One warm spring evening, two Philadelphia families experienced tragic and eerily similar losses. On April 13, in two different parts of the city, Josephine Rivera and Dominique Lockwood lost their sons to hit-and-run drivers.

Josephine, of Kensington, lost her 2-year-old son, David Alicea, and Dominique's son Abdul Latif Wilson, 4, was killed.

Many others have lost their lives, including filmmaker Jay Mohan, 26 of Brewerytown, on May 11; Theresa M. Pozzi, 33 of Holmesburg, on Dec. 23; Vincent Peary, 69, of the Northeast, on June 20, 2014; and Zachary Woods, 27, a Wharton student, on May 6, 2014. Among those critically injured are Rachel Hall, a 22-year-old Temple student, who was hit on April 29, and Michael Toner, 68, a Philadelphia actor whose leg had to be amputated after a crash on June 9.

Each year, Philadelphia and its neighboring counties experience traffic violence that kills or critically injures nearly 100 people. To read the accounts of these horrific crashes is to read of bottomless grief — so many questions with rarely any answers.

But we do know one thing. These deaths and injuries are preventable. We have the knowledge and tools to prevent these tragedies. It's called Vision Zero.

Vision Zero originated in 1997 in Sweden, where city planners and traffic engineers began addressing the frequency and severity of car crashes by redesigning streets to encourage safe and responsible behavior. The movement, which has since spread throughout the world, addresses two primary causes that lead to severe crashes: poorly enforced traffic laws and poorly designed streets and intersections.

Cities that have implemented Vision Zero strategies have not only seen reductions in deaths and injuries, but have begun changing the discourse on traffic violence. New York City, which treats the issue as a public-health crisis, has stepped up enforcement and seeks punishment for negligent drivers. This has meant increased accountability for drivers, including police vehicles, public transportation, and large delivery trucks. The changes have created conflicts among, city government, the police, and even public transit unions, but Mayor Bill DeBlasio has not backed down. As a result, traffic deaths and injuries are on the decline.

It has also committed resources to identify and reengineer the most deadly parts of the city's transportation network. Queens Boulevard, nicknamed the "Boulevard of Death," is being redesigned to help prevent speeding and provide greater refuge to vulnerable pedestrians and cyclists. Philadelphia could use a similar vision on North Broad Street, Roosevelt Boulevard, and Walnut Street in West Philly. Many have lost their lives or sustained serious injury on these wide, fast, unsafe urban arterials. We must transform our streets from places of fear to vibrant public spaces that safely accommodate multiple users, not just motorized vehicles. Public safety is one of the most vital roles of government, and it is critical to recognize the impact that poorly planned infrastructure has in undermining this role.

Traffic enforcement will be key. Speeding multi-ton vehicles kill. Even a slight speed increase in a crash involving a pedestrian or cyclist dramatically increases the risk of fatalities. So prioritizing enforcement on speed limits, yielding to pedestrians in crosswalks, and driving without distraction are all crucial.

Success with Vision Zero in Philadelphia will require focus from our mayor and City Council. Jim Kenney, the Democratic nominee and favorite to win the mayoral race, has proven he understands the issues. For example, he has fought to ensure that contractors provide barriers to protect pedestrians in temporary walkways when sidewalks are closed during building construction. The appointments he makes in agencies responsible for public infrastructure will be critical to maintaining the momentum to reduce and eliminate traffic violence.

Proper funding for the Streets Department is crucial to increasing traffic safety. Currently the agency is repaving streets on a 15-year schedule, but this timetable delays implementation of safer-street infrastructure that the Planning Commission has previously planned for and future interventions Vision Zero legislation can help shape.

It will take sustained effort to not only change the physical form of Philadelphia, but to change our culture of policing and enforcement. This kind of reform will ensure that nearly the 100 preventable tragedies the region experiences every year become a thing of the past.

Geoff Kees Thompson is the chair and co-founder of The 5th Square (5thsq.org), a nonpartisan political action committee committed to improving urban planning in Philadelphia. @5thsq