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An American institution, the successful family driving vacation has always relied on the ideal road-trip car.

In the iconic driving-vacation movie "National Lampoon's Vacation," Clark loads the entire Griswold family into a monstrosity called the Wagon Queen Family Truckster, resembling a cross between a "Mad Max" transport and a Pontiac Aztek. Things rapidly deteriorate from there.

Happily, today's road-trip planners have a far better selection of family cars, sports utility vehicles, minivans and crossover SUVs.

Basic requirements for an ideal road-trip car include good fuel economy, a roomy interior and an affordable price. Here are five vehicles that fulfill our core requirements and then some.

To appear on this list, a road-trip car must:

Retail for less than $35,000 (MSRP and delivery fees).

Achieve an Environmental Protection Agency-estimated 24 mpg or more on the highway.

Seat up to five passengers comfortably in front- and second-row seats.

Accommodate at least 30 cubic feet of cargo with its second-row seat in place.

Take your pick, pack a bag, load up the kids and hit the road.

2011 Ford Flex SE

Price: $29,995

Fuel economy: 17 mpg city/24 mpg highway

With exterior styling that gives a nod to the woodie wagons of the 1940s, the 2011 Ford Flex delivers a top-notch passenger experience.

With seating for up to seven, it has plenty of space for all but the largest of families. Legroom for the reclining second-row seat is a generous 44.3 inches; third-row passengers have 33.3 inches of legroom.

Behind the third-row seat is 20 cubic feet of cargo space. With the third-row seat folded down, cargo capacity swells to 43.2 cubic feet.

Output from a 262 horsepower, 3.5-liter V-6 engine rotates the front wheels via a six-speed automatic transmission.

Standard safety equipment includes six air bags, stability control and rear parking sensors. Flex received top marks in frontal and side-impact government crash tests.

The SE has the entry-level trim package, but still provides a long list of included features, such as full power accessories, remote keyless entry, tilt-and-telescoping steering wheel, trip computer, cruise control, automatic climate control, and a six-speaker audio system with CD player and auxiliary input jack.

2011 GMC Acadia SL

Price: $32,810

Fuel economy: 17 mpg city/24 mpg highway

Similar to Chevrolet's Traverse and Buick's Enclave, the 2011 Acadia relies on a 288 horsepower, 3.6 liter V-6 engine for its get-up-and-go. Engine power is funneled to the front wheels through a six-speed, driver-shiftable automatic transmission.

A 22-gallon fuel tank means that from fill up, Acadia has a highway range of up to 528 miles.

Capable of seating up to eight -- even the split-folding third-row seat can accommodate adults on shorter trips -- it makes for a great road-trip car. Second-row legroom is 36.9 inches and third-row is 33.2 inches

With the third-row seat in place, Acadia offers 24.1 cubic feet of cargo-carrying capacity. By folding the third-row seat, it opens up an additional 44.8 cubic feet of storage for a total of 68.9 cubic feet.

A full range of safety features typical for this segment, such as six air bags and stability control, are included. It scored well in government and Insurance Institute for Highway Safety crash tests.

Included in the base price of this road-trip car are full power accessories, front/rear air conditioning, cruise control, tilt-and-telescoping steering wheel, the OnStar system with a one-year subscription for navigation, and a six-speaker audio system with CD player and auxiliary input jack.

Honda Odyssey EX

Price: $31,730

Fuel economy: 18 mpg city/27 mpg highway

You can get an Odyssey LX for roughly $3,000 less than the EX, but we liked EX extras such as power-sliding side doors, an upgraded audio system and tri-zone, automatic climate control.

The Odyssey leads our list in rear legroom with 40.9 inches for second-row passengers and 42.4 inches for the third-row seat. Also impressive is cargo space with 38.4 cubic feet behind the third row and 93.1 cubic feet behind the second row.

Between fill ups, the potential highway-mileage range also tops this list at 567 miles.

Powering the front wheels is a 248 horsepower, 3.5 liter V-6 engine mated to a five-speed automatic transmission.

Safety features include six air bags and stability control. Odyssey performed well in government and Insurance Institute for Highway Safety crash tests.

Among the standard features not already mentioned: full power accessories, cruise control, tilt-and-telescoping steering wheel with redundant audio controls, trip computer, and a six-speaker audio system with subwoofer, CD player and auxiliary input jack.

2011 Subaru Outback 2.5i Limited

Price: $29,220

Fuel economy: 22 mpg city/29 mpg highway

Smaller families might want to opt for a vehicle with less of a footprint than a crossover or minivan. The 2011 Subaru Outback 2.5i Limited fits that bill.

A number of factors separate Outback 2.5i Limited from others on this list. It is the least pricey, seats a maximum of five, gets the best fuel economy, has a four-cylinder engine and has all-wheel drive.

Not just a summer road-trip car, the all-wheel-drive qualifies Outback for winter excursions as well.

A 2.5 liter, horizontally opposed, four-cylinder engine produces 170 horsepower that is hustled to all four wheels by a continuously variable automatic transmission.

Sporting the least interior space among vehicles on this list, Outback's rear-seat legroom is 37.8 inches, and cargo space behind the second-row seat is 34.3 cubic feet.

Notable among its safety features are six air bags and stability control. The Outback also scored well in crash tests.

Standard features include full power accessories; cruise control; tilt-and-telescoping steering wheel; heated front seats; trip computer; dual-zone, automatic climate control; and a nine-speaker Harmon Kardon audio system with a subwoofer, six-CD changer and an auxiliary input jack.

2011 Toyota Sienna SE

Price: $32,160

Fuel economy: 18 mpg city/24 mpg highway

With seating for up to eight passengers, the totally redesigned 2011 Toyota Sienna SE is a good choice for everyday family chores as well as a two-week road trip.

SE was the Sienna trim package chosen for this list because it has a second-row seat that accommodates three and a healthy list of standard features.

Legroom in the rear seats is decent: second-row 37.6 inches and third-row 36.3 inches. Likewise, cargo room is generous with 39.1 cubic feet of space behind the third-row seat and 87.1 cubic feet behind the second row.

It scored well in crash tests; six air bags as well as stability control are standard.

A 3.5-liter V-6 engine delivers 266 horsepower to the front wheels by way of a six-speed, driver-shiftable automatic transmission.

Toyota chose to stiffen the SE's four-wheel independent suspension for better handling.

In addition to 19-inch wheels and some stylish body cladding, the SE comes standard with full power accessories, triple-zone air conditioning, cruise control, tilt-and-telescoping steering wheel, trip computer, and a six-speaker audio system with CD player and auxiliary input jack.

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