Traffic collision Study Guide

📖 Core Concepts Traffic collision – Any contact between a vehicle and another vehicle, person, animal, object, or stationary obstruction. Major collision types – Head‑on, rear‑end, side‑impact, rollover, road‑departure. Human‑factor dominance – ≈ 93 % of crashes involve driver error, intoxication, or distraction. Speed & injury risk – Crash risk rises when traveling slower or faster than the traffic median; injury risk climbs exponentially at speeds far above the median. Seat‑belt effectiveness – Proper use cuts death risk by 45 %. Collision migration – Safety improvements at one site can shift crashes to adjacent locations if driver behavior changes (risk compensation). Rate metrics – Crash rates = (number of crashes/deaths/injuries) ÷ (exposure: population, vehicles, drivers, or vehicle‑kilometres travelled). Choice of denominator depends on the safety question. 📌 Must Remember Driver error accounts for ≈ 93 % of all crashes (U.S./U.K. data). Seat‑belt use → 45 % reduction in fatality risk. Texting while driving raises crash risk 23‑fold; dialing 12‑fold; reading/writing 10‑fold. Speeding contributed to 26 % of U.S. traffic deaths (2018). Roundabouts cut overall crashes 38 % and serious/fatal crashes 90 %. Automated speed enforcement lowers injury‑causing crashes 20‑25 %. Global 2013 impact – 54 million injuries, 1.4 million deaths (≈ 2.5 % of all deaths). Africa highest death rate: 24.1/100 000; Europe lowest: 10.3/100 000. Teen graduated licensing → measurable drop in teen fatal crashes. 🔄 Key Processes Collision Risk from Speed Identify average traffic speed → compare vehicle speed → if Δspeed > 0 (fast) or < 0 (slow) → risk ↑; injury severity ↑ exponentially with high Δspeed. Collision Migration Cycle Implement safety measure at site → local crash count ↓ → drivers perceive road as “safer” → risk‑taking ↑ on adjacent segments → crashes ↑ there → net effect may be neutral. Emergency Response Impact Crash occurs → sensor or cell‑phone alerts → EMS dispatched → shorter response time + proximity to trauma center → mortality ↓. 🔍 Key Comparisons Head‑on vs. Rear‑end – Head‑on → highest fatality risk (opposing forces); Rear‑end → generally lower severity but common. Seat‑belt vs. No seat‑belt – 45 % lower death risk vs. significantly higher ejection/serious injury risk. Texting vs. Dialing while driving – 23‑fold vs. 12‑fold crash risk increase. Speeding vs. Normal speed – Same crash probability increase, but injury severity escalates exponentially. Human error vs. Vehicle design – Human error ≈ 93 % of crashes; vehicle safety features mitigate injury severity, not crash occurrence. ⚠️ Common Misunderstandings “Speeding is the only cause of fatal crashes.” – Speed is a major factor (26 %) but interacts with impairment, distraction, and road design. “Seat belts eliminate crash risk.” – They reduce fatality risk, not the likelihood of a crash. “Roundabouts always reduce crashes everywhere.” – Benefits are strongest where conflict points are high; poorly designed roundabouts can increase minor crashes. “All countries count fatalities the same way.” – Definitions vary (e.g., U.S. = death within 30 days; France pre‑2005 = 6 days). 🧠 Mental Models / Intuition Exponential injury model – Think of crash severity as a curve that stays flat near median speed then shoots up sharply as speed climbs. 23‑fold texting rule – Treat every text as a “virtual” 23 extra drivers on the road. Risk compensation – Adding a safety feature often leads drivers to “drive freer,” partially offsetting the benefit. 🚩 Exceptions & Edge Cases Road‑departure crashes – Even with perfect driver behavior, poor roadway design (e.g., lack of guardrails) can cause serious incidents. Fatality definition variance – A death at 28 days counts in U.S. FARS but would be excluded in a 7‑day definition system. Collision migration – Safety upgrades may not reduce total crashes if adjacent segments see a rise. Low‑speed crashes – Still cause injuries when vehicle mass is high (e.g., large SUVs). 📍 When to Use Which Roundabout vs. Signalized intersection – Choose roundabouts where traffic volumes are moderate‑high and severe‑crash history is high; signals where pedestrian flow is dominant. Speed cameras vs. police patrol – Deploy automated enforcement on long, straight stretches with documented speed variance; use patrols in high‑conflict zones (schools, work zones). Graduated licensing vs. blanket age restrictions – Apply GDL for novice drivers (16‑20) to cut teen fatalities; use universal restrictions only when data show age‑related risk spikes. Seat‑belt campaigns vs. technology incentives – Emphasize seat‑belt messaging in populations with low compliance; promote advanced driver‑assist systems where fleet turnover is rapid. 👀 Patterns to Recognize High injury/death rates + low‑income country – Expect older vehicle fleets and poorer road infrastructure. Speed‑related crash questions – Look for “exponential” wording → answer relates to severity, not just probability. Human factor + impairment – If a scenario mentions alcohol or cannabis, consider combined effect (greater than additive). Collision migration clue – Any mention of “adjacent road segment” or “risk compensation” signals the need to account for displaced crashes. 🗂️ Exam Traps Distractor: “Texting is only 2‑fold riskier than normal driving.” – Incorrect; the outline states a 23‑fold increase. Distractor: “Seat‑belt use eliminates all serious injuries.” – Wrong; it reduces death risk by 45 % but does not prevent all severe injuries. Distractor: “All crashes are caused by driver error.” – Nearly true (≈ 93 %) but vehicle design, road environment, and speed also play roles. Distractor: “Roundabouts always lower total crashes by 90 %.” – The 90 % figure applies only to serious‑injury/fatal crashes, not all crashes. Distractor: “Speed cameras cut all crashes by 50 %.” – The data show a 20‑25 % reduction in injury‑causing crashes, not a universal 50 % cut.