Families shop around for cheaper deals on telephone service — why shouldn't the Department of Transportation?

Streamlining several "antiquated and redundant" telephone systems under one area code and exchange will save taxpayers about $422,000, according to Secretary of Transportation Richard Davey.

The new series of numbers, which all begin with 857-DOT, is under way at several transportation sub-agencies. A major change took effect Wednesday when the main customer service line at the Registry of Motor Vehicles became 857-DOT-8000.

Drivers can use that number to get information on licenses, citations and road tests. It will even tell you the wait times at the nearest RMV. The closest RMV to West Roxbury is in Roslindale Village at 4210 Washington St., Roslindale.

State officials say they're launching an ad campaign to draw attention to the new RMV number.

Many RMV tasks can be handled at the Registry's website, mass.gov/RMV.

Since Gov. Deval Patrick shook up and consolidated the state's transportation bureaucracy in 2009, the Commonwealth has taken pains to point out savings to taxpayers. Last summer the New England Center for Investigative Reporting found that the state had oversold the financial benefits of the mergers.