Corrected entry: At the first overpass Alice tries to use the motorcycle that's just sitting there, strangely clean. She doesn't have her prints in their system so the bike won't start and she gets zapped. She gets captured by Dr Isaacs and cuts off his left hand to escape on a motorcycle carried on his armored vehicle. Later at another destroyed flyover, she gets back onto the bike and rides towards Raccoon City. No fingerprint or hand required.
Ladyrebyl
26th Oct 2017
Correction: She likely used Isaac's hand to access the bike's computer system and either re-programmed it to work with her finger-prints or simply disabled the security system so it wouldn't require a finger-print scan. She was a former head of security with Umbrella and knew how their systems worked and what they could do, after all. It'd be a lot easier to do that than carry around a hand that will likely start to rot, and nothing in the film indicates that wouldn't be possible.