Car safety seats for children: rear facing for best protection.

OBJECTIVE: To compare the injury risk between rear-facing (RFCS) and forward-facing (FFCS) car seats for children less than 2 years of age in the USA. METHODS: Data were extracted from a US National Highway Traffic Safety Administration vehicle crash database for the years 1988-2003. Children 0-23 months of age restrained in an RFCS or FFCS when riding in passenger cars, sport utility vehicles, or light trucks were included in the study. Logistic regression models and restraint effectiveness calculations were used to compare the risk of injury between children restrained in RFCSs and FFCSs. RESULTS: Children in FFCSs were significantly more likely to be seriously injured than children restrained in RFCSs in all crash types (OR=1.76, 95% CI 1.40 to 2.20). When considering frontal crashes alone, children in FFCSs were more likely to be seriously injured (OR=1.23), although this finding was not statistically significant (95% CI 0.95 to 1.59). In side crashes, however, children in FFCSs were much more likely to be injured (OR=5.53, 95% CI 3.74 to 8.18). When 1 year olds were analyzed separately, these children were also more likely to be seriously injured when restrained in FFCSs (OR=5.32, 95% CI 3.43 to 8.24). Effectiveness estimates for RFCSs (93%) were found to be 15% higher than those for FFCSs (78%). CONCLUSIONS: RFCSs are more effective than FFCSs in protecting restrained children aged 0-23 months. The same findings apply when 1 year olds are analyzed separately. Use of an RFCS, in accordance with restraint recommendations for child size and weight, is an excellent choice for optimum protection up to a child's second birthday.

Frontal sled tests comparing rear and forward facing child restraints with 1-3 year old dummies.

Although most countries recommend transitioning children from rear facing (RF) to forward facing (FF) child restraints at one year of age, Swedish data suggests that RF restraints are more effective. The objective of this study was to compare RF and FF orientations in frontal sled tests. Four dummies (CRABI 12 mo, Q1.5, Hybrid III 3 yr, and Q3) were used to represent children from 1 to 3 years of age. Restraint systems tested included both 1) LATCH and 2) rigid ISOFIX with support leg designs. Rear facing restraints with support legs provided the best results for all injury measures, while RF restraints in general provided the lowest chest displacements and neck loads.

Quantifying the relationship between vehicle interior geometry and child restraint systems.

The prevention of interactions of children or child restraints with other vehicle structures is critical to child passenger safety. Fifteen current vehicles and seven rear and forward facing child restraint systems were measured in an attempt to quantify the available distance between child restraints and these vehicle structures. Rear facing child restraints exhibited such small amounts of clearance that contact would be expected in the majority of frontal crashes. Upper tethers are critical in the prevention of head contact, while head contact is likely when the upper tether is not used.

Vehicle interior interactions and kinematics of rear facing child restraints in frontal crashes.

The performance of rear facing child restraints in frontal crashes can be determined by controlling a) the child's kinematics and b) interactions with vehicle structures. Twelve sled tests were performed to analyze the effect of the location and structural properties of vehicle interior components. The role of restraint kinematics was studied by developing computational models which underwent idealized motions. Stiff structures originally offset from the restraint, but which contact the restraint late in the test, cause increased injury values. Attachment methods which reduce child restraint rotation and more rigidly couple the restraint to the vehicle result in the best safety performance.

The performance of various rear facing child restraint systems in a frontal crash.

Current forward facing (FF) child restraint designs use LATCH and ISOFIX systems to couple the restraint to the vehicle. Rear facing (RF) child restraints, however, have multiple coupling methods that vary by manufacturer and country of origin. Sled tests were performed with the CRABI 12 month dummy in six different RF attachment conditions. The performance of the rear facing child restraints (restraint kinematics, head accelerations, and neck loads) was highly dependent on the coupling method used. The results were also compared to a FF LATCH restraint.

Prediction of cervical spine injury risk for the 6-year-old child in frontal crashes.

This article presents a series of 49 km/h sled tests using the Hybrid III 6-year-old dummy in a high-back booster, a low-back booster, and a three-point belt. Although a 10-year review at a level I trauma center showed that noncontact cervical spine injuries are rare in correctly restrained booster-age children, dummy neck loads exceeded published injury thresholds in all tests. The dummy underwent extreme neck flexion during the test, causing full-face contact with the dummy's chest. These dummy kinematics were compared to the kinematics of a 12-year-old cadaver tested in a similar impact environment. The cadaver test showed neck flexion, but also significant thoracic spinal flexion which was nonexistent in the dummy. This comparison was expanded using MADYMO simulations in which the thoracic spinal stiffness of the dummy model was decreased to give a more biofidelic kinematic response. We conclude that the stiff thoracic spine of the dummy results in high neck forces and moments that are not representative of the true injury potential.

Prediction of cervical spine injury risk for the 6-year-old child in frontal crashes.

This paper presents a series of 49 km/h sled tests using the Hybrid III 6-year-old dummy in a high-back booster, a low-back booster, and a three-point belt. Although it is shown that non-contact cervical spine injuries are rare in correctly restrained children in this age group, neck loads exceeded published injury thresholds in all tests. The dummy kinematics were compared to the kinematics of a 12-year-old cadaver tested in a similar impact environment. This comparison was expanded using MADYMO simulations. It is concluded that the stiff thoracic spine of the dummy results in high neck forces and moments that are not representative of the true injury potential.