To reduce the insurance premium, the insured party may offer to pay a higher excess (deductible) than the compulsory excess demanded by the insurance company. The voluntary excess is the extra amount, over and above the compulsory excess, that is agreed to be paid in the event of a claim on the policy. As a bigger excess reduces the financial risk carried by the insurer, the insurer is able to offer a significantly lower premium.
But liability coverage levels come in threes — you’ll probably see something like 50/100/50 up to 250/500/250 in typical policies. You can think of these limits like: individual injuries / total injuries / property damage. Insurers are a little more technical, calling them bodily injury liability, total bodily injury liability and physical damage liability.
Those not exempted from obtaining insurance must obtain a certificate of insurance from their insurance provider, and display a portion of this (an insurance disc) on their vehicles' windscreen (if fitted). The certificate in full must be presented to a police station within ten days if requested by an officer. Proof of having insurance or an exemption must also be provided to pay for the motor tax.
In South Australia, since July 2016, CTP is no longer provided by the Motor Accident Commission.The government has now licensed four private insurers - AAMI, Allianz, QBE and SGIC, to offer CTP insurance SA. The scheme allocates one provider for 3 years as part of vehicle registration. After July 2019, vehicle owners can choose a different CTP insurer and new insurers may also enter the market. 
A lot goes into an auto insurance rate quote, including your ZIP code, coverage levels, marital status, annual mileage, driving history and vehicle make, year and model. In most states, your gender and credit history are also used to determine rates. And again, the reason auto insurance comparison shopping is so important is because rates between companies are different for each person, too.
Under the cents-per-mile system, rewards for driving less are delivered automatically, without the need for administratively cumbersome and costly GPS technology. Uniform per-mile exposure measurement for the first time provides the basis for statistically valid rate classes. Insurer premium income automatically keeps pace with increases or decreases in driving activity, cutting back on resulting insurer demand for rate increases and preventing today's windfalls to insurers, when decreased driving activity lowers costs but not premiums.
Yes, you surely can avail the NCB if you change your insurance provider at the time of renewing the policy. All you would need to do is producing a proof of the earned NCB from your current insurance provider. You can produce the original copy of your expiring policy and a certification that you haven’t filed any claim for the (expiring) insurance plan. A renewal notice or a letter stating that you’re entitled to the NCB from your previous insurance provider can be a proof for this.
You’ll notice that none of that liability coverage pays for your car or injuries, nor for any injuries your passengers sustain if you cause a wreck. This is why many people — particularly those whose car isn’t yet paid off — want “full coverage” car insurance. This isn’t actually a type of coverage, but instead typically refers to policies that include liability coverage, plus comprehensive and collision coverages.