Twenty-eight-year-old Anthony Sanders was on the A331 dual carriageway on Boxing Day when the object was dropped as he approached the bridge just past the North Camp slip road heading towards Aldershot.
Mr Sanders swerved into the central reservation, completely writing off his six-year-old Saab convertible.
“My first thought was that’s it — I’m dead,” he said. “I was worried the car would flip over, and I wasn’t sure how strong the roof would be as it’s a convertible.”
Mr Sanders smashed into the barrier at around 60mph, causing it extensive damage, although he miraculously escaped with only bruises.
“I was extremely lucky,” he admitted. “I’m very glad that no-one was coming up behind me at the time.
“I had been in the process of overtaking a car on the inside lane when I saw two people on the bridge above and they threw something towards me.
“I thought I was going to hit the other car if I moved to my left, so in trying to miss it I completely oversteered and hit the central reservation.”
The front of Mr Sanders’ car caved in when it hit the barrier, and the driver he had been overtaking stopped to try to help him.
“I think the other driver was as shocked as I was to see that I was actually alright,” said Mr Sanders, who lives in Essex.
“The car definitely didn’t look good.”
A motorist on the opposite carriageway saw what happened and spotted two youths on the footbridge above the road. He immediately stopped his car and sped up the bridge to catch them.
Two youths were later arrested by Farnborough police. The pair, who cannot be named for legal reasons, have both been interviewed and are on police bail.
Investigating officer Pc Mark Chapman said: “This was extremely dangerous and frightening for Mr Sanders.
“It is very similar to an incident on the M3 around five years ago that nearly killed a driver, when youths threw a concrete block off a bridge on to his car.”
Pc Chapman would like to speak to any motorist who saw people on the bridge between Aldershot and North Camp that day.
He can be contacted at Farnborough police station on 0845 0454545.