It would mean "driving like a maniac":
This is from an article headlined BOBBI KRISTINA'S BF
Terror Behind the Wheel:
"Bobbi Kristina's boyfriend Nick Gordon was arrested for driving like a maniac last night ... hours after Whitney Houston's daughter totaled a Chevy Camaro in a frightening wreck of her own."
Another article sports the headline: MIRANDA COSGROVE: TRUSTED MOTORIST OR TERROR BEHIND THE WHEEL?, so a terror behind a wheel is definitely not a trusted motorist or careful driver.
On Yahoo Answers, the question "Are you a good driver?" elicits one answer "Well no..I am a terror behind the wheel..nobody lets me drive..it boggles my mind.."
EDIT: I have found no mention of competitive driving. The sequence is also occasionally used in relation with terrorist attacks, but not as a noun phrase like this. Instead you will find something along the lines of a ride of terror behind the wheel, where terror is not the head of the phrase.