Does closing the Great Highway cause an increase in traffic accidents?

By Robert Ellison. Updated on Tuesday, July 23, 2024.

A car speeds on a beach

There is some debate in San Francisco at the moment around permanently closing the Great Highway to traffic.

This road was closed during the pandemic and I regularly visited with my kids to enjoy a bike ride in a safe and beautiful environment. There were also 'slow streets' dotted around the city, many of which persisted. These still have cars and parking and are much less compelling.

Opponents of the plan are concerned that traffic displaced from the Great Highway will make neighborhood streets more dangerous. The hope is that this traffic will shift to Sunset Boulevard but the reality is likely some increased traffic in the Outer Sunset. This seems like a reasonable complaint, but so far I haven't seen any data. Since August 2021 the Great Highway has been closed weekends, holidays and Friday afternoons. Is it possible to see the impact?

I downloaded injury accident and fatality data from Data SF.  This covers the entire city so I first cut the data set down to an area bounded by the Great Highway and Sunset Boulevard (including both) and Lincoln Way and Sloat (excluding both). I then picked a pre period from May 28, 2017 to February 29, 2020 and a post period from September 1, 2021 to June 4, 2024. Both periods are 1,008 days which is 36 28 day periods. Here's a chart of injury accidents (number of people injured in total) by week day:

The good news is that injuries are down overall. Monday through Friday the total decrease is 26%. When the Great Highway is closed at the weekend the number of injuries decreases by 44%. It looks like the streets have got safer when the Great Highway is closed. Before the pandemic you would be 14% more likely to get injured at the weekend, for the last few years this has flipped to 14% less likely.

I also looked at deaths. There are only two, both in the post period. One was on a Saturday and one a Monday. That's not enough data to try and draw any conclusions.

Given how nice that stretch of road is, I'm now a big supporter of the Great Highway Park concept.

In case it's useful here's the code behind the analysis:

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(Published to the Fediverse as: Does closing the Great Highway cause an increase in traffic accidents? #politics #sanfrancisco #greathighway Analysis of data from DataSF shows injury accidents are lower when the Great Highway is closed to traffic. )

Comments

D.S.H.

It cuts off Daly City, Pacifica, etc from the city of SF. Already enough trouble and traffic from closures in Golden Gate Park!

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