The winter storm that wreaked havoc across metro Atlanta on Tuesday highlighted both the best and worst our city has to offer. Throughout the region, stories of good Samaritans coming to the aid of stranded fellow citizens were an inspiration to us all. That goodwill, however, played out against the backdrop of a regional transportation system that had broken down on an unprecedented scale.

Going forward, there will be no shortage of discussion about what contributed to that failure, from our thin fleet of snowplows to local school closing policy. And while there were many factors at play, there is one issue whose importance cannot be overstated: our lack of a truly robust regional transit infrastructure.

Had such a system been in place Tuesday, the outcome could have looked very different. Mass transit, and particularly rail transit, offers a level of everyday resilience and reliability that simply isn’t afforded by the roadway network. With severe weather events becoming more frequent, building a region that is more resilient to sudden disruptions is of utmost importance. And a more balanced transportation system — meaning less reliance on driving and strengthened regional transit — will be critical to achieving that.

To be fair, we have the start of a solid regional rail network in the existing MARTA system, and it indeed played a vital role this week. At times, it was safe to say that trains were the only part of the regional transportation network functioning at all. MARTA deserves credit for its extraordinary efforts to keep the system running under very difficult circumstances.

For those who take the train to work, Tuesday’s commute was largely a routine affair. My trip home from Decatur to Midtown on the Blue and Gold Lines was unremarkable, despite some lingering disruption from an earlier fire that was quickly contained. There are also stories of MARTA serving as a last resort for stranded motorists. One of our members hosted a friend overnight who, eight hours into a suddenly epic commute from Alpharetta to Smyrna, ditched the car near a rail station and rode into the city instead, where shelter awaited.

As indispensable as MARTA was this week — and is every day to those of us who rely on it — the sad reality is that mass transit in its current state simply isn’t a realistic option for many area residents. And given how we have underinvested in transit amidst the region’s explosive growth, nothing short of a major regional expansion will allow us to catch up.

The challenge of building such a system can admittedly be daunting at first, if for no other reason than cost, which will be billions of dollars. But if we learned anything this week, it should be that the cost of maintaining a heavily car-dependent status quo is even greater. We can’t afford a repeat of what happened Tuesday. In short, we can’t afford not to build the transit system our region deserves.

David Emory is president of Citizens for Progressive Transit