Brian Hampton, from Kent, has been jailed for six years over the death of Jade Clark on A31 in Ringwood.
He knocked the teenager off her moped and tried to cover up his crime.
Sentencing him at Bournemouth Crown Court Judge Wiggs told him: "You killed a young girl who was driving her moped.
"You were very fortunate not to be charged with causing death by careless driving.
"It could be argued that your driving fell far below the standards of a competent and careful driver.
"This is a bad case of causing death by careless driving."
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The M20 London bound carriageway has now been reopened to traffic but Operation Stack is expected to remain in place into the weekend.
Friday morning's forecast for the east of the region
Friday morning's forecast for the west of the region