The car was in fourth gear.

那辆汽车处于第4挡。

《柯林斯英汉双解大词典》

You may want to turn off the speed control in hilly terrain if unnecessary shifting between third and fourth gear occurs. Unnecessary shifting of this type could result in reduced fuel economy.

在多坡地形行驶时，如果出现不必要的第三档和第四档之间的换档情况，而你可能还要关闭定速巡航功能，这种没有必要的切换形式会导致燃油经济性的降低。

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I noticed that she was keeping the car in second gear when she clearly should have shifted to third, maybe even to fourth. Stupidly, I told her so.

我注意到她打在二档上，通常这种状况应是三档或四档，于是我告诉她该如此如此。

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Fourth gear, the bills: at the moment, electric car ownership is encouraged with tax breaks.

BBC: Promise, but daunting challenges for electric cars

As he reached the brow of the hill, Ramshaw said he had just gone into fourth gear but was not driving fast.

BBC: NEWS | UK | Wales | South East Wales | Crash driver 'felt pressurised'

But they may have to shift into fifth or at least fourth gear instead of the usual second gear of the Chinese government.

FORBES: China Official Warns Of Tough Months Ahead For Exporters