The Extinction Rebellion climate change protests in London removed the cars from Waterloo Bridge and created a public space that the Garden Bridge would never have been, writes Christine Murray.

London finally got its garden bridge last week. No designer was involved and it didn't cost a penny of public money.

It happened, briefly, when Extinction Rebellion shut down traffic at four locations in London including Waterloo Bridge, in a non-violent civil action to raise awareness about climate change.

Within 24 hours the bridge, renamed Waterloo Garden Bridge, was a thriving, treelined urban space, with a bandstand, wellness tent, skatepark, market kitchen and information point. By the time it was stripped away, a petition to keep it forever had garnered 1,000 signatures.

Compare this crossing to the £200 million failed Garden Bridge project by Thomas Heatherwick, and the architects of that fiasco look like the weavers in The Emperor's New Clothes. The Garden Bridge cost £53 million without ever being built, including £21.4 million paid to contractor Bouygues, 1.3 million spent searching the Thames for unexploded bombs, £2.7 million on Heatherwick's design, £13 million on Arup's engineering and £161,000 on a website.

In contrast, it's amazing how little effort it took to make Waterloo Garden Bridge. Crowdsourced on Facebook, protesters were encouraged to bring plants, compost, straw bales and pop-up pagodas. Activists brought in large potted trees – I watched two pensioners arrive on the bridge with three-metre birches in their rucksacks.

It's amazing how little effort it took to make Waterloo Garden Bridge

Chalk was provided to decorate the road, which became a colourful canvas of messages, drawings and wayfinding. There was a tent with woodblocks to print flags and T-shirts. The lorry used to block traffic became a stage and bandstand, with activists glued to its roof and under its chassis.

There were art workshops for children to make crafts in the family tent. My five-year-old daughter planted some radishes and wildflowers in recycled tubs after practicing her skateboarding on the smooth road.

While cars were stopped by a blockade, the two pavements on either side of the wide, four-lane bridge were kept open on either side, as well as the cycle paths. Improvised street signs taped to guardrails or traffic pylons warned cyclists traffic to slow down and guided them with scribbled arrows. Returning to the bridge over several days, I saw more wheelchair-users and mobility scooters than in my twenty years in London, cruising along the bridge's open road.

I stood on the bridge as the police first began arrests on Tuesday, and the crowd was chanting: "Whose streets? Our streets." The protest held the bridge for another five days, which filled Instagram with photos of children cycling, rollerskating, late night parties and live music, including a cello soloist playing Bach, a klezmer band and a circle dance, but eventually the trees were confiscated by the police and the bridge reopened to traffic.

It was genuinely created by the people, for the people. It was cheap to deliver and cheerful, too

It was not long after that the petition began circulating, calling on Greater London Authority to "Make Waterloo Bridge a Garden Bridge". A quick trawl of #extinctionrebellion on Twitter shows just how much Londoners love Waterloo Garden Bridge. "It feels worse than ever when you've experienced vehicle-free spaces thanks to #extinctionrebellion on Waterloo Bridge" tweeted @bel4temple. "It should be like that every day, thanks #extinctionrebellion" added @FlorentinBulot.

They're right. Waterloo Garden Bridge is better than the Garden Bridge – and it beats New York's High Line, too. Why? Because it was genuinely created by the people, for the people. It was cheap to deliver and cheerful, too. Not an inch of it was over-designed or over-engineered, which made it feel less precious and more fun. You were allowed to draw on it. It didn't get pretentious with wildflowers and weeds. And because it felt unfinished, it offered an invitation to come and complete it.

You were also allowed to cycle over it, which neither the High Line, nor the Garden Bridge would allow – and it actually leads somewhere useful, so it isn't just a touristy detour. Plus, it was smooth and properly accessible, with no stairs and a gentle onramp. Why do we make pavements so bumpy and awkward, with fussy joints of stone or interlocking brick? What's with meandering paths through parks when straight lines are ace for getting around the city?

Thousands of Londoners, whether engaged in the protests or not, have fallen in love with car-free streets

The protests have continued, although the last of the road closures – at Marble Arch – is expected to be vacated later today. As the roads reopen to traffic, two things should give designers pause: One is the fact that thousands of Londoners, whether engaged in the protests or not, have fallen in love with car-free streets.

"I would love to see Oxford Street pedestrianised and Marble Arch too. It's so wonderful there without cars," tweeted @IsabelLosada. "My toddler loved it", wrote @Boidus tweeting a video of an exuberant toddler running along the street's central white line: "Trouble is now he wants to run on all the roads." As these protests spread around the world, thousands more citizens will experience community action and car-free streets.

The second thing to note is that no complex masterplans, design interventions, landscaping, fancy benches or planters were required. Extinction Rebellion simply deleted the cars and invited the public to come and play. Next time you're tasked with designing a piece of public realm, ask yourself what can make a place beloved enough for a petition in less than a week.

As for climate change, given the broad scientific consensus that the sixth extinction has begun, we can only hope Extinction Rebellion's continued disruption will encourage political engagement and action. The lives of our grandchildren depend on it.