San Francisco District 9 supervisor Hillary Ronen sent a letter to ride-hailing giants Uber and Lyft Tuesday, asking them to use geofencing technology to find safe places for pick-ups and drop-offs — and to test such a system on Valencia Street, notorious for ride-share cars blocking the bike lanes.

“At this point, Valencia is completely out of control with bikes, cars and pedestrians struggling to safely navigate the street,” the letter reads.

Geofencing would tell passengers where to go for a safe pick-up and directs the car-share driver to that location.

The letter asks the companies to work with the city to identify places for the cars to pick up or let out passengers, and to enforce that use of the technology.

Ronen pointed to the size of the street and driver behavior as causes of the driver-cyclist conflicts.

“The lack of space on the street forces your drivers to break the law and block the bike lane when they drop off or pick up their customers,” Ronen wrote, also alluding to “your drivers’ disregard for existing traffic and parking regulations.”

Rec and Park officials have already said that the drop-off and pick-up activity at Dolores Park clogs the area around 19th and Dolores streets. On Valencia Street, drivers are competing with the bike lanes — and the concentration of rideshare traffic on Valencia is much higher than on neighboring Dolores.

Though Ronen voiced support for infrastructure changes — like protected bike lanes — that would physically bar cars from entering the bike lanes, she noted in her letter that such a project would take time, study and funding to complete.

Her letter was sent hot on the heels of another letter from San Francisco Mayor Ed Lee to the ride-sharing companies, asking them to participate in a pilot program testing dedicated ride-share parking spots.

Lee proposed having Lyft and Uber share anonymized travel data with the city to help it understand traffic patterns. Along with the dedicated parking spots, the proposal also includes geofencing to restrict pick-ups and drop-offs in dangerous areas.

A pilot corridor to test Lee’s proposal has yet to be identified, and an aide for Ronen suggested that Valencia would be a good candidate.