels before the afternoon, when travel times ramp up. He recommends leaving town before 11 a.m. on Thursday, or before noon on Friday. Too early? New Yorkers might also opt to leave around 7 p.m. on Friday, when most people have already left for their trips.

Here’s what to expect if you’ve got travel plans this weekend.

In the skies

A record-breaking 6.7 million travelers are expected to flood the city’s airports and vehicular crossings during the Labor Day travel period, which runs from Thursday through Tuesday, according to the Port Authority of New York and New Jersey.

An estimated 2.5 million travelers will use the JFK, Newark, LaGuardia and New York Stewart International airports. Thursday, Friday and Monday are expected to be the busiest during the six-day period, according to the same travel advisory.

“If you’re driving to the airports – don’t,” James Heitmann, the Port Authority’s chief operating officer, said during a press conference this week. “It’s really going to be a massive amount of traffic trying to get around. We put in a lot of mitigations but – if you need to drive – pre-book your parking in one of our parking garages.”

The Port Authority says domestic travelers should plan to get to airports two hours in advance, and international travelers should expect to arrive three hours in advance. Until next Sept. 4, the AirTrain JFK single-ride fare will be cut in half, to $4.25, to encourage travelers to use mass transit.

On the roads

Domestic road travel over Labor Day weekend is expected to increase by 9% compared to last year, according to projections from AAA released earlier this month.

And gas is down – drawing more people to the roads. Prices in New York are hovering around $3.50 per gallon on average this weekend compared to $3.90 this time last year, according to AAA.

New York is also the fourth-most popular Labor Day weekend destination for domestic travelers, behind Seattle, Orlando and Anchorage.

An estimated 4.2 million vehicles are expected to use the Port Authority’s bridges and tunnels over the weekend. The authority is suspending all repair and construction projects at its crossings from 5 a.m. Friday to 5 a.m. Tuesday.

Routine maintenance at MTA bridge and tunnel crossings will be suspended starting at 1 p.m. Thursday. Daytime scheduled maintenance requiring full lane closures will also be suspended from 1 p.m. Friday through 6 a.m. Tuesday.

But some key lane closures are still expected, according to the Port Authority:

The Holland Tunnel will have one eastbound lane closed from 11 p.m. Thursday through 5 a.m. Friday. The New Jersey-bound tube of the Holland Tunnel will be closed during the same time period, for Hurricane Sandy-related repairs.

One southbound right lane will be closed on the Bayonne Bridge on Thursday from 7 a.m. to 3:30 p.m..

City officials warn there are other partial and complete roadway closures — including several near and leading to the Billie Jean King Tennis Center in Flushing, The entire lengths of several roadways are subject to closures at the NYPD’s discretion until the U.S. Open wraps on Sept. 9: the Grand Central Parkway, Brooklyn-Queens Expressway, Cross Island Parkway, Long Island Expressway, Whitestone Expressway and Van Wyck Expressway. Several local roadways could be affected as well.

The MTA has a guide to getting to the U.S. Open on public transit and is urging drivers to stay off the roads.

And as with most weekends, there are lots of closures for street fairs and repair work. The Department of Transportation publishes a weekly rundown for the five boroughs.

On the bus

NYC buses will run on a regular weekend schedule Saturday and Sunday. On Labor Day, they’ll run on the Sunday schedule.

On Friday, most NJ Transit buses will run on their regular weekday schedule, with a full breakdown here. On Labor Day, Monday, most buses will run on the regular Saturday schedule.

NJ Transit’s 319 bus from New York to Atlantic City and to Cape May is also running on an enhanced holiday schedule from Friday through Monday.

On the subway

There will be no 2 train service between Manhattan and the Bronx this weekend. Free shuttle buses will be available.

Service on the 3 train will also remain suspended over the weekend, with the 2 and 4 trains making those stops in Brooklyn. Free shuttle buses will be available there, as well.

On Saturday and Sunday, the subway will run on a regular weekend schedule. On Monday, the subway will run on a Sunday schedule — with no service on the B, W and Z trains; no express ​6 or 7 trains; and no express F trains in Brooklyn.

On Monday, from 11 a.m. to 8 p.m., 2 and 3 trains will skip Eastern Parkway-Brooklyn Museum in both directions for the West Indian American Parade. The MTA is advising riders to use the nearby Grand Army Plaza or Franklin Avenue-Medgar Evers College stations instead.

On Monday, PATH trains will operate on a modified Saturday schedule.

On the rails

On both Saturday and Sunday, the Long Island Rail Road will operate on a Saturday schedule. On Monday, it’ll run on a weekend-holiday schedule, with Montauk Branch trains running on a Sunday schedule.

The 7:18 a.m. train from Montauk to Hunterspoint Ave – which normally runs on summer Mondays – will instead run on Tuesday for those commuters traveling back to New York after Labor Day weekend.

The Metro-North Railroad will have service on both the East and West of Hudson Lines adjusted during Labor Day weekend. For East of Hudson lines, extra trains will run on both Thursday and Friday.

On the Hudson and Harlem lines, Metro-North Railroad will also operate early-getaway trains on Friday, for those who want to get out of the city ahead of the rush.

More details about the LIRR and Metro-North adjustments, including to West of Hudson lines can be found here.

NJ Transit is offering a fare holiday for trains and buses through Sept. 2 as a thank-you — or apology — after a summer of brutal delays. The service’s regular, weekend and holiday schedules are here.