It happened on the B3081 near Verwood - he had to be cut free by firefighters.
Hunt For Sex Attacker In Bournemouth
Police believe a man thought to be responsible for two sexual offences could be behind other similar crimes that have all taken place in the past year.
Officers in Bournemouth have made a fresh appeal for information a year after the first of 12 unsolved sex offences took place in the city.
Detectives with Dorset Police said that two of the attacks are definitely linked, adding they are keeping an "open mind" over the other ten, despite no "clear" indication of a link.
The offences took place in Bournemouth, Dorset, between January and November 2011.
Bournemouth CID, assisted by Safer Neighbourhood Teams, said they are continuing to investigate the "distressing incidents" with house-to-house inquires this week.
Detective Inspector Steve Thorpe, of Bournemouth CID, said:
"Over the past year we have released numerous e-fits, descriptions and a CCTV image in hope that members of the public may be able to provide us with vital information about these offences.
"Extensive inquiries confirmed that an indecent exposure offence in January and a sexual assault in late May are connected and it may be that this man is also involved in other reported crimes.
"We are keeping an open mind, however it must be stressed that there is currently no clear indication any further offences are linked.
"We are determined that the victims will see justice done and that any person or people responsible for any number of these upsetting crimes is brought before a court as soon as possible."
Police received reports of around 12 similar offences in the Alum Chine and town centre areas. Forensic evidence confirms that the same offender is responsible for at least two of these crimes, police said.
In one incident a woman was dragged into a driveway and sexually assaulted.
In another incident a 19-year-old woman was inappropriately touched by a man as she walked along a road.
There have also been a number of incidents where a man has indecently exposed himself.
Violent crime was up 37% in the last year. Police say it's mainly due to a change in how offences are recorded.
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