Availability varies. Enrollment discount applies during data collection; final discount is calculated on driving behavior and could be zero. Discounts do not apply to all coverage elements; actual savings vary by state, coverage selections, rating factors and policy changes. Final discount applies at the next policy renewal and remains until drivers or vehicles on the policy change.
You might have a roommate or family member on your policy that no longer drives your vehicles. Or maybe you have a vehicle on your policy that is no longer being driven. Making sure driver and vehicle information is up to date may save you money. Keep in mind, if you do go down to just one car on your policy, you will lose the multi-vehicle discount.
Several jurisdictions have experimented with a "pay-as-you-drive" insurance plan which utilizes either a tracking device in the vehicle or vehicle diagnostics. This would address issues of uninsured motorists by providing additional options and also charge based on the miles (kilometers) driven, which could theoretically increase the efficiency of the insurance, through streamlined collection.