Article Co-Authors – Ilya Ilyankou, Gannon Long, and Anthony Cherolis
Speed humps are a long lasting and relatively low cost method of calming traffic proven to effectively reduce driver speed. Speed humps (with an H) are larger and have a more gradual slope than speed bumps (with a B), their more abrupt cousin.
In the early 2000’s, a move to slow traffic in neighborhoods led to the placement of ninety six speed humps across Hartford. Then in the fall of 2018 through May 2019 the city installed of ninety two additional speed humps. Eighty nine of these had been completed by October 2018.
Transport Hartford’s early analysis indicates that the speed humps have led to lower speeds and safer residential roads where they are installed. Let’s dive into that data!
To see if speed humps increased traffic safety, we pulled all crashes in Hartford that took place between 2015–2019 from UCONN’s Crash Data Repository. Using latitude and longitude data for the precise location of each crash, we measured the distance to the nearest speed hump. We reviewed the number of crashes at these locations that took place in the seven months after the humps were placed, then compared to crash data for the same locations from November 2017 through May 2018. Looking at crashes within a 200 foot radius of speed humps, before implementing speed humps, there were 34 crashes at these spots; four with suspected injury, and another four with suspected minor injury. The following year, with the speed humps in place, there were just 18 crashes, with just three possible injuries reported. That’s a 47% drop in the total number of crashes in 1 season! In the three prior years before the speed humps were installed, there was a relatively consistent number of crashes, and the 2018/2019 period had 49% fewer crashes than that average..
Are other factors responsible for this drop? Throughout 2018 and 2019, centerline crosswalk signs and new fluorescent signs at the edge of the road were placed at uncontrolled crosswalks around the city, alerting drivers to yield to pedestrians. Yet, few of these signs were placed on roads with the new speed humps. While Hartford Police Traffic Division has increased capacity and enforcement, those operations primarily take place on main roads (AKA arterial routes), where the speed humps are not installed. These factors would have minimal effect on the crash rates on neighborhood streets with speed humps..
If alternate factors are contributing to the decline, we would also expect to see a decline in crashes near the previously placed speed humps. At these locations, there were 22 crashes from November 2018 through May 2019. Compared to the same seven month period in the previous three year cycles, when the average number of crashes was 31. This decline of 29% in crashes indicates that while various factors may have decreased crashes on neighborhood streets in Hartford, none are as effective as the new speed humps.
Use the interactive spreadsheet below to see the aggregated numbers of crashes in different time periods for various radii from the speed humps. Note that once the distance is set to over 300 feet, there is a chance that the crash happened on a different block (parallel road) or at a nearby intersection with a busier main road.
The most relevant cell is outlined in black. It represents the number of crashes in the 7 month period following the installation of new speed humps.
Of course, many neighborhood streets don’t have speed humps yet. To further analyze our data, we created a control group of locations similar to where the humps have been placed (primarily residential streets, no major avenues). This way, we obtained another set of 105 points on the map. At these locations, with a 200 foot radius there was an average of 79 crashes over the prior three years. In the 2018/2019 7-month period there were 68 crashes, a 14% reduction. Again, this reduction in crashes is less than the 49% reduction seen for the locations with newly installed speed humps.