It turns out, research has shown, that people dissuaded from a suicide attempt often go on to live full lives.

Critics have challenged both the cost — roughly $210 million in the case of the Golden Gate Bridge — and the aesthetics of such barriers. The money, some argue, might be better spent on mental health services.

For supporters, years of debate have been pervaded by a gnawing urgency over the lives being lost.

So far in 2017, at least 15 people have fatally jumped from the Golden Gate Bridge. Officials don’t expect the nets there to be in place for another four years.

At Coronado Bridge, a perch for roughly 400 suicides since 1969, a person made a fatal leap just a few days ago, said Rhonda Haiston, a Coronado activist who has lobbied for barriers.

In June, Caltrans began a 10-month study on the feasibility of suicide-prevention systems at the bridge. When completed, its recommendations would need to be debated and approved by various agencies.

“We know a lot of people are going to kill themselves in that time,” Ms. Haiston said.