The Registry of Motor Vehicles has begun to display a waiting times on the screens at is its branch offices, including the one in Braintree. In addition to average waiting time, the screens show staffing levels and customer volume from the most recent month, and comparisons with the same month a year earlier. “This comparative information gives customers an honest look at our operations and holds us accountable,” said Registrar of Motor Vehicles Rachel Kaprielian. In Braintree, wait times have fluctuated. In January, for example, wait times dropped to 15 minutes this year from 25 minutes in 2012. During April vacation week, the wait rose to 48 minutes from 46 minutes in 2012, mainly due to an increase in customers from the closure of several Boston branches due to the Marathon bombing. State transportation officials hope the metric will not only better inform customers, but also push them to make transactions online at www.MassRMV.com.