Roads chiefs say the A41 was gritted the night before three accidents forced police to close the dual carriageway between the M25 and Berkhamsted.
The first single-vehicle smash paramedics were called to was in Kings Langley at 7.45am yesterday, and a second in the same place happened just under 40 minutes later.
The driver of the first accident was being assessed in an ambulance as the second one happened.
East of England Ambulance Service spokesman Richard Dunne said: “While we were there, another crash happened. A car went up a bank off the road.”
A paramedic fast response car was sent to the Felden stretch of the A41 just after 9.45am to help a motorcyclist who had slid on the ice.
At that stage police decided to close the dual carriageway as a precautionary measure, but they were unable to give details of how long it remained closed.
Herts County Council spokesman Simon Hoggett said: “We did do a gritting run on Saturday night, and the A41 was salted and gritted as part of that.”