One would imagine that taking a drive with Vaughan would be a dangerous proposition, although we know that his desire for theatricality probably excludes random acts of vehicular suicide.  Vaughan doesn't just have accidents, he plans them meticulously. 

When Ballard and Vaughan take to the road for an evenings drive, they discuss details of celebrity crashes, and the true nature of Vaughan's intentions and ambitions.  Vaughan drives his car lazily into a safety barrier, scaring it just as his body is scared.  His vehicle is a crash classic in the making, with every surface in some way damaged.

However, like any collector, only the real deal will do.  Vaughan enjoys his car, but his own fantasy is to drive an actual crash car, one in which celebrities have been injured or killed.  In some extraordinary dialog, he affirms that he see's the Kennedy assassination as a special kind of car crash. It's a fantasy that, strangely, he never gets to realize - yet he sets up for everyone else.  Vaughan is the star.

The dialog from this scene is worth repeating, as it explains Vaughan's obsession very well:

"VAUGHAN
I've always wanted to drive a crashed car.

JAMES
You could get your wish at any moment.

VAUGHAN
No, I mean a crash with a history. Camus' Facel Vega, or Nathaniel Nest's station wagon, Grace Kelly's Rover 3500. Fix it just enough to get it rolling. Don't clean it, don't touch anything else.

JAMES
Is that why you drive this car? I take it that you see Kennedy's assassination as a special kind of car-crash?

VAUGHAN
The case could be made."

This words are challenging, forcing the audience to face off with Vaughan’s oblique world view.  While Cronenberg had to remove references to living people within the film (most importantly Elizabeth Taylor, Vaughan's real obsession), this laundry list of past victims is daring indeed.  The allusion to Kennedy's death, a death that seems to haunt America, is an obtuse and fantastical reference, and illustrates how Vaughan see's all deaths in cars as some kind of vehicular murder, even if it involves a shooting.  Deaths both in and around cars are of equal importance. 

When the Ballard and Vaughan nearly collide with a cab, Vaughan playfully steers his car away from it, clearly not interested in this minor near miss (perhaps he’s simply playing with the more heightened sense of danger of his passenger).  He has other, more important ideas (one can safely assume they revolve around the Jane Mansfield recreation.)

During the drive, Ballard confesses that he's not sure why he finds all of this interesting.  He doesn't understand Vaughan's ambitions, what drives him.  It is sensible that he questions Vaughan on this, since Vaughan is the only one who has thought through the entire process.

The final reasoning from Vaughan is explained in this dialog:

"It's the future, Ballard, and you're already part of it. For the first time, a benevolent psychopathology beckons towards us. For example, the car crash is a fertilizing rather than a destructive event – a liberation of sexual energy that mediates the sexuality of those who have died with an intensity impossible in any other form. To fully understand that, and to live that... that is my project."

It is the very extremes that have brought Remington, Gabrielle, and indeed Vaughan together.  What excites Vaughan is a final event, a truly once in a lifetime experience.  It is his project, though others have started their own parallel travels. 

While the accidents might at first have appeared as random events, we hear now that Vaughan is articulate and focused, and that every moment of his accidents are planned.  Only the crumple zones, that random element of chance, injects any danger.  Vaughan is quickly working his way toward a frenzied climax.