Travelers are on all sorts of special missions during Thanksgiving week, and they don’t get much chance to practice for them.

With the help of many travelers over the past decade, we’ve assembled holiday travel guidance. But if there’s one tip that can cover most circumstances, it’s this: You’re probably not leaving enough time for the trip.

Pre-holiday questions and post-holiday assessments in recent years suggest that many people tend to cut their departures too close for comfort.

Big improvements in travel forecasts can help with planning. But it’s just as important to stay alert to changing conditions during a trip, build in plenty of buffer time to endure the delays and have a backup plan.

Getting to the airport

“We’re getting close to Thanksgiving weekend, and the when-should-I-leave-work-on-Wednesday question has arisen,” said a commenter during a Dr. Gridlock online discussion. This traveler needs to reach Reagan National Airport from College Park, Md., for a 5:40 p.m. flight Wednesday.

“Would leaving College Park at 3 p.m. be cutting it too close?” the traveler asked.

That is mighty tight timing for Thanksgiving eve.

“Historically, Thanksgiving has been the busiest weekend of the year to fly, and this year will be no different,” said Bob Pishue, who analyzes travel trends for the INRIX traffic service. “Travelers should plan on commute times to airports to be about double longer than normal.”

Worst drive times

During the chat, another traveler commented about plans to split a trip to New York into a Tuesday night drive, with a hotel stay, followed by a Wednesday morning drive into New York.

That might cut stress, but as you drive away from the Washington rush hour on a long-distance trip, consider that at some point you’re heading into somebody else’s rush hour.

INRIX looked at nationwide travel trends for Thanksgiving eves. Among the top 10 busiest urban areas, Washington was in the middle of the pack for extra slow travel, with New York taking top honors.

The INRIX data showed that Wednesday’s trip times in the D.C. area could average 20 percent longer overall, while during the peak of the getaway, about 4 p.m., they could be 38 percent longer than normal.

So it’s certainly a good idea to avoid Wednesday afternoon driving if possible. But the staff at the region’s Transportation Planning Board reviewed traffic data and found that the pre-Thanksgiving Monday and Tuesday afternoons also are challenging, as regular commuters mix with the early getaway traffic.

In fact, Tuesday from 5 to 6 p.m. had the lowest average travel speed on the interstates and other prime travel routes.

Drivers in the New York area Wednesday will probably find traffic 33 percent slower on average, according to INRIX. But earlier is better. The slowest travel times in recent years come at about 4 p.m., same as in Washington.

On the main driving routes to New York, keep in mind that Philadelphia also ranks in the INRIX top 10 for worst traffic on Thanksgiving eve. Wednesday’s travel times average 16 percent worse than normal. During the afternoon peak, it could be about 30 percent worse than normal.

Thanksgiving Day is a much better travel day, but don’t expect Thursday to be traffic-free. Plenty of people with trips of moderate range will wait to travel on the holiday.

Black Friday

Although Thanksgiving Day provides a brief respite, traffic heading for the busiest suburban malls on Black Friday increases travel time around them almost 90 percent, according to the INRIX national survey.

“For consumers who want to spend the least amount of time driving to the malls, your best bet is to leave before 11 a.m.,” Pishue said.

Navigation

The navigation apps that travelers recommend most often are WAZE and Google Maps. Adjust the settings to get the directions and real-time advisories by voice, so drivers can keep eyes on the road.

Virginia, Maryland and most other East Coast states are part of the 511 information system. Motorists can dial 511 from within the states and get up-to-date information on travel conditions.

Delaware isn’t part of that system but does provide traffic updates to travelers who tune their radios to WTMC (1380 AM). Delaware also has a Twitter feed with traffic updates: @DelawareDOT.

In range of New York, check all-news WCBS (880 AM) or WINS (1010 AM) for traffic reports every 10 minutes.

Here are suggestions for some of the most popular destinations in the region.

Northeast Corridor

Traditional route: Interstate 95 to I-295, across the Delaware Memorial Bridge to the New Jersey Turnpike to northern New Jersey and then to New York (about 227 miles), and perhaps beyond to New England. This route has many tolls and much traffic.

Alternative 1: Route 50 across the Chesapeake Bay Bridge, follow Route 301 to Route 896 (Churchtown Road/Boyds Corner Road) to Route 1 (toll) or Route 13. From there, drivers can reach I-295 and the Delaware Memorial Bridge, which connects with the New Jersey Turnpike north to the New York area. This route avoids the Delaware toll plaza and includes some nice Eastern Shore scenery. But Routes 1 and 13 can be congested near I-95 and I-295.


Alternative 2: Baltimore-Washington Parkway or I-95 to I-695 (Baltimore Beltway) around the west side of Baltimore to I-83 north to I-81 north, just east of Harrisburg, Pa. Follow I-81 north, then take I-78 east into New Jersey. There, drivers can take I-287 to I-80, picking up I-95 for the George Washington Bridge (toll eastbound), or continue north on I-287 to the New York State Thruway and take the Tappan Zee Bridge (toll eastbound).

Other drivers like to head west before heading northeast. They take I-270 westbound, then pick up Route 15 in Frederick, Md., and drive north toward Harrisburg, Pa., where they can link to I-81 and I-78.

Travel tips: Your Plan B may include one of these alternatives, but don’t think of them as undiscovered shortcuts. Sections of them can be crowded at peak holiday travel times.

In Wilmington, Del., I-495 serves as a bypass for drivers who want to avoid congestion on I-95 through the city.

In southern New Jersey, toll-free I-295 serves as an alternative to the New Jersey Turnpike.

Many tolling authorities have added all-electronic tolling. This will be the first Thanksgiving season for all-electronic toll collection at the Tappan Zee Bridge. If you don’t have an E-ZPass, a monitor will record an image of the license plate and the registered owner will get a bill in the mail.

South and west

Traditional routes: I-66 to I-81, then I-64 heading west or I-95 to points south.

Alternative 1: Avoid much of I-81 and part of I-66 by taking Route 29 south from Gainesville, Va., through Culpeper, Charlottesville and on to Lynchburg, where you can take Route 460 west to join I-81 at Roanoke. Picking up I-81 at this point avoids some of the worst pockets of congestion farther north and a lot of the truck traffic that can make the interstate so frightening. Routes 29 and 460 are good four-lane highways.


Alternative 2: Avoid I-66 by taking I-95 south to Route 3 west in Fredericksburg, Va. Take a left onto Route 20 toward Orange, Va. In Orange, turn left onto Route 15 to Gordonsville, Va. At the traffic circle in Gordonsville, go to Route 231. Turn right at the end of the road, and that will take you to I-64. Go west, and you will reach I-81.

This route is an option for drivers who have had it with I-66. It doesn’t get drivers around the congestion on I-95 south of the Capital Beltway. To avoid that, drivers to the east may prefer Route 301. But this way also can be slow at peak periods, particularly at the Gov. Harry W. Nice Memorial Bridge over the Potomac River.

Drivers to the west may want to use Route 28 to Routes 15 or 17. Route 17 is an option for reaching the Tidewater area of Virginia.

Travel tips: The Washington region’s most notorious stretch of holiday road is I-95 in Northern Virginia. Don’t look for any improvement this Thanksgiving at the point near Garrisonville Road in Stafford County where the 95 Express Lanes and the I-95 regular lanes merge. Construction is underway to ease that bottleneck, but it won’t be done until 2018.

If driving south in the express lanes at a peak period, watch for electronic signs warning of congestion ahead and consider exiting those toll lanes.

Air and rail travel

For air travelers, the Friday, Tuesday and Wednesday before Thanksgiving and the Sunday and Monday after the holiday are traditionally the busiest at area airports. The Metropolitan Washington Airports Authority says travelers should expect full flights, full luggage bins aboard airplanes and more gridlock near airports.

If you’re planning to park at the airport before flying out of town, book parking in advance.

“Build enough time into your journey to navigate through check-in and security, and to stop for a bite to eat or buy a gift,” MWAA spokesman Rob Yingling said. For future holidays, he said, travelers should consider enrolling in the Transportation Security Administration’s PreCheck program or U.S. Customs and Border Protection’s Global Entry program to take advantage of expedited screening at participating airports.

The TSA says air travelers should expect more lines Thanksgiving week, the year’s top holiday for travel. Many TSA officers will be working overtime to help handle the large numbers of travelers, an agency spokeswoman said.

The TSA reminds travelers of these tips and rules:

Arrive at the airport early enough to allow time to park, get your boarding pass, check your baggage and go through the security checkpoint. The agency recommends arriving at the airport two hours before a domestic flight. You can also save time by checking in online.

●Make sure your carry-on bag doesn’t contain any prohibited items — especially firearms and other weapons. Yes, this happens more often than you think. Firearms are allowed in checked luggage if packed properly and declared with your airline. If you’re wondering whether a particularly item is allowed, try the TSA’s “Can I bring my...” feature on its website at tsa.gov/travel.

●If you’re carrying liquids in your carry-on, you’re limited to 3.4 ounce or smaller containers that will fit in one sealed, clear, quart-size zip bag — and one bag per person. Make sure you take the bag out of your carry-on before sending it through the X-ray. In addition, take off your belt, shoes, coat/jacket and empty your pockets before you get to the X-ray machine so as to not hold things up. Senior citizens and children younger than 12 are allowed to keep their shoes on.

On the rails, the Tuesday and Wednesday before Thanksgiving and the Sunday after the holiday promise to be the busiest. Rail passengers should carry photo identification at all times, Amtrak said, because it may be requested aboard trains.

Amtrak is adding trains and seats on several routes across the country. In the Northeast Corridor, the Acela Express and Northeast Regional services will run full and extended schedules with more trains to expand capacity between Washington and Boston, Amtrak said.

And, just in time for the holidays, Amtrak recently upgraded WiFi on its Acela trains to make connectivity six times faster, part of upgrades to passenger service in the Northeast Corridor.

Have fun and safe travels.