2015_12_17_CIE_experimento

Researchers from department of Physics and Applied Mathematics at the University of Navarra have demonstrated for the first time with real experiments what happens in a traffic jam when people push each other, a variable that had not been measured in any previous study.

The experiments - conducted at partnership with the School of Architecture and the Sports Service of the academic center - used pressure sensors and three cameras to record what happens when a group of people - one hundred volunteers in this case - try to exit at the same time through a door. The experiments were conducted with 68 cm and 75 cm doors and ten recordings were made at status of no pressure, average pressure and high pressure.

The results obtained indicate that the greater the thrust, the greater the pressure at the outlet and the more traffic jams occur. "And not only that," explains Iker Zuriguel, the researcher who led the experiment, "but also the difficulty of undoing these jams gradually increases. In fact, we found that with pressure, the probability of generating one-second jams increases tenfold. This is very important if we take into account that a 3 or 4 second traffic jam can be life-threatening for people".

The group of laboratory of Granular Media at the University of Navarra has been working for several years on the way in which different agents behave at the exit of an enclosure - from grains or particles in silos to sheep in a flock - but until now it had not been possible to extrapolate to people. "The application internship of this study is wide, but perhaps one of the peremptory measures could be to modify the current regulations on enclosure exits, which are designed and calculated without taking into account the determining factor of pressure."

Same time, but more accidents

The recordings made for the first time with people also show that it is not only the time it takes to evacuate an area that needs to be taken into account, but above all the frequency with which bottlenecks occur in the process: "The programs of study that has been available up to now focuses exclusively on the time it takes to evacuate an area, but very different circumstances can occur at similar times, as can also be seen in the videos we have made. Traffic jams that are shown as small jumps in the graph can result in more or less serious and even fatal accidents".

To date, the group at department of Physics and Applied Mathematics of the University of Navarra has performed more than 600 evacuations with sheep. With them they have proven the usefulness of placing an obstacle in front of the exit door to reduce the thrust pressure. The next step will be to demonstrate the consequences of placing an obstacle with people, which would have important practical applications in all subject enclosures.

The work, published in the scientific journal Physical Review E, has been carried out in partnership with the committee National Scientific and Technical Research of Argentina (Conicet) and the School of Veterinary Medicine of the University of Zaragoza.