Compute modes

The client exposes three ways to compute a human crash-rate baseline. All three run on the same engine and return a rate (per million miles) with a 95% confidence interval, but they differ in geometry and exposure.

Geofence: hb.compute(...)

A county-wide rate, aggregated over Google S2 cells. This is the default mode and is available for every region.

• Numerator: weighted crashes matching your filters.
• Denominator: calibrated vehicle-miles travelled (VMT) across the county.
• Breakdown: result.cells (one entry per S2 cell) for map rendering.

hb.compute(county="travis", ego_vehicle=["cars", "light_trucks"],
           road_type=["arterial", "collector_local"])

Use it for: "what is the human crash rate for cars + light trucks on surface streets in Travis County?" → compute reference

Route: hb.compute_route(...)

A rate over an ordered sequence of interstate (route, milepost) segments. Available for the interstate-corridor regions (see Regions).

• Input: segment_ids, e.g. [("I-35", 250), ("I-35", 251)].
• Denominator: per-segment combination-truck VMT.
• Breakdown: result.segments with per-milepost counts and lengths.

hb.compute_route(segment_ids=[("I-35", 250), ("I-35", 251)],
                 ego_vehicle=["combination"])

Use it for: "what is the crash rate along this stretch of I-35 for combination trucks?" → compute_route reference

Depot: hb.compute_depot_route(...)

A full depot-to-depot trip rate. You give two pins; the engine snaps each to its nearest access cell, picks an on-ramp, routes the interstate leg, and returns a three-leg breakdown (access_a, interstate, access_b) plus a total.

• Input: depot_a and depot_b as (lat, lon) tuples (or dicts/DepotPin).
• Breakdown: per-leg metrics plus access-cell polygons for rendering.
• A pin farther than the snap limit from a known access cell raises a 400.

hb.compute_depot_route(depot_a=(30.25, -97.75), depot_b=(30.40, -97.70))

Use it for: "what is the end-to-end crash rate for a truck running from this warehouse to that one?" → compute_depot_route reference

Choosing a mode

You have…	Use
A county and a set of filters	compute
Specific interstate mileposts	compute_route
Two endpoints (lat/lon) for a trip	compute_depot_route

Mode availability per region is enforced server-side: requesting route/depot for a geofence-only county raises a 400. Always check hb.regions().