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30 Minutes From Help — time-of-day drive-time catchment of Port of Spain General Hospital https://tt-hospital-30mins.vercel.app
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GregM febf56a2af Log personal-utility rework in work tracker 
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-07-31 18:55:59 -04:00
scripts 30 Minutes From Help: isochrone scrollytelling MVP for Port of Spain General Hospital 2026-07-31 18:05:52 -04:00
site Address personal-utility gaps: address lookup, corridor names, OG card, softer precision 2026-07-31 18:53:05 -04:00
lessons_learned.md 30 Minutes From Help: isochrone scrollytelling MVP for Port of Spain General Hospital 2026-07-31 18:05:52 -04:00
next_steps.md Log personal-utility rework in work tracker 2026-07-31 18:55:59 -04:00
README.md 30 Minutes From Help: isochrone scrollytelling MVP for Port of Spain General Hospital 2026-07-31 18:05:52 -04:00
work_log.md Log personal-utility rework in work tracker 2026-07-31 18:55:59 -04:00

README.md

30 Minutes From Help

A scrollytelling data story: how far can you be from Port of Spain General Hospital and still reach it within 30 minutes by road — at four different times of day?

Live: deploy site/ to any static host (Vercel/Cloudflare Pages).

The four time periods

Period Window Modeled avg speed vs free flow Effective budget
Night after 9 PM 100% 30 min
Midday 11 AM – 2 PM 75% 23 min
Morning rush 6:30 – 8:30 AM 50% 15 min
Afternoon rush 4 – 7 PM 42% 13 min

Result: the 30-minute catchment collapses from 159 km² at night to 20 km² at afternoon rush — about 13% of its nighttime area.

Methodology

  • Isochrones: reverse drive-time polygons ("from where can you reach this point?") to POSGH (10.6619°N, 61.5078°W), computed on the OpenStreetMap road network via the public Valhalla instance at valhalla1.openstreetmap.de.
  • Time-of-day model: Valhalla routes at baseline speeds; public historical traffic data for Trinidad does not exist. Each period scales the 30-minute budget by an average-speed factor (table above) drawn from reported commuter experience for the capital (ECLAC/IDB congestion studies; 4–7 PM is the reported worst window). These are transparent estimates, not measurements.
  • Stats: polygon areas via planar shoelace on an equirectangular projection; place reachability via point-in-polygon over 33 named communities.

Repo layout

  • scripts/fetch-isochrones.mjs — fetches/derives all data → site/data/isochrones.json (no deps, Node 18+)
  • site/ — static site: MapLibre GL + OpenFreeMap dark tiles, vanilla JS scrollytelling, no build step

Develop

node scripts/fetch-isochrones.mjs   # regenerate data
python3 -m http.server -d site 8741 # preview

Sources