Hand holding

At what age would you allow your toddler / pre schooler to run ahead from you next to a main road? I am so strict on holding my daughters hand when we are near busy main roads, however others her age are allowed to run and play ahead of their parents on the grass / pavement right next to a very busy road. It really upsets my daughter as she doesn’t understand why she has to stay with me but her friends can run and play.