So I see you left the car at the gas station and grabbed that motorcycle instead. Certainly, there are advantages and disadvantages with whatever choice of vehicle you pick. Here are a few things to consider if you will be using a motorcycle to get away from those hordes of zombies.
On a car, truck, or van, you have to disengage the parking brake and put the car in gear before using the accelerator or brake. On a motorcycle you will need to know where the clutch is along with where the gears are and when to use them. To make things more complicated, you will need to know where the front and rear brakes are along with where the accelerator is located. Unless you are already familiar with riding a motorcycle, your chances of picking up a random motorcycle from the street and effectively using one will be extremely slim to none at all.
Safety and Security
If you can get past the learning curve of learning how to operate a motorcycle, these vehicles are fast! You can weave through stopped vehicles or traffic that would normally stop a car in it's tracks. Unfortunately, a bike is a open vehicle which means that you are potentially an open target while riding around. To be safe, you and your passenger would want to wear a helmets to protect yourself from head, injuries in the event of a fall. It would be ideal to wear leather or have multiple layers to protect from road rash if you crash--the best solution is to do is avoid accidents altogether as most motorcycle accidents are fatal.
A motorcycle is perfect for one or two riders. The cycle will take only a few gallons of gas but has the potential of taking you hundreds of miles. If you have got your hands on a dirt bike, you can go off road and this could prove to be very useful if you need to go off the beaten path. While riding during ideal conditions, riding in adverse weather will take its toll on you--be sure to be dressed appropriately!
If you have a motorcycle, you will do good by locating one or two gas containers to hold extra fuel. You can use a bungee cord to secure the containers to the rear of the bike. Some motorcycles have back support for a second passenger while others don't. If you don't know how to operate a motorcycle maybe you should make it a point to learn know while the time is convenient because you never know when you may need to call on these particular skills. Hey, look over there--it's a landing strip, maybe I can find a single-engine aircraft! Happy riding!