When two cyclists were tragically killed in hit-and-run collisions this past summer, a group of anonymous urban activists known as the San Francisco Transformation Agency erected a set of protected bike lanes using traffic cones. Usually such guerrilla interventions are temporary. They raise awareness but ultimately get taken down by municipal authorities. But when the same group recently (and illegally) installed a set of soft-hit posts alongside Golden Gate Park, the city reacted by making the change official.

The SFMTrA, a play on the city’s Municipal Transportation Agency (SFMTA), “is a collective organization of men and women committed to making streets safer for cyclists and pedestrians, and doing it quickly.” According to the organization, their members use tactical urbanism to accomplish a range of objectives, including:

Provide a real safety increase for cyclists and pedestrians.

Draw attention to areas of the city that are unsafe for vulnerable pedestrians and cyclists.

Put pressure on the SFMTA and public officials to make proactive, rapid and substantive improvements in street safety.

Many of their interventions involve orange traffic cones, which do grab visual attention but are also impermanent and easily damaged. Adding more robust traffic delineators (also known as soft or safe hit posts) may have helped persuade the city to retain this particular recent installation along John F. Kennedy Drive.

“Generally, we have no choice but to remove cones and posts that do not go through an official process,” wrote the city agency in a statement, “because it’s a code violation to place objects in the roadway, and they could create conflicts for various types of traffic.” But in this case, they plan to install official safe hit posts and leave the temporary ones in place until their review process is complete.

Guerrilla activists in other cities have tried similar things with mixed results. When the group Reasonably Polite Seattleites installed a similar set of delineators along a stretch of road in Seattle, the city initially took them down. Subsequently, though, officials wrote the activists an exceedingly nice response and eventually agreed to reinstall the posts.

City traffic engineer Dongho Chang of the Seattle Department of Transportation explained that a combination of issues (including the height of the posts and state control of the street) forced the removal at first. At the same time, he acknowledged the “time, money and risk” invested by the group and even offered to give the posts back. He later followed up with a letter indicating the city and Washington State Department of Transportation would put the delineators back in place.

In New York City, a perhaps less-polite group has been known to take things even further by building out entire bike lanes from scratch. After a local community board rejected plans to extend an extant lane, Right of Way took to the streets at night to paint their own. As a catalyst, the group cited an accident that took place after a taxi driver struck a pedestrian (after reportedly arguing with a cyclist sharing the lane).

Guerrilla interventions like these can provoke a variety of responses from critics and cities alike. In some cases, tactical urbanists are celebrated by communities but also jailed or fined by officials for their actions. In other instances, though, such installations can give a city an opportunity to publicly support a direction of change. In San Francisco, which has already built out 27 miles of protected bike lanes over recent years, the city seems to be signalling it is open to progress.