Pop quiz: What’s the speed limit in downtown Boston?

Your guess was as good as mine until Mayor Marty Walsh announced Thursday that the city’s speed limit will be decreasing 5 MPH – from 30 to 25 MPH – thanks to Governor Charlie Baker signing House Bill 4565, an act modernizing municipal finance and government.

“I am pleased that H. 4565 will give municipalities the authority to lower default speed limits,” Walsh said in a statement. “Commissioner [Gina] Fiandaca and I look forward to working with the Boston City Council once this law goes into effect to lower the default speed limit in Boston from 30 MPH to 25 MPH.”

The measure is partly to help curb traffic accidents, but it’s predominantly aimed at making Boston’s streets safer for pedestrians and cyclists – a charge Mayor Walsh has taken on full steam since a string of fatal accidents involving pedestrians or cyclists and motor vehicles within the past year.

“We know that lower speed limits are an important tool in reducing fatal and serious crashes and creating safer streets for people of all ages and abilities who are walking, driving, and bicycling,” said Walsh. “A lower speed limit in Boston would be a major early accomplishment for our Vision Zero goal: bringing the number of traffic deaths and serious injuries to zero by 2030.”