Google Scholar just released their 2019 Scholar Metrics, so of course I am distracted from what I should be working on. Google bases the rankings on the h-index for articles published in the last five complete calendar years. I was curious what topics are cited most often, so I looked at the top 20 articles for 15 of the top 20 transportation journals and assigned a single topical category to each. It wasn’t a perfect process. Most of the time I made the call based on the title only. A few times, particularly for topics outside my area, I looked at the abstract. Many articles cover more than one topic. I tried to capture the main topic, focusing on modes firstly. I’m sure if someone else did it the numbers would be slightly different. I skipped the journals that did not appear to cover a range of topics and that, quite frankly, I wasn’t very interested in. (This is a blog post, not a journal article; I can be arbitrary.) Table 1 has the list of journals and the top topic I identified in the top 20 articles. Table 2 shows the overall totals for all 300 articles. I also created a figure that shows all the data, but it’s not ideal, given the number of categories.

Not surprising, autonomous vehicles (AVs), connected vehicles (CVs) and related topics (e.g. adaptive cruise control, collision awareness systems, etc.) came out on top, representing 17% of the articles and the most popular topic in five of the 15 journals (based on the 20 most cited articles). That was followed by bicycling, including bikeshare and e-bikes (11%), freight and logistics (10%), electric vehicles (9%), and travel demand/behavior (9%). And to clarify, if an article looked at the travel behavior of people on bicycles for example, I labeled it a bicycling article. The “travel demand/behavior” articles were not mode specific.

My quick observations:

• Bike research is popular. There is at least one bicycle article in the top 20 in 10 of the 15 journals. (CVs/AVs and EVs also showed up in 10 journals.) Here is a list of all 33 bike papers.
• Pedestrian research is not. There was only one article (of 300) focused on pedestrians, so it ended up in “Other.” There was also one article on drones. More travel happens on foot than drones.
• Some topics that I assume were highly cited a decade ago are no longer, such as land use and pricing. Does this mean they are less relevant today? that we aren’t doing as much research in these areas now? that we know what we need to know?
• While I placed articles focused on equity across modes into the category of “planning/policy/equity” the topic of equity was found in several other articles, e.g. equity and bicycling, transit, etc.
• Transportation Research Record is ranked #14, which is good to see. In case you have not heard, the journal is moving to an editorial model more akin to other journals, not completely tied to the annual conference. You’ll be able to submit articles there throughout the year, for example, and publication reviews will be done separately from the conference. One goal is to continue the journal’s trend of improved quality.

If you do have a few minutes to spare, and want to find some new articles to read, take a look at the top journals in Transportation. You might find something new to cite.

Table 1: Google Scholar’s top Transportation journals (within Engineering category)

Table 2. Main topics overall among the top 20 articles in each journal

Figure 1: Top topics in the top 20 articles in the 15 journals

p.s. I also looked at the top 20 articles in the Journal of Transport & Health and found that 12 of them are on bike/bikeshare. That journal is probably not in the Transportation category in Google, but would not have made the h5-index cutoff for the top 20 journals. It is 30 for JTH and 33 for the 20th Transportation journal. Those 12 articles are on the list of all 33 bike papers. Full disclosure: I am on the editorial board of JTH.