How does the author convey that the car's driver is drunk in The Great Gatsby?

It is a dissolute crowd, Nick learns, who attend the elaborate parties of Jay Gatsby, parties that, oddly enough, he does not attend. At these parties where no one really knows anyone else, the conversation at times revolves around the host. 

"Somebody told me they thought he killed a man once."

"I don't think it's so much that...it's more that he was a German spy during the war."

Another man assured the other guests that a man he knows grew up with him in Germany. Then, someone else says Gatsby killed a man. All of these speculations increase the romantic mystery about him. 

Later, other people are "brought in" and the rumors about Gatsby continue. Finally, Nick unknowingly talks with Gatsby, who invites him to join him in a hydroplane the next day. After Gatsby confers privately with Jordan Baker, she and Nick depart. As they walk down the steps, Nick observes that a car is in the ditch beside the road with a wheel "violently shorn." Adding to the confusion of the scene a man wearing a duster stands amazed, "See!...It went in the ditch." Nick narrates,

The fact was infinitely astonishing to him--and I recognized first the unusual quality of wonder and then the man--it was the late patron of Gatsby's library.

Earlier, Nick has talked with this man, whom he has met in the library in a drunken state--Owl Eyes himself has said,"I've been drunk for about a week now, and I thought it might sober me up to sit in a library." However, he claims he was not driving. Then, gradually "a pale dangling individual steps out of the wreck, pawing tentatively at the ground with a large undercertain dancing show."

He is blinded by the headlights' glare and is confused blaring of the horns of other automobiles. That he is drunk is evinced by his speech:

"Wha's matter?....Did we run outa gas?"....
At first I din' notice we'd stopped."
Wonder'ff tell me where there's gas'line station?"

As proof that he is drunk, he asks someone to put the car in reverse when the wheel is completely separated from the car.