With the new school year already underway, I rarely go a day without riding the G train. I live in Clinton Hill. My son goes to public school in Carroll Gardens, and plays soccer in Greenpoint several times a week.

The G train could run more frequently, but we G train riders will defend it even as we grumble. After all, there is no better way to get from Kensington to Long Island City or anywhere in between.

But G loyalists endured a brutal wake-up call recently after a subway tunnel wall collapsed, causing a train to skid off the rails at the Hoyt-Schermerhorn station in downtown Brooklyn.

There were only a few injuries, but who knows what might happen next time? The accident, apparently caused by a water leak, is a harsh reminder that fixing city infrastructure could be a matter of life and death.

In an ad in several newspapers (including amNewYork), and in fliers distributed citywide, Transport Workers Union 100, which represents MTA employees, argued that NYC needs to contribute more to the authority's capital budget for repairs that would prevent horrible accidents.

The union's right. An Independent Budget Office report in June found that the city was underfunding the MTA, and that the authority was behind on many capital projects. But where could the money come from? Part of the problem is setting priorities. The budget office found that the city's contribution to the MTA had declined as a percentage of the overall budget.

The city should fight as well to raise taxes on top earners and corporations, especially considering how much big business benefits from NYC public transit.

That is tough in Gov. Andrew Cuomo's Albany, but the Citizens Budget Commission has some other ideas, including a vehicle-miles-traveled tax on motorists. This would create an incentive for New Yorkers to drive less and use mass transit -- improving air quality and increasing funding for the MTA. The commission, a nonprofit group focused on city and state finances, also has recommended reforming and expanding sales taxes on the taxi industry as an additional source of MTA revenue.

The commission recommendations should be seriously considered. Our lives are at stake.

Liza Featherstone lives and writes in Clinton Hill.