专家仍然不清楚手机使用的安全极限是多少。

Experts cannot tell us a safe limit for cell phone use.

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当到达安全极限距离时，它能发出声光报警，提醒司机刹车。

If the distance is to be safe value limited, the device will give a sounding and light alarm to warn the driver braking.

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新制定的规章将修订运行和流程的安全极限以使之合乎标准，同时将对一系列的列车类型做详细解释。

The rulemaking would revise the safety limits for these operations and the processes to qualify them, and account for a range of vehicle types.

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