Perhaps we all have one distinct memory of the horrors surrounding Sept. 11 that has outlasted all others, that singular instance when we felt the full magnitude of the tragedy and sensed that it had changed us and our world in ways we had yet to understand.

Mine unfolded over more than eight hours and 500 miles, on a car trip I took from Maine to New Jersey a couple of days after the terrorist attacks. Although it’s a route I’ve taken every September for the last 16 years, the long string of interconnected highways was altered dramatically on that 3-year-old trip that now seems like a lifetime ago.

Last week, as I traveled the route alone on the way to an annual family commitment, the images of that dark time scuttled back up from memory and reappeared before me with haunting clarity.

I shouldn’t have been surprised but I was, in much the same way that a particular forested landscape can make a war veteran flash back to a battle he fought decades ago in a country half a world away.

The highway overpasses set the memories in motion. As I approached each of them, in so many towns and cities along the way, I looked up at the faded and often tattered American flags that have hung from overpasses since 9-11 and remembered the small groups of people who had once huddled there with lighted candles to mourn the loss of 3,000 innocent American lives and the unleashing of a terrible evil on the land.

And no matter what might have been playing on my car radio at the time – a baseball game or one of a dozen inescapable shrieking talk show hosts who fill the airwaves – I could hear instead the patriotic music that played all that day three years ago and the voices of people who felt compelled to call the stations and pour out their grief, anger and sorrow at what had happened.

Crossing the Hudson River, I glanced toward Manhattan in the distance and, through that powerful trick of memory, saw the island once again under a pall of dark smoke and the mountain of rubble on which my firefighter cousins clawed for days to find their friends who had been buried there.

But even the strongest illusions soon pass, and the new signs that have appeared on the overpasses in the last couple of years – the ones that welcome the local heroes back home from Iraq – are stark reminders that time did not stand still for an instant after 9-11.

We’ve waged two separate wars since then, even if our president continues to insist that they are one and the same.

We launched an ill-conceived invasion of a country that had not threatened us and got ourselves mired in a war with no foreseeable end that has so far cost more than 1,000 American lives, many thousands of Iraqi civilian deaths, and the critical support of allies around the world who once mourned our losses on that terrible Tuesday in September.

And in the process, we Americans who once stood united in our shared grief and resolve have quickly become as bitterly divided as we were more than three decades ago over Vietnam.

I’m sure that one day I’ll be able to make that trip south without being visited along the way by the ghosts of 9-11. We all move on, after all, in our own small ways and at our own pace. At the moment, I’m more worried about this perilous new and uncharted road we’re traveling as a nation, and where it might lead us all one day.