Service Accessibility Calculator
How many people a facility — a clinic, a library, a school — serves within a travel-time threshold, and how many facilities a district needs so everyone is within reach.
A facility serves a circle of radius equal to the travel time times the travel speed, divided by the street detour.
How the service accessibility calculator works
A facility serves a circle of radius equal to the travel time times the travel speed, divided by the street detour. Population within it is that area times density. The facilities needed for full coverage are the district area divided by the coverage circle, with overlap.
The threshold is a policy choice: 15 minutes' walk for a primary school, 30 minutes' drive for a hospital. This takes it as an input.
Formula: reach = time × speed / detour; facilities = district area / (π reach²) × overlap
Worked examples
| Inputs | People served by one facility | Note |
|---|---|---|
| A 15-minute walk | 10,166 | about 12 facilities needed |
| A 10-minute drive | 162,656 | one facility covers the district |
| Denser | 26,141 | each serves more people, same count needed |
FAQFrequently asked questions
What travel time should I use?
The one your policy sets: 10 to 15 minutes' walk for schools and local shops, 30 minutes' drive for a hospital. It is a choice, not a fact.
Why the 20% overlap?
Because circles do not tile and districts are not round. Real coverage needs more facilities than the pure area division.
How does this differ from the transit catchment page?
Same geometry, different question. That page asks who reaches one stop; this asks how many facilities reach everyone.
Does speed matter that much?
It is the whole difference between walking and driving. At 30 km/h one clinic covers what takes twelve on foot.
What about people without a car?
Run it at walking speed for them. The gap between the two answers is the equity problem.
Where these figures come from
- UN-Habitat — Urban Indicators Guidelines — density, green space and public space benchmarks
- World Health Organization — Urban green spaces — the 9 m² per person minimum
- ITE — Parking Generation Manual — parking demand rates by land use
- US Census Bureau — Population and housing — the US national statistics agency
Last checked: September 2026. Default per-capita rates are mid-range figures from national statistical agencies and utility reports; every one is an input you should replace with the local figure.