Richard Rawlings has to deliver his grandson yesterday when his teenage daughter went into labour by the side of the road in a snow storm.
Richard, 39, was driving to get Jade, 17, to hospital but baby Caleb couldn't wait.
Mr Rawlings quickly pulled over by the roadside in the blizzard, and with the help of 999 ambulance operator Gail Bartlett, helped deliver the healthy 7lb 2oz boy.
Mr Rawlings, from Tilehurst, Reading, said: "It was all so fast."
Proud father Jonathan Cooke, 20, who works in a warehouse and was also in the Ford Mondeo, said: "I am over the moon. It was scary."
Last night new mother Jade and baby Caleb were doing well. A spokesman for South Central Ambulance Service said: "Gail could clearly hear the first cry of the baby boy."
More speedy snow delivery stories here:
Neighbour delivers baby in snow storm