Just before noon on Thursday, a red Honda Accord heading south through Times Square made a U-turn against traffic at 42nd Street. It mounted the west-side curb and plowed through pedestrians for more than three blocks, killing an 18-year-old woman and leaving blood on the streets.

It prompted immediate concerns of terrorism. Cable networks went live to the scene and Twitter hit five sirens. Some Tweeters, like GOP candidate for city comptroller Michel Faulkner, went beyond thoughts and prayers for victims and called it a “possible terror attack.”

When he got to the scene, Mayor Bill de Blasio said there was “no indication” that the crash had been an act of terror. By then, a perpetrator was in custody — Richard Rojas, a 26-year-old Bronx resident who de Blasio said was a U.S. citizen and veteran of the U.S. Navy. Rojas had previous DWI arrests and had been arrested last week for menacing. On Thursday, he attempted to flee the scene before being tackled by good Samaritans and a traffic enforcement agent. He also told officers that he was hearing voices. With Rojas in custody and the danger over, the conversation turned to what, in fact, happened.

A ‘very serious incident’

Within hours, what de Blasio had called a “very serious incident,” was in the process of becoming more a matter of street design than national security. Council member Ydanis Rodriguez, transportation committee chairman, observed the scene and noted on Twitter that the car appeared to have been stopped by metal “bollards,” the sturdy barriers placed in front of places like federal offices and downtown banks. The car was leaned up against them.

“We need more placed around our most vulnerable places,” he tweeted. A spokesman says Rodriguez filed legislation to add more bollards to locations about two months ago and is now speeding the process up to safeguard heavily trafficked areas.

Other transportation advocates went further, saying the problem was that there are too many cars on the streets in the first place.

New York City has seen fundamental changes since 9/11 — a more obvious heavily armed police presence, for example, hired and trained in the name of safety. At the same time, the city also has changed in search of safer streets, including by building new pedestrian spaces such as the one carved out of much of Times Square under the Bloomberg administration.

Transportation safety advocates urge the city to go further to prevent fatalities.

How can the city make us safer?

Just as in facing the threat of terrorism, city government has attempted to safeguard people in and around city streets through de Blasio’s Vision Zero program, which has included more pedestrian islands and protected bike lanes, among other changes.

Those have had some positive effects, and this week the mayor announced a 12 percent decline in traffic fatalities so far this year vs. the same period last year. But that still amounted to 69 deaths, a number indicating the persistent low-level odds of danger for simply being in or near a street.

Seventh Avenue’s sidewalk was particularly dangerous for a moment on Thursday, a kind of danger from an erratic actor that city policies may inevitably struggle to block.

Ikbal Hussein, 24, was selling bus tickets to tourists on 45th Street when he saw the car launch onto the curb. He and others began running toward 46th Street and away. When he heard the crash and saw fire exploding from the vehicle, he started filming. His video shows others running, and though Hussein’s camera hand was steady in the moment he was full of nerves later in the afternoon, blocks away from the incident.

“It’s not good,” he said.