Yes, Boston, there’s a speed limit. Post it.

Mary Pasciucco, who has lived on Beacon Street for 20 years, talked about an accident in March where it is believed that cars were drag racing. Pat Greenhouse/Globe Staff/Globe Staff

As Boston takes greater notice of the role pedestrians and cyclists play in the local transportation system, there’s a flurry of interest in new ways to prevent people from being hurt or killed in automobile crashes within the city’s borders. A municipal website maps accidents that cause injuries and fatalities. Activist groups ponder subtle streetscape design changes that would nudge drivers to be more cautious and alert. Recently, City Councilor Frank Baker filed a home rule petition that would allow Boston to set speed limits lower than those provided in state law.

Here’s one more idea: Whatever the speed limit is, post more signs notifying motorists of it.

Under state law, the default speed limit for motor vehicles in thickly settled areas is 30. (Baker’s proposal would allow the city to reduce that limit to 20.) Some drivers with local roots may remember the current rule from driver-education classes. But others won’t, and most migrants from elsewhere have never been taught the rule to begin with.

Other jurisdictions where speed limits follow general rules do not presume that everyone knows what those rules are. For instance, in New Orleans, where major streets generally have wide median strips, signs all over the city remind motorists that speeds are limited to 35 miles per hour on divided streets and 25 miles per hour on undivided ones. If Boston wants drivers to slow down, making the rules more explicit should help.

The idea that traffic moves too quickly in Boston may come as a surprise to motorists who ply the city streets only at rush hour. If the city’s sclerotic traffic has an upside, it’s that when vehicles are merely creeping along, the crashes that occur are far less likely to cause physical harm to anyone — motorist, cyclist, or pedestrian.

Yet recent car-pedestrian accidents on Beacon Street in the Back Bay or Humboldt Avenue in Roxbury offer grim reminders that even a congested city has stretches of unobstructed road that turn into speedways at certain times. The default speed limit of 30 miles per hour may be too high for some city streets. If nothing else, the city needs the ability to bring down speed limits on certain classes of streets without doing a separate traffic study on each and every one.

And whatever the speed limit, people need to know what it is. While ignorance of the law may be no excuse for violating it, greater awareness of its specifics could save lives.