The city is expanding its experiment with parking meters that accommodate credit cards, with another 30 of the devices due to be installed by the end of the month in Newton Centre, said Bob Rooney, Newton’s chief operating officer. A pilot program to test the alternative payment system was launched in the Newton Highlands last fall. The meters being deployed in Newton Centre are being provided by a different company, however, to allow city officials to make a comparison, Rooney said. Replacing all of the city’s parking meters would be a significant investment, and officials want to know whether it would be worth it, he said. In Newton Highlands, about 14 percent of drivers have used credit cards, instead of coins, this year. The company that provided the machines waived the usual credit card transaction fees for the pilot program, Rooney said. The city hasn’t investigated the total costs of going to electronic meters. But other factors, including the convenience to drivers and an increased ability for city officials to control the machines, are also important, he said.