Lineriders cars have been designed by Philip Worthington and William Denniss to follow lines that people draw on the surface with pens, speeding up and slowing down according to a visual annotation language. The toy car is equipped with sensors that allow it to follow the lines. the track can be annotated with symbols that are understood optically by the car, telling it to alter it’s driving pattern (eg. speeding up for a jump, slowing down or preparing for an oncoming obstacle or sharp turn). Link.