Don’t mix traffic jams with espresso. That’s my earnest advice. I did it once. I was pregnant at the time, in my defence, and hadn’t had caffeine in months. When we hit the traffic jam shortly after I’d had my unaccustomed hit of rage juice, I transformed before my own eyes into a demon, uttering unrepeatable profanities, at volume, with sign language for the hard of hearing (we were already late, of course; we’re always late). I felt like I was having an out-of-body experience. I can still see the alarmed eyes of the driver ahead, framed in his rear view mirror. Part of me felt exactly the way he did: what on earth is wrong with that woman? The New Age guru Deepak Chopra once said: “If you’re stuck in a traffic jam, you can get angry and honk your horn, or listen to Mozart.” It’s just as well for Deepak that he was nowhere near me that day.

Traffic jams are frustrating; traffic jams are stressful. Everyone who has ever sat behind a steering wheel knows it.

But they’re not just annoying; they are also bad for the economy. Places where there are repeated bottlenecks add cost for businesses in wasted fuel and delayed deliveries. They make people late for work and hospital appointments and onward connections. Snaking queues stuck behind slow-moving vehicles can also push drivers to attempt dangerous manoeuvres. Sometimes those end in tragedy.

These things explain why calls to halt the building of new roads can feel pious, jarring, divorced from reality, even. After all, ours is a road-based economy and society. We can’t change that overnight. If we want people in rural Scotland and the north to be “connected” like the central belt, then surely it follows we need to back it up with road improvements?

That used to be the last word on the subject, and for some it still is.

But something has shifted. For many people, there’s a nagging unease about the old orthodoxy. The last 12 months have brought a mass awakening, not just in the UK but across the world, to the urgency of the race to tackle climate change. The Green Party and environmental charities could once be sidelined as just another interest group making unreasonable demands. Ministers nodded and smiled as they eased them out the door.

But what used to seem outlandish now feels not just reasonable, but urgently necessary.

The basic problem is this: emissions from transport are rising (they’ve gone up for four years in a row), putting Scotland’s entire climate mitigation effort at risk. You build more big roads and what will happen? You’ll get more cars.

This is down to the phenomenon of “induced traffic”. Build more roads, get more cars and, in time, more of the gridlock and delay you built the bigger road to prevent.

Last week, there were signs that the new Forth road bridge is falling foul of induced traffic, or the inexorable increase in car use, or both. Ministers had promised that any increased traffic following the opening of the Queensferry Crossing would come from public transport. What has actually happened? 28 million vehicles used the bridge in the 12 months to October, compared to 26.7m the year before and 26m the year before that. And now there is lots of annoying congestion.

Imagine for a moment if 30 or 40 of those cars at a time could be taken off the road and replaced by a reliable bus. Even motoring organisations are slapping their foreheads in disbelief that better public transport has not been put in place to help reduce car use. Oh, the irony.

Then there are the gargantuan sums set aside for road-building schemes. The Scottish Government has allocated £1.55 billion to rail and bus travel this year. But billions and billions are being spent over the coming years on huge road schemes. There was conspicuously no transformative change in priorities in yesterday’s budget speech. “In no way a climate emergency response, but a modestly-tweaked business-as-usual response,” sniffed sustainable transport group Transform Scotland.

The answer is electric cars, some say, and they are right, in part. But in Scotland, where the target for phasing out new petrol and diesel vehicles is 2032, there will be gas-guzzlers on the roads for years afterwards. If between now and then, traffic flows have increased, encouraged by Scotland’s enticing network of gleaming new roads, then where will that leave the SNP’s much vaunted zero by ’45 target?

For a long time, the Scottish Government has managed to face both ways on this thorny question, but now things are coming to a head over the its two massive road-building schemes, the dualling of the A9 and the A96, serving Inverness and the Highlands and costing £6bn. But Patrick Harvie, the Scottish Greens’ co-leader, has indicated that support for the SNP budget this year could be contingent on scrapping the projects.

Fat chance. Politicians are in the ingratiation business and if that’s the price of Green budget support, then the SNP are likely to find an easier compromise working with the Tories. Nicola Sturgeon has problems enough without making herself persona non grata in the Highlands.

But these must surely be the very last major roads-building projects sanctioned by this Government. It’s always easier to give in to voter demand. If people ask for more roads, then give them more roads. “Leading from the front” – political code for upsetting voters – is always a scary prospect. But it is hard to see how Scotland can meet its climate targets without a bit of ministerial discomfort.

Scotland has an opportunity to dazzle the world in November, at the UN Climate Conference in Glasgow, but no one is more sceptical about politicians’ targets than other politicians. What they’ll really want to know is if, have you been brave enough to make tough decisions?

Greta Thunberg will almost certainly be there, turning her uncompromising gaze on Scottish ministers, and challenging them to Do The Right Thing, show leadership, stand up for future generations. “We avoided upsetting the Chamber of Commerce,” won’t cut much ice with Greta.

There will be no statues for building more roads.

Read more: Scottish budget: No money earmarked for second independence vote