欢迎乘坐我们的出租车！is an idiomatic Chinese sentence. When a passenger enters a taxi, the driver can use it as a greeting. By word-for-word translation,
欢迎: welcome (to)
To make it a sentence: Welcome to take our taxi!. But from the English perspective, Welcome to take our taxi! is a wrong sentence. So, I have some difficulty to turn that Chinese sentence into English.
By the way, some cabs in Shanghai have a machine installed. When a customer enters the car, it will play the utterance: Welcome to take our taxi!. It just sounds ugly to an English native's ear.