It is often necessary in a film narrative to move in a linear fashion toward a conclusion.  Reflection on past events are not easily dealt with, usually reduced to facial expressions, reminiscing conversation, blank stares at old documents, objects, voiceover, or flashbacks.  The novel doesn't have these visual or narrative restrictions, opening the palette for the author to take as much time as necessary to investigate not only an event, but the ripples the event sends through the lives of those affected.

Ballard has just been through two major events, the taking of LSD, and making love with Vaughan.  The residue of the drugs, their lingering effect, gives Ballard time and space to re-experience his actions.  Sitting at home, anchored in a chair overlooking the roadways and parking lot, Ballard reflects upon events, mothered in the background by Catherine. 

With the omission of the drug episode from the movie version, Cronenberg instead skips the self-analysis and moves quickly onto the attack on Catherine's car.  While pushing the story forward, this quickening of pace, while losing some of the fall out from the sexual experience, will likely cause some issues for those trying to decipher the motives and emotional impacts for the central characters in the movie.  To truly gain an understanding of the final scenes, one needs to appreciate that the coming together of Ballard and Vaughan isn't simply another sexual event, but instead has a deeper psychological impact. 

Locations have also been subtly changed, so for instance, in the novel Catherine's car is visible from the balcony of the Ballard's apartment:  "Catherine's car sat in the drive below the bedroom window."  In the movie adaptation Ballard's apartment is situated high above a freeway.  In order to see the damage to the car Catherine has to tell her husband about it, and he must travel down to the parking spaces in the basement. 

Tiny details, not significant in any creative way, also change.  For instance, the damage to Catherine's car is moved:  "The paintwork along the left hand side had been marked in some minor collision."  In the movie adaptation this is moved to the right hand side.  This is probably due to the fact that the novel is set in the United Kingdom, with the driver seated on the right of the car, whereas in Canada - where the film was shot - the driver sits on the opposite side.

Once again the novel reminds us that parallels, dreams, and free-association are more readily achieved within the context of the written word.  As Ballard runs his hand along the new junctures of the damaged car panels, we can only speculate within the movie what is going through his mind.  In the novel the author makes it clear that Ballard sees within the dents and scratches pieces of Vaughan, sexual organs, dreamscapes of their having come together.

It is at this point that Ballard suggests to Catherine that they go for a drive.  The climax to the story is quickly unfolding, and Ballard knows that it will enact itself on the road.  The damage to Catherine's car is part of Vaughan's courtship of Ballard's wife, yet it seems obvious that he wouldn't follow any traditional path to seduction.  Vaughan's love making is almost entirely based around past events that have occurred on or around traffic systems, so if he is to have Catherine, then she must join him on the highway.  If Ballard is to taunt Vaughan, then the only venue it can have a meaningful effect is by getting into the car and hitting the road.

Once they are on the road Ballard suffers a bout of clarity, with storefronts coming into stark relief, and Catherine herself taking on another level of reality.  His wife grows nervous, realizing that something monumental is approaching.  This dialog also appears within the movie, however Cronenberg omits a single line with acts as something as a coda.

The novel expresses the conversation thus:

'The traffic-where is everyone?  'They've all gone away.'

'I'd like to go back-James!'

'Not yet-it's only beginning . . .'

Deborah Unger's portrayal of Catherine, ethereal, dreamlike, doesn't allow for surface drama that demands an exclamation point.  Instead she delivers her line in a flat non-committal way. 

The addition of the final line within the novel changes things considerably.

It is clear when this line is spoken that Ballard knows what will follow, and that he is simply waiting for events to play out.  Within the film Cronenberg maintains an element of mystery.  When Vaughan meets his end Ballard and Catherine are shown to be somewhat surprised.  In the movie the audience is left to guess, to wonder exactly what is going on.  The additional line in the novel tips us off that Ballard is aware that he has a specific role to play in what will follow, even if he isn't aware of the details.

The drive to the next checkpoint in the novel is also vastly expanded.  The movie uses the drive to provide a final joust between Ballard and Vaughan, but the novel is far more self-reflective.  For example, Ballard revisits the underpass location where he had made love with Vaughan.  While Catherine was not aware of it, Ballard stops the car and poses as Vaughan just before he was sodomized.  To ensure we don't misunderstand the events that had taken place JG Ballard makes it clear for us:  "By some paradox, this sex act between us had been devoid of all sexuality."  The film version has always struggled against the easy interpretation that it's essentially a movie about sexual perverts, a subverted soft-core sex film.  With this single line we are alerted to what should have been obvious to everyone - Crash does a lot of things, but it never titillates.

Still, Cronenberg is to be commended for resisting the temptation to spell out the motives and actions for the narrative illiterate.  JG Ballard includes additional dialog that seems superfluous and a little too explanatory:

'Are you looking for Vaughan?' Catherine asked.

'In a manner of speaking.'

'You're no longer frightened of him.'

'Are you?'

'He's going to kill himself.'

'I knew that after Seagrave died.'

Cronenberg chooses to deny us this text, leaving us to determine just what Ballard and Catherine are thinking and doing on the highway.  Interestingly, in both cases, Vaughan is very much in the scene with them without (up to this point) actually appearing. 

Largely, Vera Seagrave is very much marginalized in the movie.  In cropping the novel of its more superfluous material, cutting to the core of the message, there is little room for Vera and her actions.  We see her only fleetingly, and then only because events must take place within Seagraves's apartment.  There is little for her to do.  After the death of her husband she disappears completely.

While this is understandable, it also leaves us with unanswered questions.

What happened to Vera after the death of her husband (not forgetting that in the novel the Seagraves had children)?  What does this woman actually do?  What is she really like? 

The novel can help us fill in these blanks by giving her a final bow.

Ballard and Catherine find Vera at a gas station, stopping to have a few lines of dialog:

'Are you leaving?' I pointed to the suitcases in the rear seat of Vera's car. 'I'm trying to find Vaughan.'

'He's following his film actress. The police are after him-an American serviceman was killed on the Northolt overpass.'

I [Ballard] put my hand on the windshield, but she switched on the windshield wipers, almost cutting the knuckle of my wrist.

Explaining everything, she said: 'I was with him in the car.'

So Vera and Vaughan had continued their relationship, and had even taken to killing pedestrians.  Vera was on the run, knowing she'd finally be caught if she stayed, Vaughan was still lost.

It is moments such as this, when comparing the novel with the movie, that we gain the most delight.  Gaps in the film can be filled, questions and motivations answered.  Ciphers become full and some of the dark corners of mystery are shown in full light.  It's startling that Vera had been party to the death of a man, but it's good to have some kind of closure.  At the same time, we are also alerted to the fact that Vaughan has taken a new turn, now openly killing with his vehicle, and that he is actively being pursued by the authorities. 

Such obvious challenges to conventional thinking, the use of a car as homicidal entertainment, would have presented a blatant attack on censors everywhere, and Cronenberg, already no doubt aware his film would have challenges, correctly avoids the issue entirely.

At times the final scenes of the movie version feel somewhat rushed.  In the novel however the author takes time to let events mature, putting off the inevitable ending until the last possible moment. 

Days pass, and in this time span Catherine takes to the road going to and from work, followed at all times by Vaughan.  Ballard follows along, observing this obscure mating ritual from a distance.  Vera calls Ballard to see if he has found Vaughan, but he lies and says he has not.  The police have raided her home and removed Vaughan's pictures.  The police make only one brief appearance in the movie, and then it's only to ask about a dead pedestrian, an accusation Ballard mocks.

Finally Vaughan abandons his car, its interior smashed and covered in the remnants of its tenant.  In the movie Vaughan's car becomes a crash vehicle itself, a celebrity monument that Ballard inherits and uses to consummate his Crash relationship with his wife.  In the novel the car merely fades away, brutalized, tired, and dead before even Vaughan.  Having been his obedient servant, it finally gives up as tires deflate.

Still, Vaughan needs a car, so in his final coming together he steals Ballard's car from the parking garage.  As he races away from the apartment building he narrowly misses Catherine as she surveys Vaughan's wreck.  The next time they see the car it is destroyed.