BMX /Bicycling Case Study

Case Synopsis: A young boy on a BMX bicycle sustained injuries when he crashed while riding in an apartment complex driveway. It was alleged that the boy was riding over a bicycle-safe storm drain grate, but crashed due to a defective condition in and around the grate. Specifically, he testified that he coasted down a hill and, as he went over the area of the grate, his front wheel suddenly became trapped and he was thrown over the bars. The defective condition included pitting of pavement creating a “pothole” in front of the leading edge of the drain, as well as deformation of the grate itself.

Expert Analysis: A site inspection was performed at which time three-dimensional High-Definition Survey (HDS) laser scans were taken of the deformed storm drain grate, the freshly patched pavement around the storm drain, and the downhill path leading to the storm drain. Scene photographs from the time of the incident were analyzed, along with the three-dimensional laser measurements to create an accurate, to-scale computer model of the pavement and storm drain condition, as it had previously existed. An exemplar BMX bicycle was inspected and measurements were utilized to create a to-scale computer model of the BMX tire.

An analysis of the geometry of the roadway and the bicycle tire established that the tire would dip a limited distance downward as it traveled over the pavement condition in front of the drain, and even less distance down into any location on the grate itself. Calculations and testing established that, for the bike speeds under consideration, the bicycle would simply roll over the irregularities in the storm drain area and there would not be sufficient rearward forces on the bicycle tire to result in the pitch-over bicycle dynamics described in this case. The specific testimony as to how the incident occurred was shown to be inconsistent with the laws of physics.

Result: Case settled.