In 2014 and 2017 I did analyses of the bicycle-related research published in peer-reviewed journals. Last month, I needed something to procrastinate instead of writing my TRB paper, so I spent time to update the numbers from 2017 and do some comparisons to pedestrian research. My methods appear that the bottom of this post, and generally follow what I did in 2017.

The growth in bicycle research continues

This time I found 4,365 articles/chapters, up from 2,935 in April 2017. The number of articles in 2018 (504) was only slightly higher than 2017 (501), but the overall trend since 2006 (48) has been strong. The last bar on the chart below is 2019, which obviously is not complete yet. The time lag for articles to show up in Web of Science seems to vary by source, so do not try to interpret that number too closely. Also note that a small share of this overall increase stems from a few newer journals being indexed in Web of Science since 2017. That can increase numbers for previous years.

In my 2017 post, I did some comparisons to other topics, such as electric vehicles and congestion, showing that many transportation topics are increasing at a similar or higher pace. This year I did a parallel search for pedestrian research, using the same search criteria and the terms pedestrian* and walking. There were 20,730 records, with the first article published in 1904 (vs. 1937 for bicycling). The pattern of growth is similar.

And, it is popular.

As I noted in a recent blog post looking at Google Scholar’s journal rankings, bicycle research is popular, at least as measured by citations. The articles in my database were cited a total of 66,335 times. Note that my count (citations*) removes the most highly cited article which turned out to not be the type of bicycle research I wanted to capture and skewed the analysis. That article is “The governance of global value chains” published in Review of International Political Economy in 2005, which used the bicycle industry as one of its case studies. It has been cited 1,960 times, more than twice that of the next article (Handy, S. L., Boarnet, M. G., Ewing, R., & Killingsworth, R. E. (2002). How the built environment affects physical activity – Views from urban planning. American Journal of Preventive Medicine, doi: 10.1016/s0749-3797(02)00475-0). Even still, the distribution of citations is skewed, with a mean of 15.2 citations per article and a median of 4. Some of this is a function of time; more recent articles will not be cited as frequently, as shown in the graph below.

Where is the research being published?

The top journals that are publishing the bicycle research have not changed much since 2017. Transportation Research Record, (the journal of the Transportation Research Board) leads with 506 of the articles, followed by Accident Analysis and Prevention (343). Of note are journals that are rising on the list: Journal of Transport and Health (9^th to 4^th), International Journal of Sustainable Transportation (14^th to 9^th), International Journal of Environmental Research and Public Health (29^th to 19^th), and Journal of Transport and Land Use (41^st to 25^th). Of those, Journal of Transport and Land Use is open source, which is a good sign for access to research. Two journals dropped at least five spots in rankings: Preventive Medicine (8^th to 13^th) and American Journal of Preventive Medicine (10^th to 15^th). It may be that more authors are opting for the newer, more focused Journal of Transport & Health for their health-related work. Finally, the Journal of the Australasian College of Road Safety shows up for the first time because it was not indexed in Web of Science in 2017. In 2017, I had a graph that showed how the sources of the bicycle research have changed over time (by year of publication) and made the point that the sources were diversifying over time. That has continued, as the top 25 bicycle sources in 2017 contained 62% of the articles/chapters, compared to 50% in 2019.

The bicycle research is more concentrated in sources, compared to the pedestrian research. The top 25 journals published 50% of the bicycle articles/chapters, while the top 25 outlets for the pedestrian research included 28% of the over 23,000 articles/chapters. Many of the journals are the same, including the top two. Some of the health journals rank higher in the pedestrian list. There are also some journals that are more focused on the built environment, such as Health & Place, Building & Environment, and Landscape and Urban Planning.

** The source field for my pedestrian search was from Web of Science’s on-line analysis tool, which was different than what I used for my analysis of the downloaded bicycle data. One difference was the handling of conference proceedings. In my bicycle analysis, the source field I used listed the particular conference proceeding at the source title. For the pedestrian analysis, WoS uses a field that has an umbrella title, e.g. Transportation Research Procedia.

Who is doing the research?

In 2017, I was happy to see that my institution, Portland State University, was #2 in the rankings of the organization of the lead author, slightly behind University of North Carolina. I had been hoping we would catch UNC, and we have. But, University of British Columbia is now #1. I’m going to let PSU take partial credit for this, as Alex Bigazzi, one of UBC’s bicycle researchers, is a PSU Ph.D. alum. But larger credit goes to Kay Teschke at UBC, who is one of the top bicycle researchers overall. Another Canadian university, McGill, with another PSU Ph.D. alum (Ahmed el Geneidy) is nipping at our heals in the number 3 spot. The competitive part of me is now motivated to finish some articles over the next year while I’m on sabbatical from my faculty role. Note, the organization is usually based on the lead author’s affiliation, so this does not account for collaborative research. 

The top author remains Susan Handy. Meghan Winters has moved up to eclipse me, which reflects the great work she’s been doing building the CHATR Lab at Simon Fraser University.  Chris Rissel is a professor of public health at University of Sydney.  Eva Heinen at University of Leeds continues to publish strong bicycle research. Another indication of the maturing of field is the second generation of researchers showing up on this list of authors. Meghan Winters worked with Kay Teschke at UBC.  Naveen Eluru is an associate professor at University of Central Florida and former student of Chandra Bhat at UT Austin. Ralph Buehler at Virgnia Tech was a student of John Pucher.

Note: This count includes all authors, not just first authors.

One piece of advice to authors – be consistent on whether you include your middle name or initial in your articles. In my initial posting back in 2017, I had missed that Susan Handy’s work showed up as both SL Handy and S Handy. I fixed that and some similar problems this year, but I’m sure I missed some.

What are we all writing about?

This year I spent some time analyzing the author-supplied keywords for the articles/chapters. To do this analysis I had to make some decisions on combining terms. For example, I converted bike share, bike-share, bikesharing, bike-sharing, public bike share, etc. all to bikeshare. I did this analysis mainly to see if there are any trends over time, and a few did appear. The findings below are based on the percentage of all the keywords for each year, as the number of keywords increased over time. I limited the time period to 1996 to 2019, as there were too few articles with key words before 1996. I also limited my presentation here to keywords that showed up at least 10 times over that time period.

Research on helmets and head injuries is declining as a focus of bicycle research. Those topics represented about 10% or more of the keywords for most years up to 2007, then dropped dramatically.

This shift away from a focus on heads and helmets represents, in part, the growth of the field to focus more on infrastructure and the role of the environment on behavior.

Other topics, including e-bikes, bikeshare, and commuting have also increased, particularly since 2007.

A focus on exercise, physical activity, and recreation was more common in the first decade of the 2000s.

Keywords related to children, school, and youth have fluctuated over this time period.

There is also some evidence of increased focus on gender, equity, and age, though the share of keywords is generally under 2% per year.

What types of research are being cited?

While citations are just one limited measure of impact, it is the one for which I have data. I looked at the trend in the number of times each article had been cited by the first topical category listed for that article. The diversification of the field shows up here as well. The articles from the public, environmental & occupational health field represent a smaller share of citations over time. Ergonomics has also declined. Fields such as economics and transportation have grown.

Conclusions

What does this all mean? As I said in 2017,

I think it shows that the science of bicycling is in very good shape. (It also means that I am easily distracted from what I should be doing this weekend, to analyze geeky data.) When I wrote my first article on the topic (Dill & Carr, 2003) as a new, untenured assistant professor, I did ask myself if bicycle research was the right path to getting tenure. I wasn’t sure, and I developed other, complementary lines of research as well. But, I’m now a tenured full professor, and it’s the bicycle research that has led to a large chunk of my funded research, my most highly cited papers, being called by reporters, appointed to national committees, and, most importantly, the biggest impacts on practice. Transportation engineers and planners are eager to use good research in their work. Because a lot of my work is funded by the US DOT and other public agencies, the findings are usually available in reports, free-of-charge on-line, and not just in journals behind paywalls. So, it can reach the practitioner audience.

That all still holds true. The field continues to diversify with respect to publication outlets and the focus is broadening from injury to topics relevant to questions of why, where, when, and how often people bicycle. These are all good signs, as is the fact that bicycle-related research is heavily cited in the transportation journals.

And, as noted in 2017, “This is obviously a cursory analysis of the research. It would be interesting to do better comparisons to other fields, analysis of funding sources (that data field is poor in WoS), digging more into citations, etc. But, I need to leave it at this for now.”

Addendum

For more on the top cited recent articles and top cited first authors, here is some more.

My Methods

For bicycle research, I followed my same method as in 2017. First, my search uses Web of Science. This is not ideal, but it is currently one of the easier ways to do this type of analysis. Second, one challenge with this search is that the word bicycle and derivations of it are used in medical research to describe physiological processes unrelated to the two-wheeled mode of transportation. Therefore, I limit my search to certain subfields that appear to capture a lot the public health research on bicycling, without most of the unrelated stuff. I did not include some engineering categories, that would capture research on the mechanics of the bicycle but might also capture really unrelated research. I’m also likely missing some of the other social science work.

• Web of Science categories used: planning development, transportation, public environmental occupational health, transportation science technology, engineering civil, geography, urban studies, social sciences interdisciplinary, economics, sociology, history
• TOPIC: (bicycle) OR TOPIC: (bicycling) OR TOPIC: (bicyclist)
• Limited to articles, book chapters, proceedings, and review articles. Excluded: book reviews, corrections, discussions, books, letters, editorial material, art exhibits, retractions.

The process is not perfect. I get a few things that were not about bicycling, but bicycle is in the abstract, for example an article about vaccinations in Zambia that used bicycle ownership as a measure of wealth. But, with about 4,000 records, I did not read every abstract to weed them out, or learn text mining skills to do so. In addition, there are several articles that focused on multiple travel modes, including bicycling. In these cases, since bicycling was included in the abstract, there are likely findings relevant to the mode, so these should be included.