Well, for what it's worth, I think it is common knowledge among the BJ bikers that it is possible to go on the expressways and that is the normal way to get out of the city. We pay just like cars and only once I got a surprised look from one of the tollgate clerks. I don't know where I read it but I have this fixed idea in my mind that this is true for BJ and Tianjin.

And btw: We rode two up on the BJ expressways many times...