# Presentation: 014196

## Light Vehicle Rollover

- Background on NHTSA’s Activities in this Area

## Light Vehicle Tow-away Crashes 1995-1999 NASS-CDS3.4 million  crashes per year

- Light Vehicle Tow-away Crashes 1995-1999 NASS-CDS3.4 million  crashes per year

- Light Vehicle Occupant Fatalities 1999 FARS31,921 total occupants killed

## Occupant Fatalities 1999 FARS

- Occupant Fatalities 1999 FARS

- Cars

- LTVs

## Occupant Fatalities 1999 FARS

- Cars

- SUVs

- Vans

- Pickups

## Chronology of NHTSA Rollover Actions - Page 1

**1973**: Advance Notice of Proposed Rulemaking on Minimum Standard for Rollover Resistance
**1978: **Terminate action because of the difficulty in getting tip-up and lack of repeatability
**1986:** Rep. Wirth petitions for minimum standard based on Static Stability Factor (SSF)
**1987:** NHTSA denies Wirth petition because of difficulties measuring SSF and because SSF, while correlated to rollover risk if there is a crash, does not predict likelihood of crash
**1992**: NHTSA issues ANPRM for minimum standard for rollover resistance based on vehicle metrics

## The First NHTSA Rollover Rulemaking Action

- 1973 ANPRM for safety standard “that would specify minimum performance requirements for rollover resistance”
- Focus was on safety standard for the next 20 years
- Goal is to set a level that eliminates unreasonable risk to safety
- Challenge is to make it meaningful for cars and light trucks

## The First NHTSA Rollover Rulemaking Action (Cont’d)

- Agency’s early-70’s work was focused on rollovers on flat road surfaces, with hard driving maneuvers to induce rollover
- After years of work, we concluded
- Difficult to get wheel lift with even these maneuvers
- Even more difficult to repeat wheel lift response
- Could not use these maneuvers for standard

## The Second NHTSA Rollover Rulemaking Action

- NHTSA’s early work was with dynamic tests, but found too much variability
- Mr. Wirth asked agency to use vehicle physical characteristics (SSF) as a surrogate measure of rollover propensity
- From mid-80’s to mid-90’s, NHTSA analyzed different vehicle metrics as a potential means to address rollover
- Three widely accepted metrics

## Static Stability Factor (SSF)T/2hFirst order estimate of steady state lateral acceleration when rollover begins.

## Critical Sliding Velocity (CSV) Theoretical lowest speed at which sliding sideways into a curb causes rollover.

- Vehicle Motion

## Tilt Table Angle (TTA) Minimum table angle at which a vehicle on the table will tip over.

## The Second NHTSA Rollover Rulemaking Action (Cont’d)

- After evaluating a standard requiring a minimum SSF, NHTSA concluded:
- Requested minimum would essentially make all vehicles cars - NOT NHTSA’s mission
- SSF was too simple -correlated to rollover given a crash, but could not predict likelihood of being in a crash
-  Difficult to repeatably measure center-of-gravity height

## The Third NHTSA Rollover Rulemaking Action

- In 1992, NHTSA began a rulemaking with the goal of using a vehicle metric other than SSF to establish a minimum performance standard
- Hoped this would:
- Establish a base level of rollover resistance
- Use greater ease and repeatability of metrics
- Find a metric better than SSF

## Chronology of NHTSA Rollover Actions - Page 2

**1994:** NHTSA terminates rulemaking on minimum standard, but proposes consumer information based on vehicle metric
**1994:** Congress suspends rollover rulemaking until National Academy of Sciences (NAS) study of consumer information
**1996:** NAS study published
**1996:** NHTSA begins new study of feasibility of dynamic rollover
**1999: **NHTSA publishes report of its testing results

## Safety Standard vs. Consumer Information

- In 1994, we terminated rulemaking on a vehicle standard - benefits were too low to justify costs of redesigning most light trucks
- Because of the difficulties of the standard, NHTSA suggested providing consumer information, instead of a standard
- This would give the public helpful information about what they are buying without restricting their ability to buy small SUVs and pickups

## Recent NHTSA Testing of Dynamic Maneuvers

- In 1997, NHTSA set out to see if it was now possible to develop a practicable, repeatable and appropriate emergency handling test
- Chose best procedures from existing literature and selected some for further analysis
- After analysis, did further testing with three maneuvers

## J-Turn Maneuver

- start

- steering  pulse

- brake pulse  (if applicable)

- hold steering & throttle

- accelerate to target  test speed

## Toyota Fishhook Maneuver

## Resonant Steer Maneuver

- increasing steering frequency

- Start: 0.2 Hz

- End: 1.5 Hz

- Vehicle Path

- _Step 1_  Measure resonant steering frequency:

- Start: 0.2 Hz

- End: 1.5 Hz

- Vehicle Path

- _Step 2_  Drive test vehicle at resonant steering frequency:

- Vehicle Path

- constant steering frequency

## Conclusions on Dynamic Testing vs Metrics

- These dynamic tests give reasonable results that correspond to real-world performance
- _But_ dynamic tests are not better than metrics at predicting rollover involvement.
- Extra expense of dynamic testing is substantial.
- Several practical problems remain with vehicle testing:
- Use of human driver leads to safety concerns and mandates use of outriggers.
- Outriggers affect handling.
- Tire debeading may mask true limit behavior

## Why Choose SSF as the Metric for Consumer Information?

- None of the three metrics was the clear winner statistically.
- SSF is the only metric that will do no harm.
- SSF has broad industry acceptance as “first order” design consideration.
- SSF is least complex, intuitively related to rollover.

## Rollover Actions in the Past 12 Months

**June 2000:**  NHTSA proposes rollover consumer information using SSF
**October 2000:** Congress mandates NAS study of NHTSA’s proposed SSF rollover information program
**November 2000:** Congress requires NHTSA to provide consumer information on performance in dynamic rollover testing as of November 2002
**January 2001:** NHTSA issues first rollover ratings based on SSF** **