Pass Values Between Subs

Not been doing this too long, but have a question. Have a sub that determines which checkbox(s) are selected. I then want to get the value from that sub and use it in another sub that runs a query to populate listboxes.

Code so far
Public Sub TransportMode()
If Me.checkAir = True Then
strtypes = strtypes & "'Air',"
End If
If Me.checkCar = True Then
strtypes = strtypes & "'Car Hire',"
End If
If Me.checkAll = True Then
strtypes = "'Air','Car Hire',"
End If
strtype = Left(strtypes, Len(strtypes) - 1)
MsgBox strtype
End Sub

Public Sub FromToUpdate()
TransportMode

strSQL = "SELECT DISTINCT MasterTable.From FROM MasterTable WHERE MasterTable.Type IN (" & strtype & ")"
If Len(strbgs) > 0 Then
strSQL = strSQL & " AND MasterTable.BGID IN (" & strbgs & ")"
End If
MsgBox strSQL

How ever when get the message box, the value from first sub is not used by the second. How can I call it across? I'm trying to put bits of code like the first sub into many different sub as they are used again when buttons are pressed on the form etc.

cheers
Matt