Speed kills. There is ample research to support the idea that slowing traffic saves lives. Plus, there’s simple physics: A pedestrian hit by a car traveling 20 mph has an 80% chance of survival, but someone hit by a car traveling 40 mph has just a 10% chance.

Nevertheless, a decades-old state law essentially requires cities to set speed limits based on how fast people are already driving, regardless of whether that speed is safe. The law was passed to prevent cities from setting speed traps, or arbitrarily low speed limits aimed at sticking drivers with pricey tickets.

In practice, the law can force cities to set speed limits that contradict their own goals for safer streets, as Times reporter Laura J. Nelson recently detailed. For example, Zelzah Avenue in the San Fernando Valley is one of Los Angeles’ most dangerous streets in terms of the number of collisions that have resulted in severe injury or death, particularly among pedestrians and bicyclists. Yet over the last decade, the city has raised the speed limit on the street twice, increasing it from 35 mph to 45 mph.

The reason for the increases? In order for police to use radar guns or other electronic devices to ticket speeding drivers, cities have to conduct regular surveys of traffic flow. The speed limit is then based on the 85th percentile — that is, the speed just below the 15th fastest driver — and rounded to the nearest 5 mph. The mandate means that if cities want to enforce the speed limit on a street where drivers routinely put the pedal to the metal, they often have to raise the speed limit.

This is a particular problem in Los Angeles. The city fell way behind on its regular speed surveys because of staff shortages during the recession. Without up-to-date surveys, police officers couldn’t use radar guns to enforce the speed limit.

The number of speeding tickets written annually by the Police Department fell from 99,333 in 2010 to 22,783 last year — a 77% drop. With little enforcement, drivers became accustomed to speeding, so when the speed surveys resumed, the speed limits on many corridors like Zelzah Avenue had to be raised.

This is an absurd way to govern a public space. It lets faster-than-average drivers dictate the law, rather than basing the law on what is best for all street users. It doesn’t take into account the community’s broader needs for the street, including making the speed of travel safer for bicyclists and ensuring pedestrians can cross without getting mowed down.

The singular focus on drivers is also contrary to two important movements at the state and local level. California law requires cities and counties to develop so-called Complete Streets that are designed to safely accommodate all users, including cyclists, transit riders, pedestrians and the disabled — not just motorists. And Los Angeles and other cities throughout the state have embraced Vision Zero, which is a campaign to eliminate traffic fatalities and severe injuries by making the streets safer.

The next logical step would be to change the state law that bars cities from setting speed limits for safe travel, rather than just fast travel. But logic doesn’t always prevail in Sacramento. Earlier this year Assemblywoman Laura Friedman (D-Glendale) proposed a modest tweak to the law, allowing cities to take into account collision information when setting speed limits. Under her proposal, if a street was particularly dangerous, the city could reduce the speed limit up to 9 mph below the 85th percentile.

That proved too controversial, especially after a legislative analysis said the change could result in lots more traffic tickets. A watered-down version now calls for a statewide Vision Zero task force to develop policies to reduce traffic fatalities. Still, lawmakers ought to pass Assembly Bill 2363 as a baby step forward.

Certainly, lower speed limits alone won’t make the streets safer. There needs to be public education about the risks of speed, as well as traffic enforcement in speed-prone corridors. Streets also need to be engineered for safety, and that often means redesigning roadways and intersection to make drivers slow down.

Granted, that’s not always popular with drivers who are used to ruling the road. But the streets don’t belong just to drivers. They belong to everyone.