NHTSA Fatality Analysis Reporting System (FARS), 2010–2024
Federal fatal-crash database, the source for the “22 people killed in 15 years” figure on our home page. Queried for Arizona (state code 4), Pinal County (21) and Pima County (19), then filtered to a bounding box covering this corridor: latitude 32.50 to 32.85, longitude -111.25 to -110.55, which takes in Oracle Junction through Mammoth with a small margin. Result: 19 fatal crashes, 22 deaths, 2010–2024, on SR 77 inside that box. Two honest caveats. This is a floor, not a total: FARS only records crashes in which someone died, so injury and property-damage crashes are not in it. And the filter is a rectangle on a map, not a milepost range, so “the corridor” here means roughly Oracle Junction to Mammoth (about 27 highway miles), not a surveyed segment. Query API: crashviewer.nhtsa.dot.gov/crashviewer/CrashAPI/crashes/GetCrashesByLocation. Full parameters and the year-by-year breakdown are in our research log. Note that NHTSA’s host sits behind a web application firewall that blocks many automated tools, so a direct link may not load for everyone; that is a quirk on NHTSA’s end, not something we can fix.
ADOT Average Annual Daily Traffic (AADT) 2024
ADOT’s traffic-volume dataset, published as a separate ArcGIS feature service (ADOT_2024_Average_Annual_Daily_Traffic_(AADT), layer 0). Live query: run it yourself. Shows 1,500 to 5,000 vehicles per day through the crash-prone two-lane sections of this corridor: low-to-moderate volume, which is part of why our case rests on crash severity and pattern, not raw traffic count.
ADOT Widening Feasibility Data (2024)
This is a GIS dataset, not a PDF, so there’s no page number to cite. The honest citation is the dataset, layer, and exact query. Source: ADOT’s 2024 Highway Performance Monitoring System (HPMS) Roadway Data, published via AZGeo/ArcGIS Online (item ID e37ef1a66267449da93400c61c529f8a), layer Widening_2024 (layer 60 of 63 in the HPMS_2024_Data FeatureServer). Live, checkable query used: run this query yourself. Re-confirmed live 2026-09-13, results unchanged from when first found.
Note: ADOT’s internal GIS “Measure” field for this dataset runs 68 miles low of the real signed highway milepost (Measure 0 = real MP 68 at I-10 in Tucson). Both are shown below.
| Real milepost | ADOT internal measure | Feasibility | Obstacle noted | Lanes feasible |
|---|---|---|---|---|
| 103.7–108.1 | 35.7–40.1 | Yes, 2 lanes | None | 2 |
| 108.1–112.5 | 40.1–44.5 | Yes, 2 lanes | Terrain restrictions (near San Manuel turnoff) | 2 |
| 112.5–114.2 | 44.5–46.2 | Yes, 2 lanes | Dense development (near Mammoth) | 2 |
| 114.2–133.6 | 46.2–65.6 | Yes, 3+ lanes | Terrain restrictions | 3 |
What this does and doesn’t show (added 2026-09-13). We used to feature this rating prominently. After checking the layer’s own documentation and the statewide numbers, we’ve reframed it, and we’d rather explain that than quietly move on. By ADOT’s own description, this layer records “the potential to widen a road and add more lanes as well as any barriers on the side of the roadway that would prevent widening”: it measures physical constraints like terrain, right-of-way, and adjacent development. It does not measure whether a road needs widening. And a “Yes” is common: of the roughly 5,400 Arizona segments that carry any rating at all, about 82 percent get some form of “Yes” (only about 18 percent are rated “No widening feasibility”), and most of the network has no rating in this layer because it only covers the sample sections FHWA requires ADOT to report. Check the statewide breakdown yourself. So the fair reading is narrow: ADOT’s own engineering data rules out “this road can’t physically be widened” as an objection for the Oracle to Mammoth stretch. It is not, by itself, evidence that this stretch should be prioritized. The evidence for that is the crash record above and the crash-type detail we’ve requested from ADOT.