In this project, single bicycle crashes have been simulated at the VTI crash safety laboratory. Two different scenarios have been replicated: 1. A sudden stop, likewise representing something getting stuck in the front wheel (shopping bag, an object getting stuck in the front wheel or a too efficient handbrake) or hitting something solid un-yielding. 2. A sideways dislocation of the front wheel, representing hitting a curb stone from an angle or the loss of friction sideways due to icy winter conditions. Crash tests were performed using a Hybrid II 50 percentile crash test dummy riding four different types of bicycles: * An open frame bicycle with an upright seating position, often referred to as a lady’s bicycle. * A closed frame bicycle with a more prone seating position. Can be referred to as a man’s bicycle or a more race-like bicycle model, with a seating position leaning forward over the handle bars. Can also be referred to as a commuter bicycle. * A recumbent bicycle, with a more or less lying down seating position. * A rather standardized closed frame bicycle with an additional electric support engine enclosed in the front wheel hub and a battery positioned in the lower cross member of the frame. Can be referred to as a pedelec with a seating position mainly upright, resembling to the first open frame bicycle. There is a variation in respect of seating height, seating position, and distribution of weight between the various bicycle types included in the project. The objective was to study head impact related to the influence of these factors in given and controlled single bicycle crash scenarios. On a longer term, the goal is to attain knowledge about effective bicycle design features to diminish the injury outcome of single bicycle crashes. An important objective was also to examine the possibility of using crash tests to study single bicycle crashes and to identify potential improvements of the method. Each bicycle type and crash scenario have been controlled at two different speeds, 15 and 25 km/h. As a reference, overturning has been done with a freestanding bicycle, not in motion, which equals a purely sideways fall of the bicycle with a dummy bicyclist in the saddle at 0 km/h. Repeated tests were performed to further investigate the repeatability of the chosen method, as similar crash tests have not been done earlier. The repeatability can be questioned, since minor changes in dummy placement and performance obviously affects the free rolling behaviour of the bicycle and subsequently the motion when crashing and falling. In addition to acceleration measurements in the crash test dummy head, filming has been done with both video- and high speed video cameras to be able to study the falling motion in detail. The actual dummy head has also been smeared in red paint to make it possible to detect areas of head impact as well as the distance on the floor where the head hits ground. About 30 pre-tests had to be run to modify the bicycle propulsion system and finalize a test procedure judged to give reasonable repeatability. After that, almost 40 simulations of bicycle crashes in motion were performed and 20 sideway falls with a bicycle standing still. The following bullet points can summarize the results: * When falling sideways on a bicycle standing still, the seating height might influence the head impact. * A sudden stop will result in a falling motion over the handle bars causing a forceful head impact while a sideways dislocation of the front wheel will result in a falling motion to the side causing a more moderate head impact. * A higher speed can result in a more forceful head impact. * The falling pattern varies between the different bicycle types depending on crash test scenario and speed. * The open frame lady’s bicycle results mainly in a falling pattern where hip and shoulder hits the ground just before the head, at least at lower speeds. * The closed frame commuter bicycle, where a cyclist has a prone forward seating position, will in most cases result in the head taking the initial hit at the ground. This is especially obvious at higher speeds. * In the executed tests, there is no evidence that the pedelec produces any enhanced risk. On the contrary, it seems that the sheer extra weight and low centre of gravity reduces the risk of a head-on dive over the bicycle handle bars. * The recumbent bicycle did just tip over sideways at lower speeds. But at higher speed and with the sudden stop situation, the recumbent bicycle did, for some of the cases reproduced, show a risky behaviour of tipping over the front wheel, sending the crash test dummy in a dangerous high arc just as risky or maybe even more risky than for all the other bicycle types. An overall impression of the crash tests performed, is that they are very sensitive to minor adjustments and therefore it is difficult to achieve a high repeatability. Even slight changes in steering angle or dummy seating position made a considerable difference. For the sudden stop situation, a straight handle bar and straight front wheel easily did tip the dummy over the front wheel, while the slightest steering angle change (sometimes made by the dummy while leaving the carrier test sled) resulted in a sideway falling motion. This is probably also true for real-world bicycle crashes, since even small differences in the bicyclist behaviour in the beginning of a crash situation will make a huge difference in the accident outcome. A human bicyclist has an entirely different possibility to adapt in a crash situation and as well use hands, arms and body to protect him/herself, given that a fall is induced. (Author/publisher)
Samenvatting