You can access value of any page item in any page. For e.g. P1_SHUTTLE (Page-1), P2_SHUTTLE (Page-2) are two items, then you can access value of P1_SHUTTLE in Page-2 in SQL and PL/SQL. Only restriction is you can't find the P1_SHUTTLE item on Pgae-2 HTML, so you can't get it;s value using JS.
If you want to set value of P2_SHUTTLE with P1_SHUTTLE, you can do it by creating On Load Before Header Processin Page-2 which will just do following