According to the Consumer Products Safety Commission (CPSC), there are approximately 10,000 golf car related injuries requiring emergency room treatment in the US each year. One significant mode of injury in golf car accidents is passenger ejection, which can lead to serious injuries, especially of the head. Based on CPSC statistics, roughly 35% of golf car accidents involve a person falling out of the car. In addition to ejection accidents, at least 10% of golf car accidents involve a rollover and statistics indicate that such accidents are roughly twice as likely to lead to injuries requiring a hospital stay as non-rollover accidents.
Passenger Ejections
One common scenario for a passenger ejection accident occurs when a car, traveling near its maximum speed, is turned sharply to the left. During a sharp left turn, centrifugal acceleration forces tend to force the passenger to his right, which can lead to ejection. Sharp turns are less likely to lead to a driver ejection because the driver has a steering wheel to hold onto and can always anticipate when he is about to initiate a turn.
Golf cars are typically not equipped with seatbelts because of their need to allow passengers to enter and exit the vehicle frequently with ease. Therefore, the ANSI (American National Standards Institute) golf car safety standard, Z130.1, does not require seatbelts for golf cars. As a result, it is prudent to equip golf cars with passive restraints that will protect unbelted passengers from ejection. In place of seatbelts, golf car standards require readily accessible handholds and body restraints that prevent the occupants from sliding to the outside of the vehicle.
As a result, golf cars are typically designed with rectangular or semicircular bars that rise up from each side of the car's bench seat and are designed to serve as both handholds and hip restraints. One of the deficiencies of this design is that the location of the handhold (i.e. at the outboard edge of the seat) is also the fulcrum about which an ejected passenger will tend to rotate. Therefore, this type of handhold, even when used, does not provide the passenger sufficient leverage to prevent ejection. Another possible deficiency is that the side restraint may not be large enough to prevent ejections.
Technology Associates has performed biomechanical simulations of golf car passenger ejections using the Articulated Total Body (ATB) software to evaluate the effectiveness of existing hip restraints. This research indicates that many of the hip restraint configurations currently installed on golf cars, which are typically 3-4� tall, are not adequate to prevent passenger ejection during a sharp turn at high speed. However, restraint design improvements can be easily made that will greatly reduce the likelihood of passenger ejection without interfering with convenient entry and exit from the passenger side of the seat.
Rollovers
Rollovers often occur as a result of a driver losing control of the car while traveling downhill on a car path. One potential source of a downhill loss of control is the current industry practice of manufacturing golf cars with brakes on only the rear axle wheels. It has long been understood that a braked vehicle with skidding rear tires and rolling front tires is directionally unstable but this instability will not always manifest itself when a vehicle is traveling at sufficiently low speeds on level ground. However, besides reducing braking effectiveness (when compared to four wheel braking), rear wheel only brake designs can easily lead to �fishtailing.� Furthermore, the reduced braking effectiveness on downhill slopes can lead the driver to falsely perceive a brake failure, causing him to press harder on the brake pedal, which in turn leads to a locking of the braked wheels and an out-of-control skid. This hazard is aggravated at golf courses that incorporate hilly terrain with steep, narrow golf car paths and sharp turns. Such conditions make it desirable to create golf cars with good braking characteristics for use on courses with downhill slopes of 10 degrees or more.
Industry standards for the design of golf cars contain minimal braking requirements that do not include tests for downhill braking. In addition, there are no widely accepted standards for golf car path design, and inadequate recommendations provided by car manufacturers for maximum path slope and minimum turning radii are ambiguous with warnings that refer to �steep grades� and �sharp turns� without quantifying these terms. This separation between golf car design standards, which only require dynamic braking tests on flat ground, and sloped car path design, which lack any specificity, causes golf cars to be routinely driven on potentially dangerous terrain that is not addressed by the ANSI golf car standard. In addition, while the ANSI standard requires that a golf car's maximum speed not exceed 15 mph on level ground, that speed can easily be exceeded when traveling downhill.
To evaluate the potential hazards of creating golf cars equipped with brakes on only the rear axle wheels, Technology Associates has analyzed the braking of a two-axle vehicle, equipped with brakes on either or both of its axle wheels. In addition, dynamic two-dimensional simulations of a braking golf car traveling downhill have been created to study vehicle dynamic stability. For this comparison, we introduce the term �braking efficiency�, defined as the actual vehicle braking deceleration, divided by the braking deceleration of the same vehicle with brakes on all four wheels (i.e. the maximum possible braking deceleration for a given slope and coefficient of friction). Thus, by definition, the case with braking on all four wheels yields an efficiency of 100%.
For either case where only the front or rear wheels are braked hard, braking efficiency decreases rapidly as the downhill slope increases, such that at path down slopes over 20 degrees, the brakes are no longer able to prevent the golf car from accelerating downhill. For slopes of 10-15 degrees, with which golf cars must currently contend, placing brakes on only the rear axle wheels provides only 25-37% of the braking that could be achieved with brakes on all four wheels. Therefore, equipping a car with brakes on only the rear wheels reduces the available braking efficiency significantly when compared to a vehicle with brakes on all four wheels.
Dynamic simulations indicate that golf car yaw instability is not likely on flat ground and will not manifest itself during ANSI brake performance testing. However, for a vehicle with brakes on the rear wheels only, when the initial speed is 17 mph or higher, yaw instability can occur when traveling down a 10 degree slope when modest steering inputs are made. Such loss of control could easily cause the car to leave the path and either collide with, or tip over, nearby obstacles and path curbs. However, when the front axle wheels, or all four wheels, are braked hard enough to lock them, there is no significant deviation from straight path travel. Therefore, if the cars were equipped with front brakes (either by themselves only, or in combination with rear brakes) this yaw instability problem would be significantly reduced if not entirely eliminated.
Kristopher J. Seluga, PE, is a Mechanical Engineering, Accident Reconstruction, Biomechanics, and Safety Expert with over 20 years of experience. He received his Bachelor's and Master's degrees from the Mechanical Engineering department at MIT where he worked on the development of novel three-dimensional printing technologies. Mr. Seluga is also a licensed Professional Engineer in New York and Connecticut, and has served as a member of the ANSI engineering committee for the Z130.1 and Z135 standards for golf cars and PTV's. His research interests and peer reviewed publications span the topics of Motor Vehicle Dynamics, Product Safety, and Biomechanics.
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