Safety shall be the first priority on transportation.
道路千万条,安全第一条.（“道路千万条,安全第一条”这种表达国内特有,所以直接翻译为“运输中安全第一位”）
Illegally refitted and overloaded vehicles are banned.
打击非法改装车辆,严禁超限超载运输.（非法改装和超载都可以用形容词结构表达,所以翻译为禁止非法改装和超载车辆）
Please do not take unauthorized commercial vehicles
非法营运车辆冲击营运市场,请勿乘坐 (直接翻译为“请勿乘坐未授权营运车辆”即可,因为这种车辆冲击营运市场,和消费者并无直接关系,消费者没心思关心)
Highway property and rights shall be guaranteed; and unauthorized excavation shall be cracked down.
保障路产路权,打击非法开挖.
Common facilities on roads shall be preserved to ensure your safety.
爱护道路公共设施,保障你我出行安全 (用目的状语to ensure来说明爱护道路公共设施对你我安全的重要性)
Building roads and bridges will benefit society,and transporting overloadedly will cause endless trouble.
修路架桥造福社会,超限超载贻害无穷.
本人精心翻译,请及时采纳哟,有疑问请交流.
