Arlington County voters gave their blessing to a financial deal to build a new school Tuesday, but by then, Arlington officials had already heard from their neighbors in Fairfax County, who warned Arlington that it wanted a say in the project to avoid additional traffic in Fairfax.

The new school would be built next to Williamsburg Middle School along the county line, and Fairfax officials and residents who live near the building site said they worry that the additional traffic will make it next to impossible to drive on nearby roads.