For the second time in about six months, a traffic-stopping hole has appeared in a major city street as the result of collapsing sewer lines.

Where will it happen next?

Apparently it is hard to tell, given the condition of portions of the city’s aging infrastructure.

In February, the intersection of Eighth and Kentucky streets was closed for about two weeks while city crews excavated and repaired a collapsed sewer line that had caused the street above it to give way. This week, a similar situation occurred near the intersection of 14th and Tennessee streets, but repairs are not expected to take as long because the line was smaller and not buried as deep as the one at Eighth and Kentucky.

Age is being blamed for the line failures. City officials said Monday that they didn’t know exactly how old the line was, but it was old and scheduled for replacement next summer.

That will solve the problem for one section of street, but how many other aging sewer lines are lurking beneath Lawrence streets? Will street collapses become a common occurrence during the years it takes to catch up on sewer line replacements?

The larger question here is how the city allowed itself to get in this position. City commissioners are looking at a 50 percent increase in the city’s street maintenance budget in an effort just to keep the backlog of work from getting worse. It will take even more money to step up the schedule for replacing streets that are beyond repair.

Water lines, sewer lines and street pavement don’t last forever. When the city installs such infrastructure, it seems officials should have a pretty good idea what it will take to maintain them and what their useful life should be. The sewer line that collapsed at Eighth and Kentucky was more than 70 years old; the water lines that are being replaced along Massachusetts Street this summer are more than 100 years old. Is it any wonder they were starting to deteriorate?

Just waiting for aging infrastructure to fail, then replacing it, doesn’t seem like a winning strategy. City crews will spend days patching the latest hole on Tennessee Street, which apparently is scheduled to be torn up again to replace the entire sewer line next summer. The replacement work can’t be done now because the engineering for the project isn’t complete, but this is an expensive way to do maintenance. How much could the city have saved by replacing the aging sewer lines before they collapsed and created the need for expensive street repairs?

To their credit, current city commissioners are asking many of these same questions. After many years of just getting by, the city needs a long-term strategy that includes a regular, ongoing maintenance program allowing it to avoid the costly crises it now faces regularly.