The Bloomington community is mourning the loss of Dr. Mark A. Dayton, 70, a respected cancer treatment specialist with IU Health Hematology & Oncology, who was killed in a bicycle accident on August 11.

Authorities say the crash occurred around 1 p.m. at the Judah intersection of Indiana State Road 37 and Old Ind. 37 in Lawrence County, about 15 miles south of Bloomington.

According to a preliminary police report, a 26-year-old Mitchell man driving a 2012 Chrysler 200 southbound on Ind. 37 ran a red light at the busy intersection, striking Dayton as he crossed the highway on his bicycle.

Witnesses told police that Dayton, who lived near Lake Monroe in southern Monroe County, was riding west on Old Ind. 37 and had the green light. He was pronounced dead at the scene.

The driver, who was not injured, voluntarily submitted to a blood draw to test for alcohol or drugs—standard procedure in fatal crashes. Results have not yet been released. The Indiana State Police sent an accident reconstruction specialist to the site, and the investigation remains ongoing.

Dayton’s death has left a deep void among his patients, colleagues, and community members. A dedicated physician, he was widely known for his expertise in cancer treatment and his compassionate approach to patient care.

His work at IU Health touched countless lives, offering not only medical skill but also comfort and hope to those facing serious diagnoses. Beyond his medical career, Dayton was an active member of the Bloomington North Rotary Club for 18 years.

Club members described him as a passionate advocate for peace, health, education, and social justice. In the past year, he delivered two presentations to the club, offering thoughtful analysis on the state of America’s healthcare system under both the Biden and Trump administrations.

“We are so privileged to have known Dr. Mark Dayton,” the Rotary Club said in a statement. “His impact is immeasurable in our community. Please honor his commitment to peace, health, education, and social justice.”

Friends and colleagues recall Dayton’s sharp intellect, deep empathy, and tireless dedication to service. Whether in the clinic, at Rotary meetings, or in personal interactions, he was known for listening carefully, speaking thoughtfully, and acting with integrity.

The crash location—near the Johnny Junxions service station—is a heavily traveled area where Old Ind. 37 crosses four lanes of high-speed traffic on Ind. 37. Safety advocates have long noted the risks for cyclists and pedestrians at such intersections, where visibility and driver attentiveness are critical.

For many, Dayton’s death serves as a stark reminder of the vulnerability of cyclists on public roads. Advocates are urging drivers to exercise heightened caution, especially at intersections, and to remain aware of those who share the road.

As the investigation continues, Dayton’s family, patients, and friends are left grappling with the sudden loss of a man whose life was defined by service and compassion. In the words of one Rotary member, “Mark was not just a healer of bodies—he was a healer of communities. His absence will be felt in ways we can’t yet measure.”

Funeral arrangements have not yet been announced. In the meantime, those who knew Dayton are encouraged to honor his memory by supporting causes he championed and embodying the values he lived by—kindness, service, and the pursuit of a healthier, more just world.