双面黄色木板有两侧的两个垂直红黄色闪烁灯，另一侧有两个黄色闪烁灯，用于表示工作现场（When a section of track is required for maintenance and trains cannot run, it is handed over by the operators to the engineers, who take "possession". Special protective measures are used to prevent access by unauthorised trains. When the track is returned to the operators, the engineers "give up possession".
" class="glossaryLink ">拥有）。有两种类型：（i）占有（红灯）（ii）工作现场（黄灯）。拥有和工作现场不一定是一样的。
