But First, Let Me Buckle My Seatbelt

Designers: Virginia Durham, Michelle Seywald, Jennifer Sekar

Advisor: Lauren Zangari, OT

Supervising Professor:  Kevin Caves

Abstract. High school student John needs to be able to buckle and unbuckle his seatbelt, but his TAR syndrome limits his reach and makes it more difficult to grasp objects. To allow him to complete the task, two devices were made for him: (1) a telescoping multipurpose tool with a clip on one end for buckling and a sheath on the other for unbuckling and (2) a slack maintainer. The devices, when used in tandem, allow John to easily buckle and unbuckle his seat belt.


Our client, John, is a high school student with Thrombocytopenia Absent Radius (TAR) syndrome, which is characterized by a bilateral absence of the radial bones [1]. Individuals with TAR syndrome usually exhibit underdevelopment in other bones of the arm and hands, causing the hands to be located near the shoulder [2]. As a result of these symptoms, John experiences difficulty reaching and grasping objects.

Seat Belt 2015 Fig 1

Figure 1: View of the Buckling Mechanism Clip

John is looking forward to driving after being fitted for adaptive steering equipment. While he will be able to drive independently, our client currently needs assistance in buckling his seat belt. John can move the seat belt from its resting position to mid-chest level, but cannot bend his torso to reach the buckle or release the belt independently.

While no devices are made specifically for TAR syndrome, buckle extenders and seat belt handles could be adapted. Seat belt extenders fit into the existing buckle and have a rigid extension that brings the buckle closer to the driver and is available in lengths 3” to 8” [3]. Seat belt handles attach to the seat belt above the fitting and provide extended reach for those with limited mobility or arthritis [4]. Although one of these devices alone would not be sufficient for John, adapting the existing technology or using devices together may aid our client in buckling his seat belt.

Problem Statement/Project Goals.

The goal of the seat belt project is to develop a method enabling our client to buckle his seat belt independently. The product should not require modification to the existing seat belt safety system, and be removable so the client can use this device in driver and passenger seats of other cars. The adaptive steering equipment mentioned above will consist of a shoebox-sized steering wheel near his right shoulder and secondary controls by his left hand; the seat belt device must not interfere with this equipment. One of John’s concerns is how his use of adaptive equipment is perceived so the product must be unobtrusive, efficient, and easy to use. The device must adhere to all safety requirements as seat belts are subject to rigorous testing and strict regulations [5].

Design and Development.

Multi-tool: The current device is a multi-tool that features two distinct ends: a buckling end, an unbuckling end, and a telescoping pole linking the two.

Seat Belt 2015 Fig 2

Figure 2: View of the Unbuckling Mechanism

The fitting can be wedged into the buckling end to extend John’s reach, and the unbuckling end fits over the buckle to more easily depress the release button.

Buckling Mechanism: The buckling mechanism is a clip that holds the fitting of the seat belt while the client buckles himself in as seen in Figure 1. The clip is approximately the width of the fitting, creating strong grip that holds the fitting securely. A hollow, stainless steel rod was flattened at the clip end and attached with two bolts, while the other end was inserted into the end of the telescoping pole and secured with a screw.

Unbuckling Mechanism: The unbuckling mechanism consists of a box without the front and bottom sides, and a protrusion from the top shown in Figure 2. The mechanism fits over the buckle to stabilize the device and can be pressed down to release the seat belt. There is a cylinder on the top of the device that fits into the telescoping pole and is attached with two screws. The unbuckling mechanism was 3D printed in the strongest of the 3D print plastics available at Duke, acrylonitrile butadiene styrene (ABS), and coated with XTC-3D epoxy to resist the compressive force necessary to unbuckle the seat belt.

Seat Belt 2015 Fig 3

Figure 3: Selfie Stick and Twist-Locking Mechanism

Telescoping Pole: The buckling and unbuckling mechanism are attached on either end of aluminum telescoping pole adapted from a selfie stick so John can collapse and store the device. At its shortest, the multi-tool measures 14 in. long, extends up to 31.5 in., and can be locked at any length in between though a clockwise twist locking mechanism shown in Figure 3. The telescoping pole allows John to extend his limited reach in order to buckle and unbuckle his seat belt.

Slack Maintainer: In addition to the buckling and unbuckling multitool, we also created a device to maintain the slack that John pulls out while buckling. The device consists of a foldable base with a fringed dycem tip as seen in Figure 4a. The slack maintainer sits below the seat belt source on the wall of the car and can be disengaged after buckling. When pulling out the seat belt, the dycem tips fold away and allows for free movement of the seat belt. When the seat belt attempts to retract, the dycem tips are caught and wedged into the seat belt source, which maintains the generated slack (see Figure 4b). After buckling, John can pull on the soft handle to move the slack maintainer out of the way so the seat belt can retract for a snug fit.

Seat Belt 2015 Fig 4

Figure 4: a) Slack Maintainer b) Slack Maintainer In Use

In consulting with John’s occupational therapist, we have ensured this multi-tool and slack maintainer are ergonomic in their design and will be safe for our client to use (Figure 5).  In addition, this devices work together to fit all of our design specifications—the devices do not modify the car, are removable and portable, are compatible with the adaptive steering equipment and many vehicle types, fall under the $400 budget, and most importantly, do not interfere with the standard safety functions of the seat belt.


The multitool and slack maintainer have enabled our client to independently buckle and unbuckle his seat belt, a feat he was not previously able to accomplish. The multi-tool was evaluated to assess ease of use, compatibility with John’s force generation capabilities, durability, interference with existing seat belt safety system, extent of modification to the vehicle, degree of portability, use in different types of cars, and efficiency of design. This consisted of verification testing by the designers and validation testing by our client while using the devices. To test usability, we gave the device to John for a week to practice with, in addition to observing him use the device extensively during our client meetings. After measuring the forces our client could generate in both tension and compression, we designed the device such that the process of unbuckling and buckling did not exceed 10 lbs of force. Additionally, we ensured the device would be able to withstand use with a minimum safety factor of 2. The device can undergo 16 pounds of compression before sliding when fully extended and can experience 30 pounds when compacted without experiencing any deformation. It can experience 20 pounds of tensile force without sliding when both fully extended and compacted.

Seat Belt 2015 Fig 5

Figure 5: a) John using the Bucking Mechanism b) John using the Unbuckling Mechanism

Client satisfaction was measured through a questionnaire on the ease of use, independence, and utility (Appendix C). The results of the survey indicate that our client was overall very satisfied with the design and utility of the devices we created for him. In fact, we received perfect marks across the board, apart from the buckling mechanism, to which John only somewhat disagreed that it takes him a long time to use the buckling mechanism. We believe that with the practice of repeated use, and especially with the use of the slack maintainer, the speed with which our client is able to accomplish this task will rapidly increase.


To allow our client John to independently buckle his seat belt, we created two devices to be used in tandem. The first was a telescoping multi-tool with a clip on one end for buckling and a sheath on the other for unbuckling. The second was a slack maintainer that used fringed dycem to jam the seat belt and allow our client to pull the seat belt without it retracting. Both devices allow him to complete the task and when his car is fitted with the adaptive technology, he will be ready to drive independently.


[1] TAR syndrome. (2015, September 14). Retrieved September 16, 2015, from http://ghr.nlm.nih.gov/condition/thrombocytopenia-absent-radius-syndrome

[2] Wu, J., & Arceci, R. (2014, August 1). Thrombocytopenia-Absent Radius Syndrome: Background, Pathophysiology, Epidemiology. Retrieved September 23, 2015, from http://reference.medscape.com/article/959262-overview

[3] Brents, B. M. (2013). Comfortable seat belt extender that is easy to install and use: Google Patents.

[4] Meloul, R. (2004). Seat belt attachment to facilitate seat belt access: Google Patents.

[5] Federal Motor Vehicle Safety Standards and Regulations. (1999, March 1). Retrieved September 23, 2015, from http://www.nhtsa.gov/cars/rules/import/FMVSS/


We would like to acknowledge a number of people for their help in completing this project: National Science Foundation grant # CBET 3310005, Kevin Caves, Steven J. (Joe) Owen, Matt Brown, Steve Earp, Dr. Roger Nightingale, Lauren Zangari, John and His Family

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