In the early days, it took artists weeks to paint directly onto the trams. The Preston Tramways Workshop was the studio and the state government funded paints and brushes. Mirka Mora's was first out of the depot and featured her familiar folky, loopy art motifs. On the strength of its popularity, organisers commissioned more artists.

Looking at the photos of the old trams there seems to be a particular freshness and spontaneity to the designs; those old designs seemed to belong on a tram. Or was it just the context of the old art trams that made them a novelty? Melbourne looked pretty drab in the '70s and '80s, but then imagine a supersized Howard Arkley painting on a W Class ripping through. It was sensational. Craig Gough painted his 1979 tram an intense red because, he said, he wanted it to be like "a riotous jazz band" as it cut through a Melbourne winter.

I spoke to cartoonist Michael Leunig about "his" 1986 art tram and what he thought of today's trams. "I'm probably getting old, but it's hard to tell what is an art tram. There's so much advertising around. The world is saturated with photos and imagery. We have a kind of graphic fatigue."

I half-agree with him, although I reckon art tram designs today are liberated from what can be achieved with a bucket of paint and brushes. The romance of an artist making work hasn't gone away. In fact there's the new possibility to adapt any media, such as a pencil sketch, photo-collage, digital drawing or the image of a 3D work, to the surface of tram.

It's undeniable though that the production of an art tram has lost its romance. Artists' work today must be scanned, photographed or digitally manipulated on a computer so it fits the shape of a tram (with consideration of doors, signs and lights). It is then emailed to people who print it onto vinyl decals. It takes about 10 days to prepare the vinyl after which a team of eight spend almost seven hours applying it to the tram. It's a tricky process, apparently, especially lining up the solid body vinyl panels with the clear-focus perforated vinyl that goes on the windows. Artist have nothing to do with any of this, which makes their trip to the Malvern Depot to see the finished tram a nerve-wracking experience.

Standing in front of my 23-metre-long illustration on a C-Class tram in the depot last month I felt more than a little nauseous. (It took a while to go from feeling like a show-off to feeling happy with myself, but I got there.) The approach I had taken was to simply create a pretty-looking image of people swimming, done in pencil and watercolour on A3-sized paper. It was my fifth attempt at applying for an art tram so I was beyond caring if I got in or not, beyond over-thinking it, and perhaps this freed me up. I had scanned my image at a ridiculously high resolution so the detail and imperfections in the watercolour paper and pencil lines would be accentuated. Looking at the tram in the depot I saw this technique had paid off, with the surface looking less like vinyl and more real paper, more tactile, like the old painted art trams.

Whether deliberate or not, other designs this year also seem to hark back to the old art trams. In a similar vein to Gough's "noisy" jazz band, Innocent's design is designed to make actual music; viewers are invited to download a phone app and point the camera at Innocent's tram as is passes, which in turn converts the tram's imagery into a tune.

"I'm interested in 'playable cities'," Innocent says. "The motion of a tram is like the movement of music." Innocent's art practice is concerned with how streets are "activated" by art and new technologies. He was assigned the C2 tram, the city's longest at almost 33 metres, to allow for a long musical track.

"My artwork has a collection of codes, layers and structures that activate a musical system programmed into the app."

In a way Innocent's tram is played like a pianola, but the melody can change depending on the speed of the tram and how far away you are. Visually, the tram itself is a splendid collection of abstracted geometric shapes and symbols that Innocent says may accidentally reference old-school graffiti you might have seen along train tracks in the 1980s.

"I created a half-size prototype of one section of the tram to test the technology, but I didn't know if it would work right up until I saw it at the depot. Thankfully it did."

I asked Leunig if he had had any worries about how his tram would look. "I just painted it directly on; just related to tram as I went." It took him a few weeks. "It was a big, physical job, painting that tram. A dirty process. Lots of toxic paints. Was hard to breathe."

He recalls painting in the Preston depot on a bitterly cold night 32 years ago.

"I worked at night to get away from the tradies who would gather around me and crack jokes during the day." He thought about the "great cargo of people it had carried", saying he wondered if his tram was the same tram he sold newspapers on as a kid, the Footscray to Moonee Ponds tram.

He doesn't care where it is now and regards it as an ephemeral project. "I've heard conflicting rumours it's either in Washington State in the US or rotting in a paddock near Bendigo."

Actually, Leunig's tram is one of 15 out at the Newport Railway Workshops still in good condition and stored undercover. Many decommissioned trams have ended up at Newport or at one of 17 tourist heritage groups around the state who are looking after old public transport. Larwill's 1986 tram is out there too. Ingeniously, it was photographed and reapplied to a tram this year for the Festival. It signals a new aspect of the Melbourne Art Trams project that taps into the public's fondness for the old trams. Mora's tram is now privately owned but Holloway told me he'd love to see a re-creation of that first art tram in next year's project.

Artist Stephen Baker spent a lot of time working on his art tram design. Like me, this was Baker's fifth attempt, so he gave himself more time to develop an idea. "You don't want to do something you don't like because you might get asked to do it again and again. In the end I just decided to go with something that made me happy."

Baker's tram depicts blue and red figures working together to assemble something. It is a style of work, he says, reserved for his non-gallery work. "I wanted to tell a story that touches on community, a story that reflects on the idea of Melbourne being put together."

The sight of his tram trundling past a cafe was thrilling; he's used to seeing his murals in public places across Melbourne but this "was more mechanical, solid. It reminded me of painting on toy cars and trucks as a kid."

Hayley Millar-Baker was petrified at seeing her completed tram. "Any mistakes I might have made would be pretty obvious at that scale."

Her work is inspired by her Aboriginality and her family's struggles and triumphs. However she began designing her tram thinking about creating a feeling. "I wanted to recreate that feeling of being out in nature, that calm, comfortableness you get when you step barefoot onto an isolated beach."

Millar-Baker's work draws on her connection to local Indigenous communities and depicts the land of south-east Australia before, during, and after colonisation. A collage of black-and-white photos tells an earnest story of her mother travelling over rocks with a crew of native Australian animals. The animals are Aboriginal totems and the boulders that make up the bottom half of the tram are of Lake Condah in western Victoria, a bit north of Portland. "It's where my family lived for 60,000 years."

The black-and-white work provides some respite from the cacophony of the city generally. "Elders have said they are proud of it, and love that there's an Aboriginal story moving about the city like this," she says.

It's a nice idea, that of a culture, a feeling or an expression moving through the city by way of a tram. The modern art trams may not command the attention they once did, complete with both the visual junk of modern life and other trams decked out in advertising, but I imagine the average punter walking down Swanston Street knows the difference. Especially when, as Holloway describes it, "you realise that they are not trying to sell you anything or persuade you to believe in something".

You can vote for your favourite art tram at festival.melbourne/2018/events/melbourne-art-trams/peoples-choice-award/