When it comes to public buses and the spread of airborne particles, some seats may be better than others.

Experts at IBM Research took a systematic approach to something many bus riders probably wonder: Where and how far do exhaled droplets from other passengers travel? To answer that, the researchers developed a model with an unprecedented level of detail that focused on the physics of air and droplet dynamics, as well as environmental factors that affect their spread.

They analyzed what happens when speech droplets are exhaled from a row of seated passengers in a ventilated space — much like the environment on a bus or other public transportation. They also created a ventilation pattern found on many forms of public transit. Typically, that means air is injected near the top of the vehicle and removed near the bottom through vents close to window seats.

Various transmission scenarios were replicated by placing passengers in different seats and having them pronounce a vowel for a few seconds. That allowed the researchers to create a “flow field” and track individual exhaled droplets and their ventilation paths.

This is what they found: Droplets exhaled from a window seat rose more but were less likely to invade other passengers’ space. Droplets from middle-seat passengers were more likely to invade aisle passengers’ space. Droplets that originated from the aisle were dragged down by the ventilation system almost immediately.

The researchers hope their findings will one day be applied to designing better ventilation systems on public transit. For now, this much is certain: The less you talk on the bus, the fewer airborne particles you’ll spread.