Switching off street lights at night seems to be reducing crime...

A recent petition calls for Surrey County Council (SCC) to discontinue their policy to switch off street lighting at night. The petition and includes data from a freedom of information request on crime statistics for 2015, 2016 and 2017. The author of the petition claims that these data demonstrate that crime has increased as a direct result of SCC's decision to switch street lighting being switched off. 

I'm a scientist and I can't help analyzing interesting data when it's put in front of me, and I wanted to verify that the claims are accurate. Here are the results of my analysis, which seem to suggest that not all is as it seems...

Firstly, I found that, across Surrey, the data reveals that crime has increased significantly in 2017, which is very worrying, and there are doubtless a large number of sociological reasons for this.

However, we are specifically interested in whether there has been an increase in night-time crime, caused by the street lighting changes. I'm calling 'night' the period between 12pm and 5am (when street lights are off) and 'day' as the rest of the time (5am to 12pm). As 'night' here is only 5 hours long and 'day' is 19 hours, I have calculated the increase in the number of crimes per hour (since 2015) to try and take this into account (obviously there will be other differences between these two periods). 

As you can see in the first graph (below), the average number of crimes per hour during the day and the night have both increased since 2015 (up by 1.4% per hour in the day and 0.8% per hour at night). 

It is interesting to note that the increase in night-time crime is much smaller than the increase during the day (the difference was statistically significant, if that’s of interest to you). Daytime crime has increased at almost twice the rate of night-time crime. You would expect that, if street lighting was having a significant impact on night-time crime rates, then the increase in night-time crime would be greater than the increase in daytime crime. However, day and night are very different when it comes to crime, so it is difficult to draw solid conclusions from this.

Data was also provided showing how long each borough has had its lights switched off for, which is particularly useful. My second graph shows the number of months each Surrey borough has had its lights switched off for, against the percentage increase in night time crime rate in 2017. You would expect that, the longer a borough has had its light switched off for, the greater the increase in night-time crime. If anything, it actually shows the opposite: the longer a borough has had its lights switched off for, the lower their increase in crime rate. 

This suggests that, rather than increasing crime, switching off street lights between 12pm and 5am could actually be reducing crime.

This result could seem counter-intuitive, but is in keeping with several studies that show a similar result (an interesting summary can be found here: https://www.citylab.com/equity/2014/02/street-lights-and-crime-seemingly-endless-debate/8359/). It seems that street lighting has the effect of making us feel safer, without actually improving our safety.

These are small numbers of data, so it is difficult to draw concrete conclusions, and we don’t know what types of crimes are being committed at night and day, or if it changes between years. However, my analysis does suggest that the data does not seem to support the conclusion that SCC’s policy of switching of street lights has caused an increase in night time crime – rather, it seems to imply the opposite.

My analysis suggests that the financial (and presumably, environmental) savings that are being made by switching off street lighting at night currently appear to be safe and justifiable, and have not resulted in an increase in night time crime (and may have actually reduced crime). Whether this trend continues will be important to monitor, but currently focusing on street lighting as the cause of increased crime rates could distract from the real factors that are underpinning it.

Here is a link to the data: https://www.dropbox.com/s/4oh5xhey1386rt3/streetlights.xlsx?dl=0