For much of the past decade, a sallow rainbow has hung over the United States of America. Variously burning yellow and orange (and, once, a vivid red), its flickering light painted the country in fiery hues and cast menacing shadows across the home of the brave. At every airport, on every rolling news station, the colour-coded terror alert level glowed like embers from the ruins of the World Trade Center, a constant reminder of the threat of violence that citizens faced.

But now, it seems, the skies are clearing. Following an internal review at the Department of Homeland Security, recommendations have been made to scrap its Threat Advisory System. The pentachromatic system is one of the most potent symbols of the Bush administration and of post-9/11 America, which might be reason enough for the new regime to dismantle it. But in the end the terror alert level was rightly judged to be broken beyond repair.

Launched by Secretary of Homeland Security Tom Ridge in 2002, it met with immediate scepticism, quickly becoming the butt of jokes by political cartoonists and Saturday night TV comedians. Condensing a myriad of intelligence on potential threats and applying it equally to 300 million citizens as a colour was too simplistic. At a time when people desperately needed to understand the new age of warfare that the US had entered, a set of cards in primary colours smacked of condescension.

But before we get too smug, it's worth noting that the UK's own terror alert system, BIKINI, had been in place for over 30 years at this time. This one only had four colours: red, amber, black and the lowest level, white – a placid state that it never reached. In fact, the poor calibration of these terror barometers is a common theme. Since its inception, the US system has never fallen below a yellow "elevated" state to blue or green (a characteristic shared by the UK's current multi-coloured system which succeeded BIKINI in 2006). No US politician was willing to risk suggesting the alert be taken down a notch for fear of being seen as "soft on terror". For the past five years it has remained stuck on yellow, venturing no higher despite a string of credible terror alerts within the US.

But the terror alert level's apparent inability to reflect real terror events was only part of the problem. Pat Boyle is the manager of the national severe weather warning service at the Met Office. In favour of colour-coded warnings, she says: "The traffic light system is something that has no language barriers, and it has real resonance with people." But she cautions that warning systems need to be practical. "I think a good warning service has to give people simple and clear instructions that we can actually carry out. It's about 'when you see this, these are the actions that you could or should be taking'," she says. "If you don't know what to do with a warning then the warning isn't much use."

Unfortunately citizens on both sides of the Atlantic have been left mystified by what, if anything, they were supposed to do in response to non-specific terror threats. The Home Office terror alert webpage even goes so far as to advise readers that "you should not let the fear of terrorism stop you from going about your day-to-day life as normal."

So what, then, is the point?

It's hard to judge the psychological impact that 2001's terror attacks had on America unless you were there to see it. The country that was in possession of both the largest standing army in the world and the majority of its nuclear weapons could not comprehend how a few men with craft knives could have wounded them so severely. I remember a picture pinned to the wall of my local Greyhound bus station: America's fleet of stealth fighters lined up for a photo op, with text added "CAN OSAMA COME OUT TO PLAY?". It perfectly summed up how incapable many were of understanding how to face the threat of terrorism. In that climate, the terror alert level at least gave citizens some sense of control – a belief that the authorities had their eye on these invisible agents of a stateless army and were ready to pounce.

But like BIKINI, the Homeland Security Advisory System was never designed to be a public information tool. Far from being impotent, changes in the alert level had a direct effect on the security detail of hundreds of sites: keeping the country on orange alert cost $1bn a week in additional security. The system worked well at a federal level, where management of these resources was centralised. Whatever replaces the terror alert system will try to keep these effective parts while also serving the public better.

Strange as it seems, I'm going to miss that little rainbow chart. The embossed edges, the sharp imposing Bank Gothic font, the stark warnings barked with utterly no context. Over the past decade it's become part of a collective consciousness, a nation's anxiety summed up in a single graphic. And for that reason, I'm also happy to see it go. The skies are clearing over America, and it's time to stop being scared of terror.