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A 4-wheel drive off-road vehicle was designed and fabricated using extensive hydraulic technology for the SAE (Society of Automotive Engineers) Mini-Baja competition. The vehicle incorporates an open hydrostatic transmission using a single pump and four independent drive motors. A constant power controller that maintains full engine power to drive the vehicle or stores excess energy in two accumulators controls the pump. Each of the drive motors is independently controlled using a proportional meter-out pressure control valve. The use of pressure control allows the flow to each of the motors to be proportioned based on the dynamics of the vehicle. A CAN bus controller is used in conjunction with a steering sensor to provide differential motor speed control in maneuvering conditions that insures 4-wheel drive availability at all times. Steering of the vehicle is achieved by articulating the chassis using a rotary actuator and multi-motion actuator controlled by the driver.

Speed-time data obtained in two large-scale studies by following randomly selected vehicles in a number of cities with an instrumented car are analyzed here by dividing the data into trip segments between successive stops and computing values of traffic variables for the individual trip segments. Results from the two studies are found to be in good agreement. The analysis focuses on variables previously shown to be related to fuel consumption, particularly on the relationship between energy used to accelerate the vehicle, energy dissipated in braking, and mean traffic speed. Braking and acceleration are found to play a major role in determining tractive energy requirements in low speed urban driving, since about half the energy supplied to the wheels is used to accelerate the vehicle, and about two-thirds of the resulting kinetic energy is dissipated in braking.

This study tested the hypothesis that seat belt usage is related to driver risk taking in car-following behavior. Individual vehicles on a Detroit area freeway were monitored to identify seat belt users and nonusers. Headways between successive vehicles in the traffic stream were also measured to provide a behavioral indicator of driver risk taking. Results showed that nonusers of seat belts tended to follow other vehicles closer than did users. Users were also less likely than nonusers to follow other vehicles at very short headways (one second or less). The implications of these findings for occupant safety in rear end collisions are discussed.