I've had 2 lifetime experiences with the use of LPG as a motor fuel. When I was a teenager in the midwest my father managed a trucking operation that had summer cooling units attached to the upper front of the trailers to transport food products that required cooling. Every year when winter arrived they unmounted the cooling units and rebuilt them prior to the next cooling season. The the units where powered by 2-cylinder air cooled engines that were subjected to 24 hour start/stop duty cycles for the duration of the northern hemisphere summer cooling season. May , when the units were re-installed, through late September. When the units were off-truck, heat for cargo that had to be kept from freezing was supplied by charcoal burners carefully monitored to prevent fires.
During the active cooling season the engine oil was changed weekly. Since this was the days before synthetics it was old-school petroleum oil that went in green and came out thick and black. By the end of June some engines would start failing and were replaced with a freshly rebuilt one or a new one. That maintence cycle went on until the end of the cooling season when they were no longer needed and would be removed for the winter overhaul cycle. This went on for years until one May the units were reinstalled after having been converted to LPG and LPG refueling was installed at the company's service facilities.. Same engine brand and the fleet still had a mix of rebuilt and new engines. That year, using the same oil change cycle, the drain oil each week still had the same greenish tint as new oil and there were almost no engine failures all season. The only difference was the fuel. The engine life had been extended dramatically by just changing fuel and eventually they were able to elimiate the winter removal/repair cycle and use the units as heat pumps with no fire danger.
In later years the manufacturer of the cooling units (Thremo-King) fielded many new designs, including using a small diesel that runs continuously and engages a clutch when cooling the trailer, so the engine ran at max efficiency.
Second experience - much later in the course of my working career I lived in Europe, in one of the Benelux countries, and LPG was very popular. In the US, LPG is not distributed widely along with gas/petrol if you wanted it you had to know where the local bulk LPG distributer was. That still exists today. In Canada that's not true. In Europe at that time almost every petrol station had at least one LPG pump available right next to the petrol and diesel pumps and many autos used LPG where we lived. The main driver of fuel use was that the governments taxed petrol higher to encourage the other fuels, making those more desirable. Several of the people I worked with had LPG and, in the days before factory-installed LPG they had it installed by the dealer when buying a new car.
That was long ago when the EU was just forming and I have no idea how it is now. I don't remember seeing LPG at the pumps in Australia so how widely is it distributed?