Trends in Bicycle Accidents

Trends in bicycle accident-related traffic accidents in the city of Denver, Colorado; from 2012 to 2018. All vector data acquired through the city of Denver’s Open Data Catalogue. Basemap data obtained from Google Maps via QMS in QGIS.

The darkened region of the map shows the extent of ‘Denver proper’ that is, the official city limits of Denver. The northwestern portion of the city limit has been omitted for lack of relevant data.

For the purposes of this study, a bike routewas defined as, by the city of Denver, any road, pathway or lane which has been officially declared a bike route. This includes bike lanes (a seperate lane on the roadway, for cyclists only), shared lanes (an allowance for bicycles to ride in the far right lane of a city road – often not exceeding 30mph / 48kmh), bike paths (a route which is entirely seperate from motor-roadways – for example, the largest bike route in Denver is the Cherry Creek bike path, which follows the Cherry Creek River, as it flows northward through the city, and is not accessible via car). Bikes are not permitted to ride on sidewalks, except where dismounting. The network of roads, their respective speed limits as well as bike routes (referred to in the data catalogue as bike facilities) can be seen below in Map Series 2.

The traffic accident data were aggregated from an initial datapoint count of over 1 million accidents; the datapoints of interest contained at least ‘1’ (and up to 5) in the attribute field ‘BICYCLE’ as listed in the official police report. In Map Series 1 (above), the resulting datapoints are displayed in red, representing all traffic accidents involving at least one bicycle. The green/cyan datapoints highlight those accidents which occurred on a bike route. The orange datapoints, conversely, demonstrate accidents which occurred on ‘non-bike-route’ routes. (*Note – on these maps, the legend should read: ‘Non-Bike-Route Accidents’ and not ‘Non-Bike-Path Accidents’ to avoid confusion with reference to the variation in definitions of bike route vs. bike path)

Additionally, Map Series 1 also displays attributes documented by Denver police where fatalities occured and in which cases there was documented evidence of alcohol or drug use by one or more of the people involved (attribute field ‘OFFENSE_CA’ corresponding with ‘TRAF – ACCIDENT – DUI/DUID’).

Of particular interest, from the visual representation of these data, is the trends in bike-route related accidents and non-bike-route related accidents. With respect to the volume of activity which can be seen in the central business district (CBD) of downtown Denver, a relative correlation to the number of people living and working in this area, as well as the relative correlation to the level of bike activity on bike-routes, the number of accidents may not be statistically signifcant, in terms of comparison to the number of non-bike-route accidents. It is, however, interesting to note the volume of accidents in this particular area of the city in perhaps suggesting that there is a need for more rigorous bike-lane enforcement and general traffic safety. As a cyclist who frequented this area on my daily commute throughout the course of my bachelors program, I collected dozens of images (below) of obstructed bike lanes. It should be noted here that these were, in fact, bike lanes meaning that, in every instance, there was a painted, solid-green lane with either physical barriers (planters, raised curbs, concrete blockades, posts or a designated parking lane seperating the motorway from the bike lane) or a painted white line, dilineating the seperation. In the images I collected, various automobiles, pedestrians, logistcal debree and other larger items blocked the safe use of the bike lanes. In 2018, the bike lanes surrounding Union Station (Denver’s main station), were remodelled and received an upgrade from the painted white lines to a variety of planters and concrete blockades. Data for traffic accidents following this installation were not available at the time of this report (November 2020).

The next point of interest is the bike accidents which occurred on non-bike-route areas. These are notable for several reasons. First, and perhaps the most obvious, being that there is a clear usage of non-bike-route commutes; whether this is a result of ignorance to traffic laws, accidental instances (i.e. a cyclist getting lost) or a general commentary on the nature of safe transportation in the city of Denver is unknown. Secondly, and to speculate reasoning for why these trends exist in the first place; there is a significant presence of what can be referred to as a ‘deliberate’ creation of ‘non-bike-route’ routes. Meaning that there are specific routes which are being used on a regular basis by bike-commuters, occurring in areas which could be assumed to be more accessible/convenient (or potentially the only viable option) in terms of commuting routes, either partly or entirely for a number of commuter’s daily routes. This begs the question of whether the city of Denver should not only invest in making the current bike facilities safer and more accessible, but to expand into other areas of the city, where no reasonable options currently exist. The argument becomes clear when the number of non-bike-route related accidents are demonstrated in the comparison map below.

It should be noted, that the voices of frustrated cyclists are being heard, albeit not nearly as swift as some would hope. In an effort to reduce traffic accidents, the city of Denver has adopted the Vision Zero initiative and has been working towards an app which will allow users to upload images of obstructed bike lanes; resulting from unsafe practices or due to weather conditions to alert commuters, city officials and planners.

Below is a gallery of the maps created for this report.