Michael C. Frick

Involvement of older drivers in multivehicle side-impact crashes

Side impacts were studied using three separate analyses. National Accident Sampling System (NASS) and National Crash Severity Study (NCSS) cases were reviewed on multivehicle crashes involving fatal chest and abdominal injury by interior contact. Twenty-five cases were analyzed and showed an unusually high involvement of older occupants. Analyses of the 1975-1986 FARS confirmed an overinvolvement. Sixty-four percent of near-side seated occupants were over 50 years old and 36% over 70 in fatal multivehicle side impacts. In contrast, 26% of victims in single-vehicle frontal crashes were over 50 and 8% over 70 years old. Analysis of the 1982-1986 NASS showed that single-vehicle side impacts are not an important injury risk for older drivers, except on icy or wet roads. In contrast, the risk of injury in multivehicle side impacts increases steadily with age and is a major problem for older drivers. The individual NASS and NCSS cases also showed that 88% of the multivehicle side crashes took place at an intersection and that the driver of the struck vehicle frequently caused the crash by driving error (48%) or traffic violation (16%). The majority of cases occurred in daylight hours, on dry roads, and without alcohol involvement. Changes in visual perception, judgment and attention of the older driver may be factors in their missing a traffic signal or turning in front of traffic under the right-of-way. In addition, a reduced tolerance to impact force probably contributes to the injury. Although an analysis of photographs of the side-impacted vehicle indicated that 44% had side-structure deformation that was similar to that produced in the National Highway Traffic Safety Administration (NHTSA) moving deformable barrier test, only 24%-32% of the cases actually addressed the proposed NHTSA dynamic side-impact test. The results of this analysis bear on the agencys preliminary regulatory impact analysis.

Seating position in cars and fatality risk

Fatality risk in passenger cars according to seating position (front versus rear; left versus center or right) was examined using Fatal Accident Reporting System (FARS) data for 1975 through 1985. Comparing the fatality risk of unrestrained occupants matched in sex and age (within three years) revealed effects attributable to seating position, and not to occupant characteristics correlated with use of different seats. Fatality risk to drivers was the same as fatality risk to right front passengers to within 1 per cent; this was so for crashes in all directions and for frontal crashes. Fatality risk in rear seats was (26 +/- 2) per cent lower than in front seats, and lower in center compared to outboard seats by (22 +/- 4) per cent for front seats and (15 +/- 4) per cent for rear seats. The center rear seat was associated with the lowest fatality risk.

Helmet effectiveness in preventing motorcycle driver and passenger fatalities

Helmet effectiveness in preventing fatalities to motorcycle drivers and passengers was determined by applying the double pair comparison method to the Fatal Accident Reporting System (FARS) data for 1975 through 1986. Motorcycles with a driver and a passenger, at least one of whom was killed, were used. In order to reduce as much as possible potentially confounding effects due to the dependence of survivability on sex and age, the analysis is confined to male drivers (there were insufficient female driver data), and to cases in which the driver and passenger age do not differ by more than three years. Motorcycle helmet effectiveness estimates are found to be relatively unaffected by performing the analyses in a number of ways different from that indicated above. It was found that helmets are (28 +/- 8)% effective in preventing fatalities to motorcycle riders (the error is one standard error), the effectiveness being similar for male and female passengers, and similar for drivers and passengers. An additional result found was that the fatality risk in the driver seat exceeds that in the passenger seat by (26 +/- 2)%. The 28% effectiveness found generates calculated fatality increases from repeal of mandatory helmet-wearing laws that are compatible with observed increases.

CAR SIZE OR CAR MASS: WHICH HAS GREATER INFLUENCE ON FATALITY RISK?

OBJECTIVES Proposed increases in corporate average fuel economy standards would probably lead to lighter cars. Well-established relationships between occupant risk and car mass predict consequent additional casualties. However, if size, not mass, is the causative factor in these relationships, then decreasing car mass need not increase risk. This study examines whether mass or size is the causative factor. METHODS Data from the Fatal Accident Reporting System are used to explore relationships between car mass, car size (as represented by wheelbase), and driver fatality risk in two-car crashes. RESULTS When cars of identical (or similar) wheelbase but different mass crash into each other, driver fatality risk depends strongly on mass; the relationship is quantitatively similar to that found in studies that ignore wheelbase. On the other hand, when cars of similar mass but different wheelbase crash into each other, the data reveal no dependence of driver fatality risk on wheelbase. CONCLUSIONS Mass is the dominant causative factor in relationships between driver risk and car size in two-car crashes, with size, as such, playing at most a secondary role. Reducing car mass increases occupant risk.

Safety belt effectiveness in preventing driver fatalities versus a number of vehicular, accident, roadway, and environmental factors☆

Safety belt effectiveness in preventing fatalities to drivers is examined versus 13 vehicle, accident or environmental factors by applying the double pair comparison method to appropriate subsets of the Fatal Accident Reporting System (FARS) data. For each factor safety belt effectiveness (the percent of fatally injured unbelted drivers who would not have been killed if they had been wearing belts) is estimated, as is an associated standard error of the estimate. The graphically presented results provide no evidence that safety belt effectiveness is systematically influenced by most of the factors investigated, including car mass and model year. The largest effect found was that safety belt effectiveness for single car crashes was (62 ±5)% compared to (30 ± 8)% for two-car crashes.

Car mass and fatality risk: has the relationship changed?

OBJECTIVES The finding that the relative safety disadvantage of small compared with large cars is less for post-1980 cars than for pre-1980 cars has stimulated speculation that increasing fuel economy standards would increase fatalities less than previously expected. Fatal crashes between two cars of similar model year were examined to see whether this would be the case. METHODS Driver fatality risk in relation to car mass was examined with Fatal Accident Reporting System data for crashes between two cars of a specific model year. RESULTS The relative risk for driver fatality in the lighter car compared with the other drivers risk in a car 50% heavier was as follows: for 1966 through 1979 cars, the risk was between 3.7 and 5.1; for 1984 cars, 2.6; and for 1990 cars, 4.1. CONCLUSIONS The results suggest that the lesser mass effect observed for mid-1980s cars occurred because improved crashworthiness features appeared in small cars earlier than in large cars. As all cars are redesigned, the relationship between risk and mass can be expected to approach that observed earlier in pre-1980 cars. If so, future fatality increases from fuel economy increases will be greater than estimated on the basis of mid-1980 data.

Potential fatality reductions through eliminating occupant ejection from cars

The percent of occupant fatalities preventable by eliminating ejection is calculated using Fatal Accident Reporting System (FARS) data for 1975 through 1986. The calculation requires estimates of two quantities. First, the fraction of all fatally injured occupants who were ejected; this is obtained directly from the FARS data. Second, the probability that an ejected occupant was killed compared to the probability that the occupant would have been killed in a similar crash in the absence of ejection; this quantity is estimated using the double pair comparison method, and its dependence on occupant age and sex and on car mass and model year is examined. High precision estimates of the reduction in fatalities that would result from eliminating ejection as functions of these same variables are thereby obtained. These estimates depend on assuming that whatever method is used to prevent ejection would cause the formerly ejected occupant to acquire the same fatality risk as a nonejected occupant in a similar crash; the study does not address how to prevent ejection. It is concluded that ejection elimination would decrease fatalities to unrestrained car occupants by 18 +/- 1%. The fatality reductions are independent of car seating position (19%, 19%, 17%, 16%, 19%, and 18% for drivers, middle front, right front, left rear, middle rear, and right rear passengers, respectively); they decrease with driver age, from 25% at age 18 years to 7% at 70 years; they decrease with increasing mass, but remained relatively independent of car model year since the early 1970s, being somewhat higher for earlier model years.

Impact of manufacturing response time on retailer inventory

Retailers receiving items from a manufacturer carry inventory to meet customer demand. As items are sold, a retailer orders new items to replenish the inventory. Once an order is placed, there is a time taken for the items to be delivered to the retailer. This time is the manufacturing response time. It includes processing, production, and delivery times. These different components of time can result in response times that are long and uncertain. This paper develops a queueing model for analysing how manufacturing response time affects the inventory needed at retailers to meet demand. The model accounts for variability in response times and allows for products to be delivered to a retailer in a different sequence than they were ordered. Simple equations are derived for the average inventory in terms of demand and response time parameters. The equations show how shortening average response time can substantially reduce retailer inventory.

Relative fatality risk in different seating positions versus car model year

Fatality risk of drivers compared to right-front passengers is examined vs. car model year (MY) using Fatal Accident Reporting System (FARS) data for 1975 through 1986. Confounding effects are removed by comparing unrestrained occupants matched in sex and age (to within three years). MY greater than or equal to 1968 cars, which complied with Federal Motor Vehicle Standard 203 (impact protection for the driver) and FMVSS 204 (rearward column displacement), are compared to MY less than or equal to 1966 cars, which did not comply with these standards. It is found that, compared to right-front passengers in the same cars, drivers had higher relative fatality risks in MY greater than or equal to 1968 cars and lower relative fatality risks in MY less than or equal to 1966 cars. Because there are so few fatal frontal crash data for MY 1966 and MY 1968 cars, definitive conclusions regarding the effectiveness of FMVSS 203 and 204 in reducing driver fatalities are not possible. However, our analysis, together with the assumption that right-front-passenger fatality risk was the same in 1966 and 1968 MY cars, does suggest that a previous 12% effectiveness estimate is more likely to be high than low.

Optimizing New-Vehicle Inventory at General Motors

This paper describes how General Motors (GM) uses operations research to optimize its new-vehicle inventory. The solution answers two complementary questions: (1) what is the optimal number of vehicles to build? and (2) what are the optimal vehicle configurations? To answer the first question, for each vehicle model, we find the inventory that maximizes profit less inventory carrying costs, which differs from the standard approach of finding the inventory needed to satisfy a given fill rate. To answer the second question, we provide a decision support tool to help dealers order the best variations for each vehicle model using a set-covering philosophy, which differs from the standard approach of recommending the highest-selling variants. This paper describes the business processes surrounding these decisions, how the need for implementation and ongoing use guided our solution development, and the impact on the business.