Air doesn’t stop flowing at city borders, so we have a regional air quality board to regulate emissions and set Spare the Air days. Water doesn’t respect borders, so we have regional and state agencies setting rules for rivers, streams and the San Francisco Bay.

It’s time to start looking at traffic the same way. And that includes its root causes, including the imbalance of jobs and housing.

A border war between San Jose and Santa Clara over large developments in each city has brought a simmering problem to a boil. But it’s not just them. Intensification of development throughout the valley will affect traffic flow for everyone. Apple’s spaceship and the dead Vallco Mall ripe for redevelopment in Cupertino are right on the Sunnyvale and Santa Clara borders, for example.

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The Related Companies plan in Santa Clara that started the current battle is said to be the largest ever approved in in Silicon Valley. It calls for nearly 6 million square feet of office space and 1.1 million of retail across from Levi’s Stadium near the San Jose border. A few token units of housing, are in the plan, but they’ll never get environmental approval: The site is a closed landfill.

For San Jose’s traffic concerns, it’s the lack of accompanying housing that raises alarms. Santa Clara already has two jobs for every housing unit needed for its workforce, not counting the more than 25,000 new jobs likely in the Related plan. The city will be more than 20,000 homes short of what’s needed for those jobs. Roads will be overwhelmed. San Jose’s concerns are legitimate.

California environmental law requires cities to study impacts of proposed development across borders, but it does not require mitigation in other cities. Sometimes cities and developers agree on plans. Sometimes it takes a lawsuit.

That’s what happened more than a decade ago when San Jose proposed a new plan for more intense development in North San Jose, and Santa Clara sued. A negotiated settlement followed. This time, it’s San Jose suing over Santa Clara’s Related plan.

Earlier this fall, Santa Clara Mayor Lisa Gillmor said her strategy to fight off San Jose’s lawsuit would be to attack San Jose projects near the Santa Clara border. Soon after, Santa Clara filed a challenge to Santana West on Winchester Boulevard near Santa Clara’s city line. We’re not seeing the issues with this much smaller development plan — less than a million square feet. But this is what happens when lawsuits are the weapons of choice.

San Jose has more housing than jobs for residents, the opposite of Santa Clara. It’s the reason Santa Clara is a much richer city per capita. Revenue sharing from jobs in one city to subsidize housing in another could be a remedy in cases like this. But that discussion will take regional leadership. We’d like to see someone accept that challenge.

In the meantime, Santa Clara and San Jose need to settle the dispute over Related, stop the tit for tat lawsuits and move on.