SP-3: Investigation, Development and Evaluation of a Universal Securement Interface Standard and Wheelchair Docking Technologies

Importance of the problem

Description of the need and target population

An increasing number of people with disabilities use wheeled mobility devices (WMDs) (i.e., traditional manual and powered wheelchairs, powered bases, scooters, specialty strollers) as a means of accessing public and private transportation. For many, the ability to remain seated in their WMD while riding in a transport vehicle is the only feasible means of gaining access to education, work or recreational activities.

It is generally recognized that both the occupant restraint and the WMD securement must act together as an integral crash protection system. There are essentially two basic approaches to the securement of WMDs that are in common use today, attendant-operated securement systems and mechanical latching or docking devices. The attendant-operated type is the recognized industry standard dominated by the four strap-type system that attaches to the WMD frame. Use of docking securement devices is currently limited mainly to private vehicle applications, due primarily to the need to match wheelchair securement geometry with vehicle anchorage geometry. One exception is an experimental device developed by the University of Oregon (Hunter-Zaworski, 1992 a&b), which has not been widely accepted in public transportation.

While the four-point, strap-type securement system has been shown to be one of the most effective and versatile methods for securing a wide range of wheelchairs, it is also a system that is difficult and time consuming to use. Creating logistical problems in the public-transit environment (Hunter-Zaworski, 1992 a&b). Additionally, laboratory tests have indicated that existing strap-type systems may be at the upper limits of their strength capacity when tested at the nominal 30 mph/20g crash pulse (Fisher, Seeger et al., 1987). This implies that many heavier models of powered WMDs may not be secure at the nominal crash load levels. Also, users of transit vehicles have expressed dissatisfaction with operators having to fumble around their legs while fastening or disengaging the WMD securement devices. In addition, due to the difficulty and inconvenience of using belt and strap systems, they are often simply not used at all, or are not fastened in a way that provides adequate crash protection. Finally, current strap-type securement devices are inconsistent with the intent of ADA, which is to provide persons with disabilities increased access to community resources through improved independent use of public transportation systems.

Several docking devices have been commercially available for many years, others remain experimental. These devices require matching components, one attached to the WMD frame and the other to the vehicle (Hunter-Zaworski, 1992a&b). These devices offer increased user independence, but rely on having a location on the WMD to which one component of the securement system can be attached. As mentioned above, most WMDs do not have appropriate securement attachment locations. Also, since there are such a wide variety of WMD frame configurations, this necessitates a large number of securement hardware adapters, each of which needs to be safety tested.

Docking devices have been shown to work reasonably well for private vehicles in which the matching components can be individually configured to the specific wheelchair and vehicle. This has yet to happen in public vehicles that must be able to accept any WMD in order to be universally applicable. However, these early docking devices represent a departure from the four-strap tiedown approach, and, therefore, represent a first step towards a more universal and user-independent solution. However, the existing docking designs do not provide a universal solution to the public transit situation where the majority of WMDs are used.

ANSI/RESNA-SOWHAT, SAE WTORS and ISO-WG-6 standards development groups are now addressing many of these safety, incompatibility and inconvenience issues. At the present time, the above groups have completed the first stage of industry performance standards for transport WMDs and wheelchair tiedown (strap-type) and occupants restraint systems (WTORS). These harmonized national and international standards feature requirements for: design requirements, performance criteria and information disclosure, plus test methods to verify device compliance with the standards. During this time, all three standards Working Groups were chaired by Douglas Hobson the lead investigator on this project (Hobson, 2001). Dr Lawrence Schneider, a co-investigator on this project, currently chairs the combined ANSI/RESNA-SOWHAT and SAE working groups.

In an effort to foster the development of a universal industry design standard for the interface hardware between WMDs and docking-type securement devices, the RERC on Wheeled Mobility research team at the University of Pittsburgh hosted a series of important collaborative summit meetings in 1995-96 (Hobson, Bertocci et al., 1999). Senior technical representatives from the leading WMD companies, in addition to users and researchers, attended the meetings at which several significant decisions were made. First, the collective body agreed to pursue the concept of a standard (universal) interface as being fundamental to the successful development and marketing of docking securement devices. Second, draft specifications for the geometry of a proposed Universal Interface Device Geometry (UIDG) standard were established. And finally, after considerable deliberation on alternate approaches to hardware configuration, a U-shaped tubular structure mounted on the rear of WMD was deemed the most practical interface configuration. Further investigations were conducted by the University of Pittsburgh team to confirm these preliminary decisions. This led to the submission and approval of a new ANSI/RESNA-SOWHAT work item for an industry UDIG standard, which commenced in spring-summer of 1999. It also was placed on the work agenda of the parallel working group within the International Standards Organization (ISO). Harmonized work is now proceeding within both bodies, but is currently in urgent need of continued leadership, laboratory testing and demonstration technologies.

All standards compliance testing to date, for both WTORS and transit wheelchairs, use a 30mph/20-g crash pulse. This “high-g” pulse is consistent with that used in auto safety testing. However, there is evidence (as described in Task SP-1c) that suggests that this high level of crash pulse is excessive for situations involving WMD securement in large transit vehicles. For example, in Europe and Canada, it is becoming accepted practice to allow WMDs to ride on transit vehicles with only passive securement. The rider wheels into a rearward- facing WMD station that has a padded vehicle–mounted bulkhead located behind the head and backrest of the WMD rider. Securement from rotation into the aisle is dependent on a vertical floor to ceiling stanchion. Rearward movement is dependent on the arm strength of the user and the WMD brakes. Laboratory tests done at the RERC on Wheeled Mobility indicated unreliable performance of WMD brakes. In addition, varied upper-limb function of WMD users strongly suggests that both other passengers and the WMD user are at risk of injury, even during situations of emergency driving (e.g., maximum braking, rapid swerving) when WMD brakes are solely relied upon. Also, up-hill driving of the transit vehicle on hills with a slope greater then 10° is likely to cause uncontrolled rearward sliding of the WMD. Any type of vehicle collision from the side or rear could be devastating for both the WMD rider and other close-by passengers. However, recognition and acceptance of the reality that the securement loads are much lower in large transit vehicles opens the door for the development of lower-g standards and products that address this transport need.

In summary, the transportation of WMD users in the United States and most countries is in a state of confusion and chaos. The manifestations are that most WMD users are inconvenienced, transportation time and costs are unnecessarily high, WMDs are being unnecessarily damaged, legal liabilities are pervasive, and most importantly, provisions for user safety in many cases are either seriously compromised or overly prescribed.

The Tasks of this Priority have been formulated to build on the previous achievements of the RERC on Wheeled Mobility related to docking technology and the ongoing synergy of the standards development efforts, with the goal to establishing a universal docking interface geometry (UDIG) standard that will permit enhanced independence and safety in WMD securement. Once a harmonized UDIG standard has been adopted, it is reasonable to expect that a variety of compliant commercial docking devices and compatible transport wheelchair options will emerge on the market place. One Task of this priority will investigate opportunities for product innovation that address securement needs in the “low-g” large transit environment. The other Task will investigate opportunities for product innovation that address securement needs in the "high-g" private vehicle environment.

Beneficial impact on target constituency, including service providers

Adoption of universal docking technology for securement of WMDs for use in both private and public transport vehicles will have a profound impact on both increased independence and stigma reduction for WMD users wanting hassle-free securement. For transit authorities it will resolve many of the time-loss problems and the necessity for the operator to leave his/her driver-station to attend to the WMD securement station. It will also increase overall safety of WMD users by increasing the securement usage rate and minimizing strap application errors. This will not happen immediately, but will require a phase-in period of 5-10 years as new vehicles and WMDs are acquired. In the longer term, this development has the real potential of impacting virtually every WMD user either requiring or seeking enhanced and independent WMD securement in a motor vehicle.

Based on the success of past RERC’s preparatory work and the existence of a receptive national and international standards setting environment, the time to move forward with vigor on this exciting initiative is now.

Responsiveness to priority

This task responds to announced priority SP-3: “Investigate, develop and evaluate universal securement interfaces that would enable wheelchair and scooter users to safely and independently secure their wheelchairs and scooters to motor vehicles.”

Overall objectives

The specific aims of this project are:

  1. Providing investigative and laboratory support towards the development of the ANSI/RESNA and ISO universal docking interface geometry (UDIG) standard
  2. Providing investigative and technological innovations as necessary to facilitate the development and implementation of securement solutions for use in the “low-g” transport environment, and
  3. Developing demonstration docking technologies for use in the “high-g” securement environment for private vehicles.


Fisher, W., Seeger, B. and Svensson. (1987). “Development of an Australian Standard for wheelchair occupant restraint assemblies for motor vehicles.” Journal or Rehab Research and Development 24(3): 23-24.

Hobson, D. (2001). “Wheelchair Transport Safety - Evolving Options.” Journal of Rehab Res & Develop 37(5): vii-xv.

Hobson, D. A., Bertocci, G. E. and Karg. (1999). Focus Group Meeting: Universal interface and wheelchair integrated occupant restraint. University of Pittsburgh. Unpublished.

Hunter-Zaworski, KM, Ullman, DG, Herling, DE. Application of the Quality Functional Deployment Method in Mobility Aid Securement System Design: Vol. 1. Federal Transit Administration, Washington, DC, Report No. FTA-OR-11-0006-92-1, Dec 1992a.

Hunter-Zaworski, KM, Zaworski, JR, Clarke, G. The Development of an Independent Locking Securement System for Mobility Aids on Public Transportation Vehicles: Vol. 2. Federal Transit Administration, Washington, DC, Report No. FTA-OR-11-0006-92-2, Dec 1992b.

Last updated: March 17, 2002