Here is a reply to that in the L E T
Lancashire County Council chief answers your gritting questions (From Lancashire Telegraph)
1. The make-up of grit in grit bins is not effective, too much sand. Is that what is being used by wagons?
The gritters used to treat the highways spread 100% rock salt. The salt/sand mix used in the grit bins is proven to be effective at deicing and preventing ice from forming on pavements – the sand provides extra traction especially on snow and continues to be effective after the salt has dissolved in solution. Applied to a layer of snow, the material in grit bins will help to prevent ice from forming and provide traction. The more foot-traffic the pavement gets, the more effective the grit will be as the action of people walking is needed to activate the salt – however it is designed to prevent icing and provide traction – it is not designed to entirely remove a layer of snow.