Rik Nichol, 45, was driving under the bridge at Junction 5 going south on the M621 at around 7.15pm last night when the horrific incident occurred.
In footage captured by his dashcam, a figure can be seen moving across the bridge before launching the object - believed to be a small pipe - down at the vehicle.
Rik, who lived in Leeds for 40 years before moving to Wakefield, said: "It was approximately 7:15 last night.
"It was the bridge at junction 5 of the m621, I was heading south towards the m1.
"I have no idea what they threw but it hit really hard.
"It looks like a cylinder or small pole.
"The lad then ran across the bridge along turn stall road back towards Hunslet."
Rik posted the footage on a social media forum, where hundreds of residents vented their outrage.
Thankfully, Rik was able to manouvre off the carriageway and was not injured in the incident.