请上车的英文表达是 "please board the train/bus/vehicle". 来源可能源于交通工具的乘客上下车时，工作人员会叫喊这句话来提醒乘客上车。例句：

Please board the train at platform 2. (请在2号站台上车)

The bus will leave in 5 minutes. Please board now. (巴士将在5分钟后开走，请现在上车)

The vehicle is ready to depart. Please board quickly. (车辆即将出发，请快上车)