A course in crowd science and crowd safety
How crowds flow, and why they crush.
Density, speed and flow; the physics of force in a packed crowd; what people actually do in emergencies; the models engineers trust; and the disasters that taught the field what it knows. Built for someone who likes numbers and wants to become genuinely expert.
Numbers you will be able to defend
Crowd safety runs on a handful of quantities. By the end you will know each of these, where it comes from, how sure anyone is, and what to do with it.
- Mean free walking speed across 52 published studies
. Module 1, lesson 2 - 1.34m/s
- The most a corridor passes per metre of width on Weidmann’s curve, reached at 1.75 p/m²
. Module 1, lesson 3 - 1.23p/m/s
- The Green Guide’s rate of passage on level routes; 66 on stepped ones
. Module 7, lesson 3 - 82p/m/min
- Marcel Altenburg’s projected busiest finishing wave at the New York City Marathon, and the reported actual
. Module 5, lesson 2 - 1,366/ 1,367
Nine modules, one arc
The order is deliberate: a feel for density, then how density hurts, how people actually behave, and how we model it. Then the marathon thread, with real tools in hand; evacuation; event practice; and finally the case studies.
Case studies come late on purpose. Read Hillsborough first and you learn a tragedy. Read it after the first seven modules and you see pens over capacity, a gate opened without flow control, compressive asphyxia, and the panic myth in the press coverage.
If you came here through Start Right
Marcel Altenburg, Senior Lecturer in Crowd Science at Manchester Metropolitan University, models mass-participation races. His university describes Start Right as “a unique mathematical algorithm to help race organisers visualise the flow of runners through the entire course”
No peer-reviewed description of the method has been published. So module 5 does the honest thing: it builds a model of the kind Start Right must be, labelled as our reconstruction, and hands you a wave planner to run a 40,000-runner start yourself. By then you will have the flow theory to know why it works.
4 → 6
How every lesson works
- Intuition before formulasEach idea starts with a picture or an interactive, then the words, then the equation, then a worked example with real numbers.
- Interactives where they earn their placeTwelve of them, from a density visualiser to a marathon wave planner. Each tells you what to try and what you should notice.
- Check yourself as you goShort free-text questions with model answers mid-lesson, then a quiz with explanations for right and wrong answers.
- A review queue that remembersQuestions you miss come back first; ones you get right return after three days. All stored in your browser.
- Every number has a sourceEach figure links to the paper, report or page it came from. Where sources disagree, the lesson says so.
- Respect for the people involvedDisasters are taught for prevention: mechanisms, decisions and inquiry findings, never blame of the crowd.
Your first step
What is a crowd? Space, bodies and the number that matters
Why a full lift is dense but safe, what 2, 4 and 6 people per square metre look like, and why the dangerous thing about a crowd is not its size. About 35 minutes, with an interactive density visualiser.