Gov. Charlie Baker said last Thursday that he is “not surprised at all” that the MBTA’s monthly rider poll shows its lowest approval rating since the feature was launched more than three years ago, but he reiterated support for his transportation secretary amid ongoing frustration with the T and a controversy at the Registry of Motor Vehicles.

The T surveys a panel of riders every month on how they would rate the MBTA’s performance on a scale to 5.  In June, responses averaged just 2.5, plunging from 3.2 a month earlier to the lowest level seen.

More than half of those who answered described themselves as “somewhat,” “very” or “extremely dissatisfied,” a trend that Baker said was likely due to the “massive inconvenience” created by a June 11 Red Line derailment resulting in delays expected through Labor Day.

However, the governor touted what he described as progress toward improving the MBTA and said he still has “full confidence” in Transportation Secretary Stephanie Pollack — who is also coping with fallout from failures at the RMV to process out-of-state violation notices that, once discovered, resulted in more than 1,600 drivers having licenses suspended.

“Stephanie and her team began with what I think everybody would acknowledge was a real big ball of twine at the MBTA, an enterprise that had been underinvested in for 25 to 50 years depending on who you talk to,” Baker said. “The first serious investment in the core system, which is about improving reliability and dependability and modernizing the system, started when we took office.”

His comments to reporters came after a ribbon-cutting event marking the opening of an affordable housing facility in Brighton, where Boston Mayor Marty Walsh earlier said that he will meet with MBTA General Manager Steve Poftak next week to discuss ways to improve transit service.

Walsh told reporters at Thursday’s event that business leaders have expressed concerns over the quality of public transit, including one who has stopped taking the train in the wake of the derailment.

“We can’t have that,” Walsh said. “Once you lose a rider on the T, it’s going to take years to get them back, so we can’t start losing riders on the T. It’s only going to cause another problem, a bigger problem than we already have with cars and congestion.”

In his letter, the mayor asked state transportation officials to invest about $9 million in added Red Line service to mitigate the ongoing delays. Walsh said he does not yet know if that request will be successful, but hopes to bring it up when he sits down with T brass next week.