Rear cameras are more effective than parking sensors at helping drivers avoid objects while traveling in reverse, but they don't help in every situation, a new IIHS study shows.
The study, conducted with volunteer drivers in an empty parking lot in the Los Angeles area, indicates that cameras would help prevent more backover crashes into pedestrians in the vehicle's blind zone than parking sensors. Surprisingly, cameras by themselves worked better than sensors and cameras combined.
Rearview camera display in a 2014 Audi A6
"Right now cameras appear to be the most promising technology for addressing this particularly tragic type of crash, which frequently claims the lives of young children in the driveways of their own homes," says David Zuby, the Institute's executive vice president and chief research officer.
An estimated 292 people are killed and 18,000 injured each year by drivers who back into them, usually in driveways or parking lots. Young children and elderly people are most likely to be killed in such crashes. Backover risk is increased by the large blind zones of many vehicles, which prevent drivers from seeing objects behind the rear bumper, especially objects that are low to the ground. SUVs and pickup trucks typically have the biggest blind zones, and they are involved in more backover crashes than cars.
Measuring blind zones
The research with volunteer drivers was the second of two IIHS studies that looked at how parking sensors and backup cameras increase visibility and help drivers avoid backovers. The first one measured the visibility of children to an average-size male driver in 21 vehicles, all 2010-13 models, and the degree to which each kind of technology improved visibility and detection.
In the visibility study, researchers used a pole painted with different bands to represent the average height and head size of a 12-15 month-old, a 2½-3 year-old and a 5-6 year-old. The pole was placed at various points behind each vehicle to see which portions of it were visible. The band representing the 12-15 month-old was much harder to see than the bands representing older children. On average, if it was anywhere within about 27 feet of the rear bumper, it couldn't be seen using glances and mirrors alone.
Without added technology, large SUVs were found to have the worst rear visibility, while small cars had the best. In general, the larger the vehicle, the worse the visibility.
However, the Hyundai Sonata, a midsize car, was an exception. At 263 square feet, its blind zone for a 12-15 month-old was 42 percent larger than that of the F-150 pickup truck. The Sonata's large blind zone is due in part to an extremely sloped rear window and tall rear trunk lid, while the F-150 benefited from large side mirrors designed to help with towing.
Backup cameras reduced the blind zone by about 90 percent on average. Parking sensors, which use ultrasonic sound waves or radar to detect objects around the vehicle, also reduced blind zones, but not as much. In the eight vehicles that had both technologies, the parking sensors had a small added benefit of 2-3 percentage points beyond the reductions provided by the cameras alone.
Rear visibility in a typical SUV: 2013 Chevrolet Equinox LTZ
This diagram shows how a rearview camera improves a driver's field of view in a typical SUV. It depicts the visibility of an average 12-15-month-old child (30 inches tall) behind the Chevrolet Equinox LTZ, using the camera, as well as mirrors, an over-the-shoulder glance and rear parking sensors. On its own, the camera would provide visibility in most of the space measured, but would leave areas near the bumper where a child couldn't be seen. When the camera is used in combination with the side mirrors and parking sensors, the blind zone — represented by the area that remains white when all buttons are clicked — is greatly reduced but doesn't disappear entirely. Relying on a right shoulder glance alone, the child would be visible only off to the right of the SUV and starting 35 feet from the rear bumper. Little if any of the area being measured would be covered by a left shoulder glance, and for that reason it isn't included in the diagram.
How drivers use technology
The study with volunteer drivers built on this work by allowing researchers to see how drivers use the technologies and whether they prevent crashes.
The analysis was based on the experience of 111 volunteers using a 2013 Chevrolet Equinox LTZ. The Equinox was chosen because it was a high-volume midsize SUV, and in the earlier visibility measurements it had neither the smallest nor the largest blind zone. The purpose of the study was disguised from the volunteers, who were told they were there to evaluate the SUV's entertainment and information systems. After completing some parking maneuvers and tasks such as tuning the radio and reading from a navigation display, they were then told to back out of a spot and return to where they had left their personal vehicles. As they backed out, a foam cutout of a child-size crash test dummy was put in the vehicle's backing path.
In some cases, the foam dummy was stationary behind the vehicle, while in other cases it moved into the vehicle's path from the driver's side. Few of the volunteer drivers hit the object if it was moving, and neither the backup camera nor the parking sensors provided a statistically significant benefit in those cases. The proportion of drivers who collided with the stationary object was 4 times as large as the proportion that collided with the moving object. Drivers with the rearview camera alone had the fewest collisions with the stationary object; 56 percent of them hit it. In contrast, all the drivers who had no technology hit the stationary object, while parking sensors alone helped just 1 out of 16 drivers avoid a crash.
For drivers who had both the camera and the sensors, the benefit wasn't as great as with the camera alone. Three-quarters of these drivers hit the stationary object. It may be that the sensors, which detect objects up to 8 feet behind the vehicle at speeds less than 5 mph, gave drivers a false sense of security, so they paid less attention to the camera display. Slightly fewer drivers who had both cameras and sensors looked at the camera display at least once than drivers who had only cameras, and they spent a smaller proportion of time looking at the camera display while backing, but these differences weren't statistically significant.
"The sensors might be more useful if they had a larger range and could provide an earlier warning," says David Kidd, an IIHS research scientist and the lead author of both studies. "Even when drivers braked in response to the sensor, few collisions were prevented."
Rearview cameras didn't prevent all collisions, even when properly used. When the stationary object was in the shade, for example, nearly every driver who looked at the display still hit it. In the real world, weather and lighting conditions would likely affect the usefulness of cameras. These issues may help explain why HLDI didn't find consistent reductions in insurance claims when it studied camera systems offered by Mazda and Mercedes-Benz (see Status Report special issue: crash avoidance, July 3, 2012).
The research into backing technologies comes as the National Highway Traffic Safety Administration (NHTSA) is considering whether to require cameras on passenger vehicles. Congress directed the agency in 2008 to expand the required field of view behind a vehicle. NHTSA hasn't yet finalized the regulation but previously indicated that cameras are the only technology available that could meet the congressional mandate. The agency announced in September 2013 that it would be adding rearview cameras to the list of recommended features in its vehicle safety ratings.
In comments to NHTSA, the Institute has said it supports efforts to encourage rearview cameras. At the same time, it has urged the agency to require that a certain minimum amount of space around a vehicle be directly visible using backward glances and mirrors.
"Having an available rearview video system on a vehicle model should not justify design choices that restrict direct visibility around the vehicle," the Institute wrote in a July comment.
Manufacturers also may be able to improve the technological options. Both cameras and sensors likely would be more effective if they were combined with automatic rear braking technology. Autobrake for front crash prevention has been found to be more effective at preventing or mitigating frontal crashes than warning systems alone.