Mitsubishi PHEV is a silent worker

...to precede a horseless carriage to warn the unsuspecting populace of the danger approaching at 3km/h.

Fast forward to the digital age. The advent of the electric vehicle has brought a similar development — the EV now has to make a car-like noise to alert pedestrians of its near-silent approach.

So it is with Mitsubishi's clever-bordering-on-complex Outlander PHEV, on sale next week. Below 3km/h, the "world's first plug-in hybrid SUV" — its main claim to fame — rolls along silently.

As it accelerates up to 35km/h, the Acoustic Vehicle Alerting System emits a rising tone that sounds like, well, a car in motion. Beyond that, tyre noise and air displacement evidently give enough aural clues that it's coming.

At highway pace, the Outlander's 2.0-litre petrol engine cuts in, audibly, with some of its 87kW. Decelerating from 32km/h, the PHEV again emits the acoustic alert, from a speaker tucked under the nearside front mudguard.

The British red-flag laws were repealed in 1896. In these litigious times, there is probably still scope for an earphone-wearing boofhead to take action against the driver of a car that emits a warning noise he can't hear.

A  veritable United Nations of engineers is at work on industry standards for EV acoustic warnings. Mitsubishi EV product manager Ashley Sanders says the US federal safety body and Japan's road transport ministry are collaborating with the car makers.

"US legislation came in 2010, Japan in 2009," Sanders says. "EVs have been in mass production only since 2008 so frequently it's technology that's driving the regulations. Not all the competitors will develop their technology the same way. There's no specific decibel level or tone, the tech has to meet noise profiles on a range of speeds."

They won't be mistaken for phone ring tones. On the prohibited list are the sounds of sirens, chimes, bells, animals, insects and waves. Meanwhile, it will be a long time between drinks for the Mitsubishi line-up. Literally for the Outlander PHEV, which claims 1.9L/100km, but also unfortunately for fresh product.

There will be a new Triton ute later this year, a Pajero next year ... and don't hold your breath for the Lancer to replace the CJ series that's been around since 2007. On the brighter side, Mitsubishi Motors reckons plug-in hybrids and electric vehicles will account for about 20 per cent of its production by 2020.

The next-generation Pajero will borrow heavily from the GC-PHEV seen at the Tokyo show with 3.0-litre supercharged V6, 70kW electric motor and eight-speed auto. It promises 40km EV range and hybrid thirst of 6.6L/100km. The next ASX, ostensibly model year 2015, was previewed in the compact XR-PHEV concept, with 85km electric-only range and claimed 3.5L/100km.