It was with a heavy heart that I learned that my PhD advisor Dr. Yili Liu has passed away. Yili was my PhD advisor at the University of Michigan from 2009 to 2015, who has made a fundamental impact on me as a researcher and as a person. I remember in the early years of my PhD I was not used to our meetings in which Yili rarely gave me specific tasks, but rather, he kept asking me, what do you want to work on? what are you passionate about in your research? I remember back then I was thinking to myself, it would be much easier if you just tell me what to do. Until years later when I started my own academic journey as a faculty, I realized the important lessons Yili has taught me all along about following your passion in research and taking initiatives. He directly inspired me to shift my research areas over the years and now around something I care deeply about - the safety of people walking and bicycling and how we can evolve from a car-dependent society.

Yili was fun to work with. When a PhD student graduated from our group, Yili set up a tradition of having dinner at a restaurant with its name in alphabetical order. According to John Murray, Yili’s first PhD student graduated in 1996, they had the graduation dinner at the (now closed) Argiero’s in Kerrytown, hence the start of the letter sequencing. I was letter P. We were joking that we will just walk to Panda Express in Pierpont if the work was not good. We ended up going to Palio on Main Street, so I guess I did okay. 

Yili and I kept in touch over the last ten years after my graduation. Whenever I needed career advice, he was always available and one phone call away. Sometimes we decided to talk at a restaurant, and we tried to stick to restaurants starting with a P whenever we can (Pacific Rim). Yili continued to guide me through my faculty search and then as a junior faculty at UM-Dearborn. To the contrary of the often vague advice he gave me about what research to conduct, he always gave honest and direct advice on career-related questions that I have for him. Although sometimes that was not the answer that I was hoping to hear, but deep in my heart I knew he was right.

The last time Yili and I talked was early 2025 when I invited him to a seminar talk on the UM north campus that I was giving. Yili was not able to make it, but asked me to share the recording of the talk with him. It will be a forever regret of mine that I never got to invite him over to our place to catch up and personally meet my family after we moved back to Ann Arbor. I always thought, we have time, and we will do it soon when we are less busy. But sometimes we will never be able to. I will forever be grateful that I got to know Yili and have him as an advisor, colleague, and a dear friend.

P.S. A memorial for Dr. Yili Liu was held on January 27, 2026 at the north campus of the University of Michigan, Ann Arbor. Some photos at the event can be found below.

You can find the presentation slides below.