IIHS

Articles, guides, and products tagged "IIHS" — a combined view of every catalogue resource on this topic.

User guide

Defensive riding in mixed motor traffic: lane positioning, primary vs secondary position, door zone, right hook + left cross at the intersection, SMIDSY / look-but-failed-to-see — how to avoid conflicts with cars

Unlike braking technique, cornering, or night riding, a separate safety layer is the **strategy of interacting with motor traffic**: where to position yourself in the lane, how to read drivers before an intersection, where the door zone sits, what right hook and left cross are, and why statistically the **intersection** — not the straight section — is the more dangerous segment (NACTO: >40% of urban bike fatalities in 2022 happened at intersections; UK DfT 2022: e-scooter casualty rate is three times higher than for pedal cycles). This guide transfers to the e-scooter the classic principles of vehicular cycling (John Forester, *Effective Cycling* 1976, MIT Press 7th ed. 2012), Smart Cycling of the League of American Bicyclists, the NACTO Urban Bikeway Design Guide 3rd ed. 2025, the AASHTO Guide for the Development of Bicycle Facilities, ROSPA UK road-safety guidance, IIHS, and AAA Foundation research. Covers: lane-positioning theory (primary vs secondary position; why 'as far right as possible' is the worst strategy); door zone (12-27% of urban bike collisions — Wikipedia; Dutch Reach countermeasure); right hook (a turning vehicle crosses the bike lane), left cross (an oncoming driver turns across your path); SMIDSY / look-but-failed-to-see as a perceptual phenomenon (Hurt Report 1981 motorcycle baseline, 75% of motorcycle crashes involve a passenger car, 66% are ROW violations); 5 active-signalling rules (positioning + eye-contact + speed-modulation + escape-path + worst-case escape); why a bike lane is not always safer than the road; how to ride with the flow (vehicular) vs in a facility (segregated); a 30-minute practice drill.

13 min read

User guide

Speed wobble and weave instability on e-scooters: two eigenmodes of two-wheeled vehicle dynamics, eigenvalue analysis of the 4-DOF linearized model (Whipple → Sharp → Meijaard 2007 Proc. R. Soc. A), why 8-10-inch wheels and a high h/L mass-center ratio produce 6-10 Hz wobble at 35-45 km/h, three damping mechanisms (tire side-slip + headset preload + steering damper), diagnostics and rider recovery protocol

Stability at speed is not a question of grip strength but a question of the eigenmode spectrum. A two-wheeled vehicle (bicycle, motorcycle, e-scooter) under forward motion has a linearized 4-DOF model from Whipple (1899) → Sharp (1971) → Meijaard, Papadopoulos, Ruina, Schwab (2007) Proc. R. Soc. A 463:1955-1982 whose eigenvalues yield **two oscillatory modes**: weave (2-4 Hz, lateral inverted-pendulum oscillation of the entire frame with steering in phase) and wobble (6-10 Hz, pure steering-only oscillation with the frame nearly stationary). Depending on forward speed `v`, the real part of one or both eigenmodes passes through zero — a bifurcation where the mode flips from damped to undamped, and any small disturbance (road irregularity, gust crosswind, rider input) excites self-sustained oscillation. Why e-scooter parameters (wheel radius R≈100 mm vs motorcycle 300 mm → 9× lower gyroscopic stabilization; h/L≈0.55 vs 0.35 → higher mass-center normalized to wheelbase → lower critical speed; m_rider/m_vehicle≈4-6 vs ~1 → rider dominates dynamics; headset preload often poorly maintained) shift wobble frequency into the 6-10 Hz range, where rider neuromuscular reflex (80-150 ms latency per Sharp 1971 and Cossalter 'Motorcycle Dynamics' 2nd ed. 2006) cannot stabilize phase and often makes wobble worse through positive-feedback transfer function. Three damping mechanisms — tire side-slip relaxation (Pacejka 'Tire and Vehicle Dynamics' 3rd ed. 2012), headset bearing rotational friction (preload-dependent, ISO 12240 angular contact specs), and external steering damper (hydraulic as in MX/motorcycles, OEM on Dualtron X2 + Wolf King). Diagnostic weekly 3-point play-check (headset move-test, fork twist-test, wheel-bearing rock-test). Rider recovery protocol at speed is counterintuitive and opposite to instinct: **do not grip tight (gripping tighter couples rider-as-amplifier into transfer function and worsens wobble — Sharp 1971); relax hands gently, shift weight rearward onto heels on the rear third of the deck (reduces front-wheel load and thus trail-dependent wobble torque), clamp the stem with knees (couples rider mass to frame, raises effective damping ratio), apply rear brake only (front brake at speed worsens wobble through geometric + gyroscopic coupling per Cossalter 2006 §8.6), and ease speed down to ~20 km/h where the mode naturally decays**. Manufacturer responses: Bird One geometry update 2019 (more conservative head angle after reports of high-speed wobble per IIHS micromobility data); Lime Gen 4 longer wheelbase; hyperscooter class (Dualtron X2, Wolf King GT Pro) ship with hydraulic steering dampers as standard. ENG-first sources: Meijaard et al. 2007 Proc. R. Soc. A 463:1955-1982 DOI 10.1098/rspa.2007.1857; Sharp 1971 JMES 13(5):316-329; Cossalter 'Motorcycle Dynamics' 2nd ed. 2006; Schwab & Meijaard 2013 Vehicle System Dynamics 51(7):1059-1090; TU Delft Bicycle Lab; Pacejka 'Tire and Vehicle Dynamics' 3rd ed. 2012; NHTSA HS-810-844; IIHS Status Report 2022.

13 min read

User guide

Emergency maneuvers and obstacle avoidance on an e-scooter: swerving, threshold braking, two-step weight transfer, target fixation, and PIEV reaction time

Emergency maneuvering is a discipline distinct from planned braking and from steady-state cornering. There is no time for a second attempt — there is one decision made in 0.5–1.5 seconds and one motor sequence executed in the next 0.3–0.8 seconds. If the decision is wrong (you brake when you should have swerved, or you swerve when you should have stopped), two-wheeled physics with small wheels and a high center of gravity punishes you immediately: 86 million shared trips on e-scooters in 2019 ([NACTO — Shared Micromobility in 2019](https://nacto.org/wp-content/uploads/2020/08/2019sharedmicromobilityreport_final.pdf)) generate 118,485 ED visits in 2024 ([CPSC — E-Scooter and E-Bike Injuries Soar, 2024](https://www.cpsc.gov/Newsroom/News-Releases/2024/E-Scooter-and-E-Bike-Injuries-Soar-2022-Injuries-Increased-Nearly-21)), and CPSC explicitly notes that e-scooters have much higher centers of gravity and smaller wheels with less shock absorption, so pavement quality matters significantly more than it does for bikes or e-bikes. Small wheels and a tall CoG mean that the same patch of damaged pavement that a cyclist will absorb as a transient ride-quality blip will throw an e-scooter rider over the handlebars. This guide covers the two symmetric skills the Motorcycle Safety Foundation (MSF) calls core emergency skills: **threshold braking** (maximum deceleration at the edge of wheel lockup) and **emergency swerve** (rapid line change without braking during the lean phase). Plus — when to use which, and when to combine them sequentially. ENG-first sources: MSF Basic RiderCourse / 'Do I Brake or Swerve' / Quick Video Tips, Wikipedia (Countersteering, Threshold braking, Dooring), CyclingSavvy (Emergency Maneuvers, Door Zone Tragedy), Cycle World and MCrider (target fixation), AASHTO (2.5 s PIEV), CPSC injury reports, IIHS sidewalk speed studies, Nature Communications (projected time-to-collision e-scooter), ScienceDirect (e-scooter vs bicycle crash typology), 99% Invisible (Dutch Reach), Bennetts (brake and swerve), Hupy and URide (emergency drill protocols).

14 min read