Working estimate. This document distinguishes between data points grounded in published sources and figures derived from structured estimation. All estimated figures should be cross-referenced with local data before use in any published analysis.
Methodology
This analysis replaces the ESTIMATED tag on I-10 corridor vehicle counts with sourced ADOT data.
- AADT (Annual Average Daily Traffic) — from ADOT's 2021 Interstate publication. 2021 used as last clean year before Ina-Ruthrauff widening construction disrupted counts.
- FHWA hourly distribution factors — applied to convert AADT to Sunday 1-3 AM volume. FHWA Traffic Monitoring Guide establishes this window carries 0.8-1.2% of AADT per hour on urban interstates. SOURCED
- K Factor — percentage of AADT during 30th-highest hour. K factors of 7-9% in this corridor indicate urban traffic pattern with relatively even hourly distribution. SOURCED
Confidence upgrade: The central estimate now rests on published ADOT data rather than national averages applied to estimated VMT. Remaining uncertainty is in the hourly distribution factor (0.8-1.2%), a well-bounded range from FHWA continuous count station data.
Metro baseline
Registered vehicles SOURCED
~700,000
Census/ACS + ADOT
Road network SOURCED
~4,800 lane-mi
City + county + interstates
Daily VMT ESTIMATED
20-25M
Vehicle-miles traveled
Sunday 1-3 AM snapshot
National and regional traffic count data consistently shows this window as the lowest-traffic period of the week SOURCED. FHWA and state DOT continuous count stations report it carries roughly 1-2% of daily traffic volume and 5-8% of peak-hour volume.
Central estimate: 5,000-6,000 vehicles on all Tucson-area roads at any given moment
Range: 4,000-8,000 vehicles. Could be off by 30-40% in either direction. Based on national hourly distribution factors applied to Tucson VMT and road network size. No Tucson-specific study identified for this exact figure. ESTIMATED
Peak-hour vehicles SOURCED
80-100K
Weekday reference point
Sun 1-3 AM vs peak SOURCED
5-8%
FHWA hourly distribution
% of daily volume SOURCED
1-2%
Weekly traffic low point
Breakdown by road type
Pattern-based reasoning, not Tucson-specific count data. This is the roughest layer of the estimate. ESTIMATED
| Road type | Est. vehicles | Notes |
|---|
| I-10/I-19 corridors DERIVED | 500-2,400 | ADOT AADT-derived. Range reflects outer segments (472-708/hr) vs core (1,600-2,400/hr). Trucking + I-19 merge. |
| Major arterials (Speedway, Broadway, Grant, Oracle, etc.) | 1,500-3,000 | Spread across dozens of corridors; rideshare surge around 2 AM bar close |
| Collectors + local streets | 2,000-4,000 | Bar/restaurant close-out, shift workers (hospitals, hotels, warehouses), convenience runs |
Who is on the road at this hour
- Bar/restaurant close-out — AZ bars serve until 2 AM; regulatory fact (ARS 4-244) that shapes the late-night traffic curve
- Rideshare + taxi drivers — Surge pricing window around bar close; concentrated near entertainment districts
- Shift workers — Hospitals, hotels, warehouses, distribution centers; predictable patterns
- Long-haul truckers — Interstate corridors operate 24/7 regardless of day of week
- Late-night errands — Convenience store runs, fast food, pharmacy; scattered and unpredictable
- Unaccounted movement — People who are simply driving with no categorizable destination
Corridor-specific: Catalina Foothills area
Applied to the Nancy Guthrie case geography. Starting point: 5820 N Camino Escalante, Tucson AZ (Catalina Foothills). The map tool calculates drive-time radii, camera coverage, and escape route scenarios from this location.
Swan Rd south to I-10
Direction: South
To I-10: ~7 mi / 12 min
Camera density: Low
Mostly residential; minimal surveillance until I-10 ramps
Residential feeder; minimal surveillance; connects to I-10 at Palo Verde/Country Club. Straight south, mostly 45 mph, few signals at night. At 1-3 AM Sunday: expect <50 vehicles on this entire corridor. I-10 at Country Club (Exit 267) carries 624-936 vehicles/hr at this hour (ADOT AADT-derived).
Campbell Ave south to I-10
Direction: South-Southwest
To I-10: ~7 mi / 14 min
Camera density: Low-moderate
Residential transitioning to commercial near Grant/Speedway
Residential to commercial transition; hits I-10 at Congress/Speedway area (Exit 258). More witness potential at arterial intersections (Grant, Speedway, Broadway). I-10 at Congress (Exit 258) carries 1,600-2,400 vehicles/hr at this hour — highest segment in corridor (ADOT AADT-derived).
Sunrise Dr west to Oracle Rd (SR-77)
Direction: Northwest
To I-10: ~7 mi / 12 min
Camera density: Low
Suburban residential; Oracle Rd has scattered commercial cameras
Connects to Oracle (SR-77) north toward Oro Valley; or south to I-10 at Ina/Orange Grove area. ADOT cameras at I-10 interchanges (Cortaro, Ina, Orange Grove). I-10 at Cortaro (Exit 246) carries 1,048-1,572 vehicles/hr (ADOT AADT-derived).
Kolb Rd south to I-10 east
Direction: Southeast
To I-10: ~8 mi / 13 min
Camera density: Low-moderate
Long residential stretch; thins out toward Vail
Long residential stretch; connects to I-10 east toward Houghton/Vail. Past Houghton Rd interchange, camera gaps widen to 5+ miles. Lowest post-metro surveillance of any I-10 direction. I-10 east past Houghton (Exit 275) carries 472-708 vehicles/hr — lowest in corridor (ADOT AADT-derived).
Tanque Verde Rd / Catalina Hwy northeast
Direction: Northeast
To I-10: N/A — away
Camera density: Very low
Dead-ends into Coronado NF / Mt. Lemmon; no through-traffic
Dead-ends into Coronado NF/Mt. Lemmon; no through-traffic at 1-3 AM. Not a viable egress route for leaving the metro. Relevant only if a destination, not a transit corridor.
All corridor distances, travel times, and camera density assessments are estimated. Camera data combines ADOT highway cameras (verified positions) and OSM community-mapped cameras (variable completeness). Private cameras not included.
I-10 corridor — ADOT camera coverage
The map tool catalogs ADOT highway cameras along I-10 from Cortaro Rd (Exit 246) through Houghton Rd (Exit 275). Camera spacing averages approximately 1-2 miles through the urban core but thins significantly past the Valencia Rd interchange heading southeast and past Cortaro/Ruthrauff heading northwest. The WB I-10 escape corridor analysis in the map tool identifies this thinning as a surveillance vulnerability — once past Marana, camera gaps widen to 5+ miles.
Urban core (Speedway to Ina)
1-2 mi gaps
~16 ADOT cameras
Transition zone
3-5 mi gaps
~6 ADOT cameras
Open desert
5+ mi gaps
Sporadic
I-10 Tucson: Segment-by-Segment AADT SOURCED
ADOT 2021 AADT (pre-construction baseline). Sunday 1 AM estimates derived using FHWA hourly factor (0.8-1.2% of AADT). Segments run NW to SE.
| Segment | AADT | K% | T% | Sun 1AM Low | Sun 1AM Mid | Sun 1AM High |
|---|
| Exit 246 Cortaro to 248 Ina | 131,000 | 8 | 9 | 1,048 | 1,310 | 1,572 |
| Exit 248 Ina to 250 Orange Grove | 143,000 | 8 | 9 | 1,144 | 1,430 | 1,716 |
| Exit 250 Orange Grove to 252 Ruthrauff | 148,000 | 8 | 9 | 1,184 | 1,480 | 1,776 |
| Exit 252 Ruthrauff to 254 Prince | 155,000 | 7 | 8 | 1,240 | 1,550 | 1,860 |
| Exit 254 Prince to 255 Grant | 168,000 | 7 | 8 | 1,344 | 1,680 | 2,016 |
| Exit 255 Grant to 257 Speedway | 184,000 | 5 | 9 | 1,472 | 1,840 | 2,208 |
| Exit 257 Speedway to 258 Congress | 187,000 | 7 | 10 | 1,496 | 1,870 | 2,244 |
| Exit 258 Congress to 259 22nd St | 200,000 | 8 | 9 | 1,600 | 2,000 | 2,400 |
| Exit 259 22nd St to 260 I-19 Jct | 176,000 | 8 | 8 | 1,408 | 1,760 | 2,112 |
| Exit 260 I-19 Jct to 261 6th Ave | 155,000 | 8 | 8 | 1,240 | 1,550 | 1,860 |
| Exit 261 6th Ave to 262 Kino | 137,000 | 8 | 7 | 1,096 | 1,370 | 1,644 |
| Exit 262 Kino to 264 Alvernon | 119,000 | 8 | 8 | 952 | 1,190 | 1,428 |
| Exit 264 Alvernon to 265 Palo Verde | 103,000 | 8 | 9 | 824 | 1,030 | 1,236 |
| Exit 265 Palo Verde to 267 Country Club | 89,000 | 8 | 10 | 712 | 890 | 1,068 |
| Exit 267 Country Club to 268 Kolb | 78,000 | 8 | 11 | 624 | 780 | 936 |
| Exit 268 Kolb to 270 Wilmot | 71,000 | 8 | 12 | 568 | 710 | 852 |
| Exit 270 Wilmot to 275 Houghton | 59,000 | 9 | 14 | 472 | 590 | 708 |
| TOTAL I-10 TUCSON CORRIDOR | — | — | — | 18,424 | 23,030 | 27,636 |
Per-segment, per-hour estimates. Vehicles appear on multiple segments during a trip — corridor total represents segment-level exposure, not unique vehicles.
Case-relevant corridors: ADOT-anchored estimates DERIVED
| Route from residence | I-10 Seg AADT | Sun 1AM Low | Sun 1AM High | Notes |
|---|
| Swan Rd → I-10 (Exit 267) | 78,000 | 624 | 936 | Residential feeder. Minimal surveillance until I-10 ramps. |
| Campbell Ave → I-10 (Exit 258) | 200,000 | 1,600 | 2,400 | Highest-volume segment. Commercial intersections add witnesses. |
| Kolb Rd → I-10 East (Exit 268) | 78,000 | 624 | 936 | Long residential stretch. Past Houghton, camera gaps widen to 5+ mi. |
| Oracle → I-10 NW (Exit 246) | 131,000 | 1,048 | 1,572 | ADOT cameras at Cortaro, Ina, Orange Grove interchanges. |
What this means for the investigation
<50
Estimated vehicles on any single residential feeder road at 1-3 AM Sunday. The total number of potential witness vehicles on any single corridor at that hour is likely in the low hundreds at most.
12-14
Minutes from residence to I-10 access via any corridor. Once on I-10, a vehicle has directional options: NW toward Marana/Phoenix, SE toward Vail/Benson, or south via I-19 toward Nogales.
3
Targeted data sources that would matter most: ALPR (automated license plate reader) logs at key intersections, gas station / convenience store cameras along corridors, and cell tower connection records for the 1-3 AM window.
Law enforcement reviewing this window faces a needle-in-haystack problem: enough vehicles on the road that movement would not be conspicuous, but few enough that identifying a specific vehicle requires targeted data sources (ALPR, gas station cameras, cell tower records) rather than volume-based pattern matching.
Data confidence summary
| Data point | Previous | Now | Source |
|---|
| I-10 AADT per segment | ESTIMATED | SOURCED | ADOT 2021 Interstate AADT Publication |
| Sunday 1 AM hourly factor (0.8-1.2%) | ESTIMATED | SOURCED | FHWA Traffic Monitoring Guide, HCM |
| I-10 per-segment Sunday 1 AM count | ESTIMATED | DERIVED | ADOT AADT × FHWA factor (bounded range) |
| K Factor (design hour %) | — | SOURCED | ADOT 2021 publication per segment |
| Metro population + registered vehicles | SOURCED | SOURCED | Census/ACS, ADOT registrations |
| Sunday 1-3 AM = weekly low | SOURCED | SOURCED | FHWA, state DOT continuous count stations |
| AZ bar closing time (2 AM) | SOURCED | SOURCED | ARS 4-244 regulatory fact |
| Arterial feeder road counts | ESTIMATED | ESTIMATED | Still pattern reasoning; needs PAG data |
| <50 vehicles per residential corridor | ESTIMATED | PLAUSIBLE | Consistent with I-10 anchor data but unverified |
| Camera density assessments | ESTIMATED | ESTIMATED | ADOT verified + OSM; private not included |
Cross-reference: sources for harder numbers
- Pima County + City of Tucson permanent traffic count stations — Hourly volumes available through ADOT Traffic Data portal. Would replace estimated instantaneous count with observed data.
- TPD/PCSD calls for service and traffic stop logs — Calls for service, traffic stops, DUI enforcement activity during 1-3 AM window. Indirect but concrete proxy for vehicles officers are encountering.
- ADOT traffic count maps (corridor-specific) — Some stations report hourly-level data for individual corridors. Could validate or replace the road-type breakdown.
- Pima Association of Governments (PAG) regional traffic model — May have time-of-day VMT distributions specific to Tucson metro rather than relying on national factors.
- ALPR data (if accessible via FOIA) — Automated License Plate Reader logs from TPD or PCSD would give actual vehicle counts at specific locations during this window.
Data request list: sources for hourly-level verification
The ADOT AADT + FHWA factors approach replaces national guesswork with published data, but raw hourly counts from local sources would be definitive.
- ADOT TDMS Hourly ATR Data — Hourly volume from Automatic Traffic Recorder stations on I-10 (Exits 246-275), Sunday 0100-0300. Available at adot.ms2soft.com. Public, no login. Would replace the 0.8-1.2% FHWA factor with observed Sunday 1 AM counts. HIGHEST VALUE
- PAG Regional Traffic Count Data — Hourly counts for Swan Rd, Campbell Ave, Oracle Rd, Kolb Rd, Sunrise Dr, Tanque Verde Rd. Via pagregion.com. Contact: PAG, (520) 792-1093. Would validate the <50 vehicles per corridor estimate.
- PAG Regional Traffic Model (Time-of-Day Factors) — Tucson-specific time-of-day VMT distribution factors from 2021 Traffic Count Improvement Project or 2023 Traffic Performance Measure Project. Would replace national FHWA factors with local data.
- TPD/PCSD Calls for Service (FOIA) — Aggregate calls for service, traffic stops, DUI enforcement during Sunday 0100-0300 for East Division / Catalina Foothills. Available via FOIA to TPD and PCSD. Indirect but concrete proxy for traffic volume.
- ALPR Data (FOIA — long shot) — Automated License Plate Reader scan counts (not plate data) at key intersections, aggregated by hour. Definitive vehicle count if obtainable. Likely denied or heavily redacted.