Data sources

National Weather Service

api.weather.gov powers weather forecasts, current conditions, watch/warning alerts, wind direction (the big one for this site), and gridpoint precipitation totals. No API key; we send a descriptive User-Agent per NWS policy.

AirNow (EPA)

airnowapi.org provides AQI and primary pollutant at coordinates. Used when AIRNOW_API_KEY is configured. Cyclists breathe hard — AQ gets heavier weighting here than on most "is-it-a-day?" tools.

OpenStreetMap + Overpass

openstreetmap.org is the canonical source for every named cycling route on the site. At build time we query the Overpass API for every route=bicycle relation across DC/MD/VA/WV/PA/DE, fetch member-way geometry, and compute distance, surface, and traffic-exposure from the way-level surface=* and highway=* tags. We also use Overpass to count cycleway, bike-lane, and multi-use-path length within a 3-mile bubble around each city center — the "bike network within 3 miles" tiles on city pages come from there. OSM map tiles power the route maps.

Wikipedia REST API

Route and city descriptions are pulled from the Wikipedia REST page-summary endpoint when the relevant OSM relation carries a wikipedia=* tag and for every city page. Each summary is cached for seven days; trail and city articles are stable enough that this is rarely a re-fetch.

Nominatim reverse geocoding

Nominatim resolves each route's start coordinates to a state. Used at build time only, with on-disk caching and a 1-second-per-request rate limit per Nominatim's usage policy.

Open-Elevation

Open-Elevation provides the elevation sampling behind each route's profile chart. We densify each polyline, POST up to 100 points per request, and cache the result for 30 days (terrain doesn't move).

NOAA Solar Calculator formulas

Sunrise, sunset, civil twilight, and daylight-remaining are computed locally from published astronomical formulas. No API dependency.

National Park Service alerts

developer.nps.gov provides live closure and advisory notices for every NPS unit. Cycling routes that cross NPS land — C&O Canal Towpath, Capital Crescent, Mount Vernon Trail, Rock Creek Trail, Anacostia River Trail — pull real-time advisories and closure notices from their managing units (CHOH, GWMP, ROCR, NACE). Works with the free DEMO_KEY; set NPS_API_KEY for higher rate limits.

State DOT feeds (experimental)

Every state DOT publishes traffic-event data in a different format — mostly through internal XHR endpoints for their own map apps, sometimes through ArcGIS FeatureServers, sometimes not at all without a developer partnership. Integrations exist for MD, VA, DC, and DE; WV and PA aren't wired in yet. When the known endpoints return data, it appears on the relevant city and route pages; when they don't, those sections silently omit themselves rather than showing stale information. If you know a verified public endpoint for any state, open an issue.

GBFS bike-share feeds

GBFS — the General Bikeshare Feed Specification — is the standardized format most bike-share operators publish. The Capital Bikeshare feed is consumed today and shows live station availability on city pages within its service area. POGOH (Pittsburgh) and Indego (Philadelphia) feeds will slot in the same way.

Generated content

Distance, elevation gain, surface composition, traffic exposure, polyline geometry, and start/end coordinates are computed from each OSM relation's stitched member-way geometry plus an Open-Elevation lookup along the down-sampled polyline. Descriptions follow Wikipedia → OSM description → structured fact summary, in priority order — see the methodology.