You can find your Bike in the Map, including its durability and its current Fuel supply. You can find it manually or recover it if you’re too far away from it. You can’t fast-travel if your bike is too far away from you or if it doesn't have enough fuel. Whenever you fast-travel to a safe location, always fill up your bike’s gas tank filled. Also, items in safe Locations like fuel, materials, etc are replenished so don’t worry about running out of gas to refill your tank.
If you don’t have enough gas to fast-travel, especially for really long distances, consider traveling to nearby gas stations or cleared NERO checkpoints along the way. They will always have a gas can replenished every time to visit.
If there’s also an Infestation zone between two safe points, you can’t fast-travel between them until you clear the Infested zone. If you can’t you’ll have to manually find a detour with refueling points in between.
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