Phantom Hitchhikers,BVM apparitions and UFO encounters
A driver, usually alone, picks up a hitchhiker, who may be silent and uncommunicative or may make dire predictions of something bad about to happen. Shortly after the driver turns to look at the passenger and finds they have vanished unobserved from a moving vehicle. In some versions the hitchhiker is female, borrows or is lent a garment and gives the driver an address where they can collect the garment. When the driver calls at the address he is told the hitchhiker is dead, usually for years, and when shown the grave finds the garment they lent draped over the grave. In some variations the driver hits a pedestrian who promptly vanishes as the driver gets out of the car.
While much of this motif can be dismissed with some confidence as reworking and relocation of an urban legend the meme involved is not restricted to cars, goes back many centuries, with cases being reported in the New Testament, and some cases appear to be more than folklore.
Apparitions of the Virgin Mary are common enough to have their own abbreviation (BVM) and share common features with the Prophetic Phantom Hitchhiker and some accounts of encounters with occupants of UFOs.
These three phenomena share enough common features to be considered as aspects of a single phenomenon with similar if not identical origins.
The Phantom Hitchhiker
Roy Fulton was a normal guy, a carpet fitter with no interest in the paranormal. But the paranormal was about to take an interest in him. On his way home from a darts match he stopped to pick up a young man who was hitchhiking. A few minutes later he found the hitchhiker had vanished from the van while it was travelling at 45mph. He reported it to the police and they decided he HAD experienced something.
Goss investigated this story and concludes it most likely that Fulton did not fabricate the story and believed in his experience,
By definition Phantom Hitchhikers appear to drivers. In almost all cases the driver is alone and often at night. Driving, like computer programming, tends to induce an altered state of consciousness where the conscious brain automates routine tasks including attention to the road. It is possible in this state to enter a microsleep, if there is no potential danger, and experience a dream. It is tempting to conclude that this is what happened to Roy Fulton, possibly partly influenced by alcohol and therefore to class all such cases as dreams in microsleep. But we have no right to do so especially in the Fulton case. As a carpet fitter by trade his job was his driving licence: no licence, no job, so he was, we can infer, careful about his drinking and he admitted drinking only two pints of lager knowing that the local police clamped down hard on drunk driving. Also at that age most young men can drink a lot more than that and still be in touch with reality.
But we have at least a possible theory for some of those Phantom Hitchhiker cases that cannot be dismissed as tales relocated from elsewhere.
The BVM UFO connection
Phantom Hitchhikers are not always silent. Some talk. Some warn of potential disasters. Sometimes they are extremely local, warning of a road design hazard, sometimes they warn of an unspecified evil about to happen and sometimes prophesy specific disasters, which do not seem to come to pass.
These hitchhikers tend to manifest as mature females, tying in with the pagan concept of the Crone or a Jungian Wise Woman archetype. In 1975 several Italian motorists picked up an old woman who prophesied the destruction of Milan by an earthquake on the 27th of February. She then vanished and the disasters did not take place. In 1980 a series of Phantom Hitchhiker events involved a 50-60 year old woman who talked of God and salvation before vanishing, often from a fast moving car. The woman seemed concerned about a second eruption of the Mount St Helens volcano in Washington that year. This series is perhaps best put down as an urban legend with one accounts of the series involving an accurate prediction so precise, except for the year that it seems most likely to have been retrofitted to events, perhaps 24 years too late  .
The Prophetic Hitchhiker leads us naturally to the BVM and from there to UFOs
Apparitions of the BVM have been known for centuries. Typically a child or a poor peasant encounters a tall female who presents herself. Or is eventually identified as the mother of Jesus and ends to offer calls for prayer and penance to prevent a forthcoming war. After apparitions at Fatima, Portugal in 1917, the apparition told Sister Lucia de Santos that a pope would be shot. This prophecy was verified on May 13, 1981, when Pope John Paul II was shot in Rome but given the time lag is perhaps less impressive than it seems.
Irritatingly the BVM did not give advice to anyone in a position to influence events. Not even President George W Bush who claimed to get messages from God.
UFO contactees in the 1960s and later tended to receive warnings about impending nuclear disaster and a call for the world to change. These are generally on the lines of the warnings given in the Ashtar Galactic Command incident and reflect fears of nuclear disaster, perhaps fuelled by tensions between the USSR and the USA. The revelations to these contactees are not always so high minded. The author is still trying to relocate the source that told of early UFO contactees being informed that Mars was racially segregated with black and Jewish Martians kept separate from the white ones.
Putting things together
Any of the topics here could and have resulted in full length books of course.
Phantom Hitchhikers could be folklore relocated as needed, dreams caused by an induced altered state of consciousness with the experience either being archetypal or reflecting a folklore theme unconsciously remembered, genuine apparitions of deceased people or even, and there seems to be no investigation of this possibility, the Fairy folk playing tricks on humans. One argument against the dream explanation is the apparent absence of sexual relations between male drivers and young female hitchhikers, though the driver may well have had good reasons not to report this (while perhaps retracing the route in the hope of a replay)
The Prophetic Hitchhiker links neatly to those BVMs and UFO contacts calling for large scale changes in human behaviour to avert disasters including wars. The events these prophecies concern reflect common fears at the time and tend to evolve with time. At one time they involved wars, then nuclear wars and disasters and now they tend to warn of environmental catastrophe. Again it is possible that some BVM apparitions represent communication by some form of discarnate spirit or are dreams experienced in an altered state of consciousness or even Fairy manifestations (Lourdes has a long history of being associated with Fairies and some BVM encounters describe a tall woman dressed in white, matching the tall white aliens some UFO contactees describe.).
As always much more research is needed, and there is a need to develop criteria that can reliably distinguish between the various explanations of each of these phenomena and perhaps identify them all as having a common origin
Thus we need ground rules to tell us whether a Phantom Hitchhiker is relocated folklore, a genuine apparition, a dream, or something else. We need better criteria than the Catholic church provide for analysing and classifying BVM cases and good ways of distinguishing possible nuts and bolts UFO encounters from dreams, hallucinations or impersonation by spirits and the connection between UFO and Fairy lore needs to be investigated further.
https://en.wikipedia.org/wiki/Vanishing_hitchhiker Wikipedia article that seems to have been taken largely from Goss 
The evidence for Phantom HitchHikers, Michael Goss, Aquarian Press 1984.
http://www.mirror.co.uk/news/world-news/horrified-cabbies-pick-up-ghost-7293766 Post Tsunami Ghost passengers in Japan
Fortean Times 44 p.18 1985
http://www.catholic.org/mary/appear.php Catholic Online: Apparitions and Appearances
http://www.abc.net.au/radionational/programs/encounter/4812020 Why millions of Muslims are seeing apparitions of the Mother Mary
https://paranormallyperplexed.wordpress.com/2015/12/07/the-phantom-passenger-ghost-story-1/ Not quite a phantom Hitchhiker but an interesting case that could be related
http://weirdthings.com/2010/04/how-the-vanishing-hitchhiker-legend-attempted-to-thwart-hitler/ How the Vanishing Hitchhiker legend was used to try and thwart Hitler. This is too over the top to be believable and too over the top to omit.