这个标识代表什么意思?What does this sign mean?

这个标识代表什么意思?What does this sign mean?
前方有事故,以不超过50公里的时速行驶Drive no faster than 50km/h because there's an accident ahead
前方有事故,降低行驶速度到20公里/小时Drive no faster than 20km/h as there's an accident ahead
停车,等待工作人员移除这个标识Stop until someone removes the sign
这个标识无效,道路交通事故标识应该是蓝底白字的This sign isn't valid - they're only ever in blue with white writing

不管是蓝底白字还是黄底黑字,只要有ACCIDENT的字样就应该把车速降到21公里/小时