众所周知，交通信号灯(traffic lights/ traffic signals)有“红灯停，绿灯行(The green light allows traffic to proceed. The red signal prohibits any traffic from proceeding.)”之说。

[SIPA]

“开绿灯”指交通路口打开准许行人车辆通过的信号(give the go-ahead signal，give the green light)，后多用于比喻“允许某事(allow someone to do something or something to happen)”，或“提供方便条件(make easier for)”。

例句：

官僚主义总是为腐败大开绿灯。

Bureaucracy always gives the green light to corruption.

我们永远不会给赌博开绿灯。

We'll never give the green light to gambling.