but I couldn't figure out how the LinkedCell requirement could be defined to a relative cell
Sub AddComboboxes()
Dim cell As Range, cb As OLEObject
For Each cell In Selection
Set cb = ActiveSheet.OLEObjects.Add(ClassType:="Forms.ComboBox.1", Link:=False, _
DisplayAsIcon:=False, Left:=cell.Left, Top:=cell.Top, Width:=cell.Width, Height:=cell.Height)
With cb
.LinkedCell = cell.Offset(0, 1).Address
.Object.BoundColumn = 2
.ListFillRange = "Roads!A2:B786"
End With
Next
End Sub