The wavespeed. The valid range is 0 to ·. The range is 0 to 1. The default is 1.
波纹的速度，有效范围是从0到无穷大，滑块范围是0到1，缺省为1。
3
It is showed that a shock wavespeed distribution in red light period at a plane intersection satisfies a normal assumption, as well as Poisson assumption.