It happened on the B3081 near Verwood - he had to be cut free by firefighters.
Twitter Teenager Bailed After Warning
A 17-year-old youth arrested in Weymouth after a malicious tweet was sent to Olympic diver Tom Daley has been issued with a harassment warning.
Dorset police said the teenager was bailed pending an investigation into other communications on his Twitter account.
He was detained at a guesthouse in Weymouth on Tuesday 31st July - just hours after 18-year-old Daley received messages on the social networking site.
A spokesman for Dorset Police said:
''The 17-year-old arrested in the Weymouth area on suspicion of malicious communication has been issued with a harassment warning in connection to tweets to Olympic diver Tom Daley.
''In addition to the warning the teenager has been bailed to return to the police station at a later date whilst Dorset Police investigate other communications on his Twitter account.''
Daley and his Team GB diving partner, Southampton's Pete Waterfield, missed out on a medal yesterday when they finished fourth in the men's synchronised 10-metre platform diving event at the Olympics.
Shortly afterwards, Daley retweeted a message from a user which said:
''You let your dad down i hope you know that.''
Daley responded by tweeting: ''After giving it my all... you get idiots sending me this...''
Daley's father Rob died last year from brain cancer.
Tom Daley has been urged to take a two day break from Twitter after receiving the malicious messages.
British Olympic Association chef de mission Andy Hunt said Daley needed to make a decision over his use of the social-network website.
Press Association Sport understands Daley - who Hunt claimed received 50,000 tweets on the day of Friday's opening ceremony of London 2012 - will be advised to keep off Twitter two days before he competes in the individual version of his event on August 10.
Asked if the 18-year-old needed to stay away from the website from now until then, Hunt said today:
''That is absolutely something that the coaching team will discuss with Tom.
''They need to make the decision based on what they've experienced over the past 24 hours.
''Everyone knows if you use social media extensively, you have to accept you get bad as well as good.
''Sometimes bad is wholly unacceptable, as we experienced last night, and that's been dealt with by the relevant authorities.''
An apparent apology to Daley followed from @Rileyy_69 last night but it has been alleged he later posted an expletive-laden rant including a threat to ''drown'' Daley.
Hunt branded the @Rileyy_69 tweets - which the BOA said they had Twitter delete - as ''a threat'' but insisted Daley had not been affected by them.
''I've met this morning with Tom's coach and some of his other support staff,'' Hunt added.
''Tom isn't affected by it and the team are absolutely focused on getting ready for the next round of competition.''
Daley's synchro partner, Southampton's Peter Waterfield tweeted this yesterday:
''For all the haters out there, come do what we do then have ur say, Infact achieve what we do, low life pr''ck! Until then shut ur mouth! Tom done great it was my fault.''
Daley's close friend and Team GB diving team-mate Tonia Couch refused to be drawn today on whether the teenager should curtail his use of Twitter.
Couch, who also failed to win a medal in the women's synchro this afternoon in front of the watching Daley, said:
''Tom's a strong boy.
''He can concentrate on what he needs to do and, at the end of the day, Twitter's Twitter.
''You don't need to look at it if you don't want to.''
Asked what she made of the abuse Daley had suffered, Couch added:
''Not much really, neither has Tom.
''We're just concentrating on the Olympics. That's what we're here to do.''
Despite the abuse of Daley and the expulsion of two athletes from London 2012 for sending offensive tweets, Hunt insisted the BOA did not need to review their social-network guidelines.
They have largely left it up to individual sports and athletes when and how often they tweet, revealing today the women's water polo team had elected for a blanket ban, while hockey had a three-hour blackout around match time.
''We always said two year ago this was going to be the Twitter Games.''
Deputy Mayor of the Olympic Village Duncan Goodhew, a gold and bronze medallist in swimming at the Moscow Olympics in 1980, described the behaviour of the Twitter troll as ''appalling''.
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