The A41 has now been completely reopened after a multi-vehicle collision during a sudden hailstorm forced police to close the dual carriageway completely earlier today.
Firefighters were called to the Bourne End junction of the road just after 11.45am, but it was later discovered that the smash happened closer to the Hemel Hempstead junction.
Eye-witness Adam Martin wrote on social networking site Twitter: “Just seen the biggest pile up I’ve ever seen on the A41... at least seven/eight cars spangled!”
A string of fire engines rushed to the scene, but they left after an hour when it was realised that they were not required. Police were forced to close the dual carriageway for about two hours.
An air ambulance was called out after early reports to the police suggested that about nine cars were involved in the collision.
East of England Ambulance Service spokesman Sophie Taylor said four people suffered neck and back injuries but that their injuries did not appear to be life-threatening. Three of them were taken to Watford General Hospital.
Two fast response cars, an ambulance, a paramedic duty manager were also at the scene to help.
The hailstorm that was falling at the time of the collision affected a huge swathe of west and central Herts and south Beds.
Fire crew Red Watch Watford posted a photo of collision on the social networking website.