Batmissile

The Batmissile is a kind of escape vehicle integrated into the Batmobile. When needed, the Batmobile can shed it's outer "skin" and form this bullet train-like vehicle that is able to pass through narrow spaces the Batmobile would not ordinarily be able to go.

Batman used the Batmissile to escape from the police after the Penguin's hijacking of the Batmobile. After failing to initiate a different function due the Red Triangle gang's tampering, Batman intiates this mode as a last resort to ditch the chasing police cruisers. The Batmissle managed to pass through an incredibly narrow alleyway, causing three cruisers to crash behind it and allowed for a speedy retreat back to the cave.

Background Information and Notes
A similar concept would later be used in 2008's The Dark Knight. After the Tumbler is catastrophically damaged, it folds and jettisons the parts around it's two front wheels into an escape vehicle called the Batpod.