Harvard stairwell experiment

The Harvard stairwell experiment was a simple intervention by Thomas Schelling that transformed a recurring traffic jam into an unspoken convention. By asking his 10:00 AM class to use the front stairwell when going up and the rear stairwell when going down, he set in motion a pattern that the neighboring classes adopted without explicit instruction. The example illustrates how coordination can emerge through a modest change in behavior rather than centralized command.

The problem in the building

When Schelling taught in a second-floor classroom at Harvard, students crowded into both of the building’s narrow stairwells during breaks. Each stairway carried people moving in both directions, so students had to jostle past one another. The difficulty was practical and recurring: people needed to move between floors, but no shared arrangement directed the flow.

The two stairwells offered an obvious way to separate traffic, but students had not independently established a consistent convention. Rather than impose a formal rule on the building, Schelling used his class as the starting point for a change in the pattern of movement.

A small intervention and its spread

Schelling asked his 10:00 AM students to take the front stairs up and the back stairs down. The instruction applied to that class, but it changed the traffic pattern encountered by students arriving before and after it. According to Schelling’s account, within about three days the 9:00 AM class had learned to go up the front stairs, while the 11:00 AM class came down the back stairs. As far as he knew, neither class had been explicitly instructed to do so by the 10:00 AM students.

The arrangement thus extended beyond the group that received the initial request. A limited, concrete adjustment became a shared practice across successive classes, organizing movement in both directions without a building-wide order.

Coordination without command

The experiment exemplifies Schelling’s broader account of coordination: groups can sometimes reach a workable solution when people’s behavior supplies a pattern others can recognize and follow. The change did not depend on a central authority enforcing a permanent rule. Schelling’s interpretation was that the later classes accommodated themselves to the altered flow.

The stairwells also show how conventions reduce the effort required to coordinate. Once people treat one route as the way up and the other as the way down, each student need not negotiate afresh with every person coming the other way. In the book’s argument, the episode makes visible the practical force of a convention: a small change can help otherwise unconnected people organize their actions with less conflict and without continuous supervision.