Button with code to go to hyperlink

I have some code behind a BUTTON that should obtain driving directions from two form fields:
Dim Saddress, Eaddress, CompleteURL

If values("PickupAddress") <> null and values("DropOffAddress") <> null then

Saddress= values("PickUpAddress")

Eaddress = values("DropOffAddress")

CompleteURL ="http://maps.google.com/maps?saddr=Saddress&daddr=Eaddress";
(what to put here to make user go to the hyperlink automatically in a new browser tab?)
End If
I was wondering if this would work in html, but I'd have to get the variable 'CompleteURL' first!

<asp:Hyperlink Runat="server" NavigateUrl=CompleteURL onclick="window.open (this.href, 'popupwindow', 'width=400,height=400,scrollbars,resizable'); return false;">GET DRIVING DIRECTIONS<asp:Hyperlink>