Does it feel like the cops aren’t really doing traffic enforcement anymore?
Last week I read this comment about MPD not enforcing traffic violations and it inspired me to look at some data I’ve been analyzing over the past few weeks. I pulled more than seven million moving violation citations from DC Open Data‘s API. This is part of an ongoing project to sharpen skills using Python for data wrangling and visualization.
I found that the average number of monthly traffic stops by live officers took a nosedive during the pandemic–and haven’t returned to pre-pandemic levels. Not a surprise for anyone who has ventured out for a walk, bike, scoot or a drive in the last couple years.
This chart shows the count of monthly citations issued by the city’s 138 automated traffic enforcement (ATE) cameras (in red on the right axis) against citations issued by other means (in blue on the left axis). My assumption is that these citations are traffic stops made by officers of MPD and the 40 or so other agencies reporting this data to DC DMV (including the Park Police, Capitol Police, Secret Service, and some other interesting outliers I’ll post about on Twitter).
The two horizontal lines represent the historical averages before and after the onset of the pandemic. From January 2017 to the end of March 2020 the average number of traffic citations issued per month by a human was 6,127. In the period from April 2020 to the end of 2021 that number was 2,922 — a 52% decrease.
In contrast the ATE cameras actually increased their monthly count from an average of 101,427 pre-pandemic to 120,419 in the aftertimes. This may be explained by new ATE cameras being deployed, although the press office at the District Department of Transportation only has press releases announcing eight new cameras in June 2021.
To check if the drop off in traffic stops might have been a function of lower traffic volume I grabbed data from the Federal Highway Administration. They provide a monthly estimate of traffic volume across the country, collected from continuous traffic counting locations nationwide. Although this data is reported by ‘the States,’ the District of Columbia is also included.
Dividing each month’s mean of traffic stops from the moving violations dataset by each month’s traffic volume gives a useful metric of traffic stops per unit of traffic volume. The pre-pandemic mean of stops per unit of traffic volume was 19.84; post-pandemic onset the mean dropped to 15.96 — a drop of nearly 20%.
The data does have its issues. You can see that no data at all was issued for February 2017. Also 2022 has been omitted from the analysis because my methodology for identifying ATE-issued tickets requires the first character of the ticket number. The evidence, however, looks strong that MPD and other law enforcement organizations have not returned to pre-pandemic traffic enforcement levels, automated systems not withstanding.