Though there are rules in place to ensure that bumpers on cars from different brands line up with each other, there are no such restrictions on SUVs, resulting in costly repair bills when collisions occur, according to a new study.

The U.S. Insurance Institute for Highway Safety released a report Thursday after performing crash tests to measure the impact of the mismatched bumper heights.

"Bumpers are supposed to bump and engage each other in crashes to prevent costly damage to the parts of the vehicle that are expensive to repair," Russ Rader, of the IIHS, told CTV's Canada AM.

"And because of lax regulations, cars and SUVs share the road but they don't share the same bumper rules."

While cars are required to have bumpers that protect a zone from 16 to 20 inches off the ground, SUVs, along with pick-up trucks and minivans, have no such requirement.

The result is that when cars crash into each other, the bumpers usually line up. But when the crash involves a car and an SUV, the bumpers are likely to miss each other and cause much more damage.

The IIHS tested SUVs and cars travelling 16 kilometres per hour in front-into-rear collisions involving seven pairs of 2010-2011 models. Each pair included a small car and SUV from the same automaker.

"We picked vehicles from the same manufacturer because we think automakers should at the least pay attention to bumper compatibility across their own fleets," explained Joe Nolan, the Institute's chief administrative officer in a release.

"The results show that many don't."

When the Nissan Rogue SUV crashed into the back of the Nissan Sentra, the Rogue's higher bumper overrode the Sentra's. The damage was significant, with a US$7,444 combined repair bill -- and the Rogue was rendered inoperable.

When the Ford Escape was hit from behind by the Ford Focus, the Focus's bumper passed directly under the Escape's, resulting in $5,203 in damage to the car and $2,208 for the SUV.

When the order was reversed and the Escape hit the Focus from behind, the result was similar. In that case the bumpers did overlap slightly, but by a margin of less than two inches -- not enough to absorb the impact. As a result the Focus' rear body and trunk lid received $3,386 in damages from the crash.

There was also significant damage when the Toyota RAV4 and Corolla were paired up. But it wasn't due to the fact the bumpers didn't line up, but the fact the RAV4's rear bumper is little more than a "stamped piece of sheet metal supporting the bumper cover" -- another result of lax bumper regulations.

The Corolla hit the RAV4 from behind, and because the bumper didn't absorb the impact properly, the car hit the spare tire mounted on the RAV4's tailgate. As a result the car's hood, grill, headlights, air conditioner and radiator were damaged, and the RAV4's tailgate and rear body panels were damaged.

The result was almost $10,000 in combined damages.

The results of the Honda tests were among the best, with the CR-V and Civic bumpers lining up better that most other pairs. Half of the bumper face on the Hondas overlapped with each other.

"The CR-V's front bumper overlapped the Civic's rear bumper by more than 2 inches. That may not sound like much, but it's enough to allow the bumpers to do what they're supposed to do," Nolan says.

The combined crash damage between the two Hondas was $2,995 -- the lowest in the test group. The damage to the Civic was just $1,274.

But even among the best performers, the results were still not exceptional, the IIHS said, suggesting that better regulations are urgently required.

"Of the seven car-SUV pairs we tested, we can't point to a single one as a model of compatibility because combined damage estimates run into thousands of dollars for even the best performers," Nolan said.

"In the real world that money comes straight out of consumers' wallets through deductibles and insurance premiums. Regulating SUV bumpers would ease the burden."

Following are some of the most dramatic results from the study:

Toyota Corolla into Toyota Rav4:

  • SUV damage: $6,015
  • Car damage: $3,852

Nissan Rogue into Nissan Sentra:

  • SUV damage: $2,884
  • Car damage: $4,560

Jeep Patriot into Dodge Caliber:

  • SUV damage: $1,415
  • Car damage: $3,095

VW Golf into VW Tiguan:

  • SUV damage: $1,872
  • Car damage: $4,555