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Vehicle Design and the Physics of Traffic Safety

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Vehicle Design and the Physics of Traffic Safety Powered By Docstoc
					Vehicle Design and the
Physics of Traffic Safety


    Professor Marc Ross
    University of Michigan
Last Week’s Talk: Weight reduction
increases Fuel Economy
1.       Smaller vehicles, as done in the late 1970s
2.       Change basic structure, e.g. unibody (instead of today’s
         body-on-frame SUVs - also called car-based & crossover)
3.       Lighter materials
     –     ultra-high strength steels, aluminum
     –     composites, sandwich structures
4.       Reduce Engine Size
     –     Smaller engine capable of switching to high power
           •   high speed engine, or
           •   turbocharge, or
           •   variable displacement, split engine
5.       Smaller automatic transmission
     –     automatic "manual" or double clutch or CVT
6.       Rationalization of Vehicle Parts
                                                                     Weight, Displacement & Fuel Reduction
                                                                        (late 1970s Oil Shortages & CAFÉ Legislation)
                                                                                   new cars, sales weighted
                                       7.0

                                                                                  37% fuel intensity reduction, 1975-1981
                                                                                  or 60% fuel economy increase
  Weight Displacement Fuel Intensity
                       (gal/100 mi)




                                       6.0

                                                                                  24% weight reduction, 1976-1980
                                       5.0

                                                                                  35% displacement reduction, 1976-1980
            (liters)




                                       4.0
(1000 lbs)




                                       3.0




                                       2.0

                                                                                                          How was this accomplished?
                                       1.0
                                                                                                  Fuel Intensity - gal/100 mi
                                                                                                  Inertial Weight - lbs
                                       0.0
                                                                                                  Engine Displacement - liters
                                         1975               1980           1985                1990               1995           2000   2005

                                                EPA: Light-Duty Automotive Technology & Fuel Economy Trends: 1975 Through 2004
Cars mass in 1970s now called SUVs
               Cars: Percent Fraction of Sales by EPA Weight Class (lbs)                                       …….
30


                                                                      2001
25

               1986

20




15


                                                                                                              1976
10




 5




 0
 2000               2500                3000                3500                 4000          4500    5000      5500   6000
     Source: Heavenrich & Hellman "fuel economy trends" http://www.epa.gov/otaq/fetrends.htm          ………..
How does the mass effect
    societal safety?


    Note: it does not if the
   vehicle is designed well
                                    Demo 1: Car Track

                Mass War
• It has been argued that it is much safer to
  ride in a heavy vehicle.
• Auto manufacturers have responded by
  offering very heavy SUVs (Hummer,
  Excursion, Durango, etc.).
• Truth: Camry, has a risk for its own driver
  similar to that for a midsize and large
  SUVs; but the corresponding risk when a
  Camry collides with another vehicle is
  much lower.
Crash A: Frontal



                             Intact effects      1. At the same speed a
                                                    frontal crash is less
                                                    injurious.
                                                 2. If speed is not very
                                                    high, then there is no
                                                    intrusion in a frontal
                                                    crash. Restraints
                       High Energy Absorption       can protect
                                                    occupants.
Crash B: Side-Impact                             3. In a side-impact
                                                    crash, sedan
                                                    occupants are at risk
                                                    from hard-contact.
                             Intrusion effects   4. In both, the SUV
                                                    occupants are
                                                    slightly less at risk
                                                    except for rollover.



Demo 2: Egg              Low Energy Absorption
Crash Test #5161 Video
             Crash Test #5161 Video
  Near-side Forces (G’s) vs. Time (ms)   Far-side Forces (G’s) vs. Time (ms)


                       Δp = ΔF * Δt                             Δp = Δf * ΔT




• Pelvic forces (acceleration in G’s) much stronger than
center-of-mass acceleration of target vehicle
• Momentum conserved (Δp)
• Pelvis: Big Δforce & small Δtime
• Vehicle: Small Δforce & big Δtime
                                      Demo 3



        Force Transfer

                         1. Same impulse
                         2. Left-side (near-side):
                            serious injuries
                         3. Far side: injuries usually
                            less serious and fewer
                         4. Passenger experiences
                            ~¼ the magnitude of the
fT Ft                       force the driver
                            experiences.
Risk: Deaths/million registered Vehicles
             of given type       4 to 5 times
                                  More Risk




                             2 to 3 times
                              More Risk
                                                        Risks: Driver Deaths/Year per Million Vehicles
                                                  175                                   (most-popular models 1997-2001)
Risk to drivers of other vehicle by named model




                                                  150       Subcompact cars
                                                            Compact cars
                                                            Midsize cars                                       Ram 1500
                                                            Large cars
                                                  125
                                                            Minivans
             in all 2-vehicle crashes




                                                                                           Dakota
                                                            Pickup trucks
                                                                                                                            F-150
                                                            SUVs
                                                  100       Sports cars                                  Marquis, Malibu,
                                                                                                                                    Chevy/GMC
                                                                                                                                    C/K 1500
                                                                                                          Taurus/Sable,
                                                                                                           Grand Prix
                                                                                          Tahoe
                                                                                                                                    Ranger
                                                   75
                                                                   Chevy Suburban
                                                                                                               Explorer      Tacoma
                                                                                         Astro Van
                                                                           Expedition          Cherokee       TownCar,                                    S-10
                                                                                                                       Wrangler Blazer
                                                        Caravan, Windstar,                                    Lumina
                                                   50                                   Altima Intrepid                                Mustang
                                                                                                        4Runner
                                                           Town & Country    G Cherokee
                                                                                                                                Grand Am             Neons
                                                                               Venture Deville                      Stratus                Cavalier/
                                                                                                             Sentra              Escort/                         Corvette
                                                                                                                                           Sunfire
                                                                              Camry        626                  LeSabre, Corolla Tracer
                                                   25         CR-V
                                                                       Avalon               Legacy
                                                                                  Jetta                Civic Saturn
                                                                                     Accord,
                                                                                     Maxima         Century
                                                    0
                                                        0           25             50               75           100                125         150        175        200
                                                                             Risk to drivers in vehicle by named model in all crashes
                                                        Risks: Driver Deaths/Year per Million Vehicles
                                                  175                                   (most-popular models 1997-2001)


                                                                                                • Corvette demonstrates both the role of driver
Risk to drivers of other vehicle by named model




                                                            Subcompact cars
                                                  150                                           behavior and vehicle design. Corvette is
                                                            Compact cars
                                                            Midsize cars
                                                                                                dangerous to its own driver. The driver is very
                                                                                                           Ram 1500
                                                            Large cars                          aggressive as shown by violations record.
                                                  125                                           • In spite of aggressive driving, the Corvette is
                                                            Minivans
             in all 2-vehicle crashes




                                                            Pickup trucks                 Dakota
                                                                                                                      for
                                                                                                relatively safe F-150drivers of other vehicles with
                                                            SUVs                                which it crashes. Chevy/GMC
                                                  100       Sports cars                                                   safest
                                                                                                • Jetta is one of the C/K 1500 cars in spite of
                                                                                                     Marquis, Malibu,
                                                                                                      Taurus/Sable,
                                                                                          Tahoe
                                                                                                aggressive drivers as shown by violations
                                                                                                       Grand Prix
                                                                                                                          Ranger
                                                   75                                           record.
                                                                   Chevy Suburban
                                                                                                              Explorer   Tacoma
                                                                                        Astro Van
                                                                           Expedition         Cherokee       TownCar,                                    S-10
                                                                                                                      Wrangler Blazer
                                                        Caravan, Windstar,                                   Lumina
                                                   50                                  Altima Intrepid                                Mustang
                                                                                                       4Runner
                                                           Town & Country    G Cherokee
                                                                                                                               Grand Am             Neons
                                                                               Venture Deville                     Stratus                Cavalier/
                                                                                                            Sentra              Escort/                         Corvette
                                                                                                                                          Sunfire
                                                                              Camry       626                  LeSabre, Corolla Tracer
                                                   25         CR-V
                                                                       Avalon              Legacy
                                                                                 Jetta                Civic Saturn
                                                                                    Accord,
                                                                                    Maxima          Century
                                                    0
                                                        0           25             50            75             100          125            150           175        200
                                                                             Risk to drivers in vehicle by named model in all crashes
                                                        Risks: Driver Deaths/Year per Million Vehicles
                                                  175                                   (most-popular models 1997-2001)

                                                                                                 • Here we are considering sub-compact cars.
Risk to drivers of other vehicle by named model




                                                            Subcompact cars
                                                  150                                            They have about the same mass.
                                                            Compact cars
                                                            Midsize cars
                                                                                                 • The bottom of the market sub-compact cars
                                                                                                            Ram 1500
                                                            Large cars                           have high risk for their own driver.
                                                  125
                                                            Minivans                             • The top of the market sub-compact cars have
             in all 2-vehicle crashes




                                                                                           Dakota
                                                            Pickup trucks                        low risk for their own driver.
                                                                                                                       F-150
                                                            SUVs                                 • Both kinds of sub-compact cars have low risk
                                                  100       Sports cars                               Marquis, Malibu,
                                                                                                                             Chevy/GMC
                                                                                                 for other drivers. C/K 1500
                                                                                                       Taurus/Sable,
                                                                                                               Grand Prix
                                                                                          Tahoe
                                                                                                                                 Ranger
                                                   75
                                                                   Chevy Suburban
                                                                                                                  Explorer   Tacoma
                                                                                         Astro Van
                                                                           Expedition          Cherokee       TownCar,                                    S-10
                                                                                                                       Wrangler Blazer
                                                        Caravan, Windstar,                                    Lumina
                                                   50                                   Altima Intrepid                                Mustang
                                                                                                        4Runner
                                                           Town & Country    G Cherokee
                                                                                                                                Grand Am             Neons
                                                                               Venture Deville                      Stratus                Cavalier/
                                                                                                             Sentra              Escort/                         Corvette
                                                                                                                                           Sunfire
                                                                              Camry        626                  LeSabre, Corolla Tracer
                                                   25         CR-V
                                                                       Avalon               Legacy
                                                                                  Jetta                Civic Saturn
                                                                                     Accord,
                                                                                     Maxima          Century
                                                    0
                                                        0           25             50             75                100          125         150           175        200
                                                                             Risk to drivers in vehicle by named model in all crashes
                                                        Risks: Driver Deaths/Year per Million Vehicles
                                                  175                                    (most-popular models 1997-2001) Models: 2001 - 2005
                                                                                               Excursion             SUV
                                                                                                             Yukon
                                                                                                                        Bigger area, bigger societal risk
Risk to drivers of other vehicle by named model




                                                  100      Subcompact cars
                                                  150
                                                           Compact cars                                         Outlander
                                                                                                                                                            Rodeo
                                                   90             Hummer/H2
                                                           Midsize cars                                         Ram 1500
                                                           Large cars                    Explorer                                                         Compact SUVs
                                                  125                                                         Tahoe
                                                   80      Minivans                                                                                       Midsize SUVs
             in all 2-vehicle crashes




                                                                          Durango           Dakota                                                        Large SUVs
                                                           Pickup
                                                        M/ML Class trucks                                                F-150
                                                   70      SUVs        Navigator                    Chevy Suburban                                        Compact CSUVs
                                                  100      Sports cars
                                                                                                                                   Chevy/GMC
                                                                                                          Marquis, Malibu, Blazer/Trailblazer             Midsize CSUVs
                                                                                Cherokee/Liberty       Jimmy/Envoy                 C/K 1500
                                                   60                                                      Taurus/Sable,
                                                                            Tribute                          Grand Prix                              Vitara/Grand Vitara
                                                                                             Tahoe       GMC Suburban/Yukon XL
                                                              4Runner         Expedition                                           Ranger
                                                   50
                                                   75                                                                         Aztek
                                                                    Chevy Suburban
                                                                              Murano                  Rendezvous
                                                              Pilot                                             Explorer     Tacoma
                                                                                           Astro Van                  Sorento     Wrangler
                                                   40    Sequoia,           Expedition           Cherokee        TownCar,                                     S-10
                                                         RX300/33           Element                                        Wrangler Blazer
                                                        Caravan, Windstar,                                       Lumina
                                                                                                             Pathfinder, Grand Cherokee, Escalade
                                                   50                                     Altima Intrepid                                  Mustang
                                                                                                           4Runner
                                                   30    X5
                                                           Town & Country     G Cherokee
                                                                                      Xterra                                        Grand Am             Neons
                                                                 Highlander                                      Mountaineer, Vue
                                                                                                                        Stratus                        Tracker
                                                                                Venture Deville                                                Cavalier/
                                                                                                                                     Escort/                             Corvette
                                                   20            MDX                                             Sentra                        Sunfire
                                                   25         CR-V
                                                                              CR-V
                                                                               Camry     Jetta
                                                                                             626                   LeSabre, Corolla Tracer
                                                                                                               Escape, Forester, Discovery
                                                                        Avalon                Legacy
                                                                                    Jetta                 Civic Saturn
                                                   10                                                Santa Fe, RAV4
                                                                                       Accord,
                                                                                       Maxima        Century
                                                   0
                                                        0    10      20
                                                                     25      30     40
                                                                                    50      50       60
                                                                                                     75         80
                                                                                                            70 100          90 125 110 150 130 175
                                                                                                                                100     120              160
                                                                                                                                                140 150 200
                                                                              Risk to drivers in vehicle by named model in all crashes
                                                        Risks: Driver Deaths/Year per Million Vehicles
                                                  175                                   (most-popular models 1997-2001)

                                                                                                                               - Is weight the key factor?
                                                                                                                               - What about crash test rating?
Risk to drivers of other vehicle by named model




                                                  150       Subcompact cars
                                                            Compact cars
                                                            Midsize cars                                       Ram 1500
                                                            Large cars
                                                  125
                                                            Minivans
             in all 2-vehicle crashes




                                                                                           Dakota
                                                            Pickup trucks
                                                                                                                            F-150
                                                            SUVs
                                                  100       Sports cars                                  Marquis, Malibu,
                                                                                                                                    Chevy/GMC
                                                                                                                                    C/K 1500
                                                                                                          Taurus/Sable,
                                                                                          Tahoe            Grand Prix
                                                                                                                                    Ranger
                                                   75
                                                                   Chevy Suburban
                                                                                                               Explorer      Tacoma
                                                                                         Astro Van
                                                                           Expedition          Cherokee       TownCar,                                    S-10
                                                                                                                       Wrangler Blazer
                                                        Caravan, Windstar,                                    Lumina
                                                   50                                   Altima Intrepid                                Mustang
                                                                                                        4Runner
                                                           Town & Country    G Cherokee
                                                                                                                                Grand Am             Neons
                                                                               Venture Deville                      Stratus                Cavalier/
                                                                                                             Sentra              Escort/                         Corvette
                                                                                                                                           Sunfire
                                                                              Camry        626                  LeSabre, Corolla Tracer
                                                   25         CR-V     Avalon               Legacy
                                                                                  Jetta                Civic Saturn
                                                                                     Accord,
                                                                                     Maxima          Century
                                                    0
                                                        0           25             50               75           100                125         150        175        200
                                                                             Risk to drivers in vehicle by named model in all crashes
     Consumer Report Safety Rating      The Curb Weight by Car Model
   by Car Model as an Indicator of Risk     as an Indicator of Risk
                  200
Risk to drivers



                               38 cars  29 cars
                  180
                               2
                              R = 0.40 R2 = 0.48
                                                                     Neon


                  160


                  140


                  120


                  100


                  80

                                                                                            Regal
                  60
Risk to drivers




                  40


                  20


                   0
                         0
                        0.0      2000.5   400   1.0   600   1.5800          1000
                                                                             2.0   1200
                                                                                      2.5   1400 3.0 1600     1800
                                                                                                            3.5      2000
                                                                                                                      4.0

                         two tons - Curb Weight (in pounds)                                         CRSAmax - CRSA
                                          The Inverse of Price of a 5-Year Old Car Model
                                                   is the Best Indicator of Risk
                  200

                            38 cars
                  180
                            R 2 = 0.82
                  160


                  140
Risk to drivers




                  120


                  100


                   80


                   60


                   40


                   20


                    0
                        0         High Price
                                  25       50          75      100      125      150     175     Low Price 225
                                                                                                  200

                                         1/P, where P is the retail price of MY98 cars in 2003
Historical Safety Record
Vehicle Design and the
Physics of Traffic Safety
     Professor Marc Ross
     University of Michigan
   Email: mhross@umich.edu
1. Strong passenger compartment to inhibit
   intrusion
2. Avoid large differences in vehicle structure
   (height, rigidity, mass)
3. Convert kinetic energy into crush energy
   (structural interaction)

				
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