Whiplash is the most common type of injury in motor vehicle accidents and properly adjusted head restraint can have a big effect on reducing or even eliminating many whiplash injuries. As a result, pressing car makers and governments for improved head restraint design has been high on the agenda for many years. Federal Motor Vehicle Safety Standard (FMVSS) 202 required that all passenger cars manufactured for sale in the US after December 31, 1968 includ head restraints in the front outboard seating positions. The installation of head restraints in the front seats of Australian vehicles has also been compulsory since 1972 under Australian Design Rule (ADR) 22. The early research recommended that making head restraints compulsory in rear seats was not justified because of the small number of neck injuries that occurred in rear seated occupants (Maher, 2000)
This section focuses primarily on the US, Canada, and Europe standards, and describes how the standards from different countries were harmonized to develop a global technical regulation on head restraints. A summary of the various vehicle rating systems for head restraints is also provided.
Standards and Regulations
Vehicle manufacturers have been required to equip vehicles with head restraints since 1969 in the US, and since 1978 in Canada and in Europe. The European regulations include a minimum height of 750 mm (29.5 in) and restraints must be adjustable to 800 mm (31.5 in) above the seating reference point.
The US Motor Vehicle Safety Standard 202, in effect from 1969 to September 2009, required that head restraints be adjustable to a height of 700 mm (27.6 in) above the position of the center of rotation of the hip joint when a person is seated in the vehicle (seating reference point) (Kahane, 1982). This was problematic because the head restraints were not as high as the center of gravity of an average male’s head.
In Canada, the safety standard enacted in 1978 was aligned with the US requirements for head restraints. The final rule modifying the requirements of safety standard 202 of the US was published in December 2004, and amended in May 2007. The new requirements increased the minimum height of the outboard head restraints from 700 to 750 mm, and introduced a maximum backset requirement, maximum gap requirement between the head restraint and seat and required testing for height retention and energy absorption (Department of Transport, 2008). There were also more stringent testing requirements for strength testing and backset retention and a new dynamic testing protocol with updated male test dummies (Department of Transport, 2008).
The amendment that is proposed for 2009 in both the US and in Canada, is a stepping stone toward international harmonization of head restraint requirements (Department of Transport, 2008), that will be developed as a global technical regulation.
An ad hoc informal working group on head restraints has been meeting since 2004 to discuss and evaluate issues surrounding the requirement of head restraints in vehicles, with the main goal of making recommendations concerning the development of a global technical regulation for head restraints. At a meeting in June 2006, the group began developing a proposal for a draft global technical regulation that was based on the requirements of the United Nations Economic Commission for Europe’s (UNECE) Regulation 17, Regulation 25, and the upgraded FMVSS 202 (FMVSS 202a).
The group made several recommendations for the development of a global technical regulation, which are summarized below (Ad hoc Group on Head Restraints, Meeting Minutes June 23, 2006).
Head Restraint Height:
For front outboard head restraint height, the recommendation was to increase to 850 mm above the reference point to accomodate taller populations. However, based on the evidence, it was determined that the current 800 mm was sufficient to protect the 95th percentile Netherlands male (tallest in the world). For rear outboard head restraint height, a 750 mm minimum height and static requirements, excluding backset was recommended. For front center, it was recommended that the head restraint conform to the same regulations as the rear outboard head restraints (optional, no backset requirement, 750 mm height). For the rear center, the requirements were the same as front center, although no height requirement was necessary (Ad hoc Group on Head Restraints, Meeting Minutes June 23, 2006).
Backset:
In 2004, discussions continued on this parameter. There was concensus that a recommendation for backset was important, yet the 55 mm requirement may be too stringent. Issues arose regarding measurement methods and occupant comfort levels (Ad hoc Group on Head Restraints, Meeting Minutes June 23, 2006).
Dynamic Test:
An optional dynamic test was proposed as an option to the static requirements. Concerns arose surrounding which type of dummy to use. The Hybrid III dummy spine is not humanlike, nor is its motion during a dynamic test; however, the BioRID dummy, although preferred, is not ready to be made part of a regulation. It was decided that the dynamic test could be phased into the proposal at a later time (Ad hoc Group on Head Restraints, Meeting Minutes June 23, 2006).
At the group’s seventh meeting, Canadian representatives presented their findings on the use of the Head Restraint Measuring Device (HRMD), created by the Insurance Corporation of British Columbia (ICBC), which was used for measuring backset. The testing confirmed that the HRMD provides repeatable and reproducible results, and that increasing the number of measurements reduces the backset variability (Gane & Pedder, 1996). The global technical regulation will include the use of the HRMD (Department of Transport, 2008).
The work of this group has now led to agreement regarding the parameters of a global technical regulation for head restraints, which was approved in March 2008. Due to non-consensus regarding dynamic testing only quasi-static testing requirements will be included in the global technical regulation. Work is underway to develop an internationally accepted dynamic testing protocol (Department of Transport, 2008).
In the US, 2009 will be a pivotal year for head restraints and and the prevention of whiplash. All 2009 vehicle models must include the mandated requirements of head restraints to all front seats as well as back seats. These include: a minimum of 29.5 inches (750 mm) from an occupant’s hip to the top of the head restraint and the backset must be 2 inches (50.8 mm) between the head and the head restraint (IIHS, 2005).
Benefits of harmonization
The approved harmonization of standards and regulations into a global technical regulation combined elements from the UNECE Regulations No.17, No. 25, and the newly upgraded US FMVSS 202a. International motor vehicle manufacturers, along with the entire industry benefit from harmonization and new technology-based improvements to the head restraint regulations. The benefits to industry include the improved safety of the head restraints, leveraging of resources, and the harmonization of requirements. Industry also benefits from a reduction in the cost of development, testing and the fabrication process of new vehicle models. Consumers worldwide benefit by having a choice of vehicles built to higher, globally recognized standards, providing an improved level of safety at a lower cost.
Safety Ratings
The regulations for head restraints were not completely effective in rear collisions, which lead to enormous costs for insurance companies; therefore, whiplash received considerable attention. It was a significant issue for insurance companies, vehicle manufacturers had to design improved head restraints that were appropriate for the majority of the driving and occupant population, and there was consumer pressure. This requirement has resulted in numerous rating systems for seats and head restraints (Avery et al., 2007). The current ratings include: the International Insurance Whiplash Prevention Group (IIWPG) ratings, the Swedish Road Administration (SRA) ratings, Federal Motor Vehicle Safety Standard (FMVSS) ratings and more recently, the European New Car Assessment Programme (Euro NCAP) ratings, which are a combination of the IIWPG and SRA systems.
IIWPG Rating System
The IIWPG utilizes a two-stage process for evaluating and rating the ability of seats and head restraints to prevent neck injury in moderate and low-speed rear-end impacts (IIWPG, 2004). First, the static geometry of the head restraint is measured and rated; second, a dynamic evaluation in a simulated rear-end collision is conducted and rated. The static geometry measurements include height and horizontal distance to the back of the head. Head restraints with geometric ratings of ‘acceptable’ or ‘good’, then go on to dynamic testing in a simulated 16 km/h rear impact to obtain a rating for how well the torso, neck and head are supported (IIWPG, 2004). The results of the geometric measurements and the dynamic testing are combined to produce an overall rating of the seat and head restraint as a whole (IIWPG, 2004).
The dynamic testing involves seat design parameters (time-to-head restraint contact; energy-absorbing characteristics) and test dummy response parameters (neck shear force; neck tension force). The simulated rear collision is tested using a sled device and a BioRID II crash dummy (IIWPG, 2004).
The detailed instructions for testing static geometry are available in the Procedure for Evaluating Motor Vehicle Head Restraints (RCAR, 2001), while the procedure for conducting dynamic testing is described in IIWPG Protocol for the Dynamic Testing of Motor Vehicle Seats for Neck Injury Prevention (RCAR, 2004).
Swedish Road Administration (SRA) Ratings
The Swedish Road Administration (SRA) partnered with Folksam Insurance and Autoliv in 2003 to publish vehicle seat ratings based on dynamic testing. Three tests are conducted using varying speed/acceleration levels, and three BioRID dummy response parameters (NIC, Nkm, head- rebound velocity) to create a rating score (Krafft et al., 2004). Five points are assigned to each of the three tests to create a maximum combined rating of 15 points. The points are assigned based on the magnitude of the measured value. Once all points are combined, the vehicle seats are rated using a color system of Green+ (0-2.5 points), Green (2.6-5.0 points), Yellow (5.1-10.0 points), or Red (10.1-15.0 points). Based on the points system, Red is the worst rating and Green+ is the best.
European New Car Assessment Programme (Euro NCAP) Ratings
The Euro NCAP ratings were developed in 2008 using a combination of parameters from the IIWPG and SRA ratings. The testing uses a dummy to assess the head restraint geometry and dynamic testing of the seat, using three impact severities of high, medium, or low (Euro NCAP, 2008). The rating also includes parameters such as ease of use (adjustment), locking of the head restraint, and overall seat reliability. The overall whiplash score calculated as a combination of head restraint/seat geometry and outcome of the dynamic tests, results in a rating of ‘good’, ‘marginal’, or ‘poor’ (Euro NCAP, 2008).
Throughout the US, Canada and Europe, rating systems have evolved over time in an attempt to be as comprehensive as possible to ensure driver and passenger safety. Driven by a need to reduce insurance claims and the motivation of consumer awareness, the set of ratings that are currently in use are based on high caliber research and testing. The evolution of standards, regulations and rating systems has combined to develop safer vehicles in an effort to reduce the occurrence of neck pain and whiplash injury.