Inside forbidden view
you can put a condition like this:
if authenticated_userid(request):
return HTTPFound(location=request.route_url('forbidden_logged_in'))
So both logged and not logged users are being redirected by Pyramid to this page, and then Pyramid redirects the logged one to another page for logged users, which by the way can be protected for example in that way:
@view_config(route_name='forbidden_logged_in', permission='user')