This could be a real downer if the driver is unable to maintain control of the vehicle. It also is a possibility that the driver doesn't have a license or is driving a stolen vehicle. Don't forget some drivers like to show off because they have a captive audience. There's also a chance that after reaching your destination the driver will take off with your belongings neatly packed in the vehicle's trunk. These are just a few of the hazards hitchhikers face.
Drivers picking up strangers face similar risks.
It is quite possible that a hitchhiker will get a ride from a decent human being and the trip will prove uneventful. Remember, however, you may be betting with your life for such an uneventful cruise down the highway.