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.
Road Traffic Act Only Insurance differs from Third Party Only Insurance (detailed below) and is not often sold, unless to underpin, for example, a corporate body wishing to self-insure above the requirements of the Act. It provides the very minimum cover to satisfy the requirements of the Act. Road Traffic Act Only Insurance has a limit of £1,000,000 for damage to third party property, while third party only insurance typically has a greater limit for third party property damage.
Over eighty years of insuring drivers has made us one of the most trusted names in the industry. We didn’t become the nation’s third largest insurer by simply offering cheap car insurance prices. We did it by offering 24/7 world-class customer support, and earning an A+ superior financial rating from A.M. Best when it comes to servicing claims. That’s why 4 out of 5 customers recommend Progressive.†† And that’s how we’ve earned the confidence of over 18 million drivers.
If the younger driver is covering his own costs, it might be cheaper for him to take out his own policy but include one of the older, lower risk drivers from the household as a named driver (as long as the older drive will use the car). However, if the older driver is footing the bill for both policies, multi-car insurance may still work out cheaper.
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. 
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.