Connolly's near-fatal accident occurred in May near Flagstaff, Ariz., while filming a 2,488-mile trek across the iconic American road on a two-seater trike, Ireland's rte.ie reported.
He had just wrapped up the four-part series for Britain's ITV and was attempting to ride the trike onto a flatbed trailer when things went pear shaped, contactmusic.com reported Thursday.
"We came to the end of Route 66 and there was a [steep incline] with gravel. My bike has got three wheels and I went up and round. I was using cruise control on the throttle and it jammed on and I slipped the clutch. The trike came over on top of me and broke my rib."
"There is a button on the vehicle to boost its power, and Billy reckons his glove might have accidentally triggered it," an unnamed show insider told Britain's express.co.uk.
Connolly, 68, was taken to a Flagstaff hospital for treatment. He left with material for a future act.
"I've got a rather glamorous purple patch on my knee which you will only see when I wear my kilt. I will lie about it -- goddamn those Germans and their shrapnel," Connolly told the dailyrecord.co.uk.
Billy Connolly's Route 66 will air only in Britain on ITV next month.