SAN FRANCISCO – California air-quality regulators are considering a requirement that big-rig trucks install computer systems to pinpoint on-the-road emissions problems, a move that could spur a change in federal rules. The California Air Resources Board, or ARB, is expected to vote on July 21 on what would be the first such regulations in the United States for heavy-duty trucks, and the federal Environmental Protection Agency is likely to approve a similar rule, the ARB said. California, the most populous U.S. state, often leads the way on environmental policy, and cars and light trucks in the state already face similar...