DOES A TOWBAR INCREASE THE RISK OF NECK INJURY IN REAR-END COLLISIONS?

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Jane Harvey
5 years ago
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1 DOES A TOWBAR INCREASE THE RISK OF NECK INJURY IN REAR-END COLLISIONS? A STUDY BASED ON A MERGER OF DANISH ADMINISTRATIVE REGISTRIES ANNE VINGAARD OLESEN H A R R Y L A H R M A N N T H E T R A F F I C RESEARCH GROUP AT AALBORG UNIVERSITY D E N M A R K

The tow-bar A common sight in Denmark especially in rural areas Prevalence of 60% in the Motor Vehicle Registry in the period 2003-12 From seller s car database on the internet 37% in all of Denmark

2 The tow-bar A common sight in Denmark especially in rural areas Prevalence of 60% in the Motor Vehicle Registry in the period From seller s car database on the internet 37% in all of Denmark (2017) A count in typical parking lot gave a prevalence of 48% with 90% towbars actually on the car (2017) Prevalence has dropped recently because of an increase in small cars (as cars number two and else if mounting is not possible)

3 The study aim To investigate the association between the risk of neck injury in occupants of the struck car in a rear-end collision

The registry merger The National Registry of Motor Vehicles: registration plates, towbar status Police reports: personal identification numbers, registration plates, accident type The Central Person

4 The registry merger The National Registry of Motor Vehicles: registration plates, towbar status Police reports: personal identification numbers, registration plates, accident type The Central Person Registry: personal identification numbers, vital status, nationality The National Hospital Discharge Registry: personal identification numbers, diagnoses Socio-economic databases at Statistics Denmark: personal identification numbers, income, highest attained education, socioeconomic status All information available at date of accident The personal identifier and the registration plate are the central merger variables

The modern collision zone curls in rear-end collisions In order to absorb the force and protect occupants in the cabin Mounting of a stiff tow-bar frame is highly likely to inflate the curling

5 The modern collision zone curls in rear-end collisions In order to absorb the force and protect occupants in the cabin Mounting of a stiff tow-bar frame is highly likely to inflate the curling mechanism May increase the risk of neck injury in the struck car with a towbar Several ways to mount the tow-bar And now possible to demount when not using it All of which may mix the impacts of a towbar registered in a general Motor Vehicle Registry

Strong experimental evidence: Krafft et al. (2000). AAP 32: 187-95. Two Volvo 240s one with and one without a towbar Car acceleration higher in towbar equipped car with peak at 9.

6 Strong experimental evidence: Krafft et al. (2000). AAP 32: Two Volvo 240s one with and one without a towbar Car acceleration higher in towbar equipped car with peak at 9.6g Car acceleration in car without towbar had peak at 8.0g Dummy in the car with towbar experienced 33% higher peak acceleration in lower neck, 8.9g Compared with 6.7g for dummy in the car without towbar Increased risk of 22% for long-term consequences of neck injury in struck cars with a towbar (p<0.001) One other study found no effect Linder et al.?? Few other sources cite Krafft et al.(2000)??

7 Negative finding: no effect of tow-bar on neck injury Could be explained by measurement error on the information on tow-bar in the Motor Vehicle Registry: imprecise exposure erases the effect if present Counts, person-years, and neck injury rates. Public registry data from Denmark, N N P-years IR Variable Variable Persons Events in 1000s per % CI significance All year prevalence of 16% Tow-bar on struck car Yes p < No Unadjusted IRR=0.92; p=0.11 Unknown

8 Estimated hazard ratios in multivariate Cox proportional hazard regression. Hazard ratios can be interpreted as incidence rate ratios. Public registry data from Denmark, Multivariate analysis Hazard Robust Variable Variable ratio SE 95% CI P-value significance Tow-bar on struck car Yes No Unknown Adjusted for: gender, age, seat, income, education, accident type, calendar year, weight of car, first registration year

9 Sex Male p < Female Age in years p < Females have increased risk Older persons tend to underreport?

10 Seat in struck car Driver p < Passenger Household income <1st quintile p < st 2nd quintiles nd 3rd quintiles rd 4th quintiles >4th quintile Unknown Passenger seat associated with increased risk of neck injury Poor and wealthy have reduced risk

11 Highest level of education Primary education Upper secondary education Vocational Education and Training (VET) Qualifying educational programs Short-cycle higher education Vocational bachelors programs Bachelors programs Masters programs PhD programs Unknown Educational effect explained by income level etc.

12 Accident type Hit directly from the back when driving straight ahead Hit from the back when turning right Hit from the back when turning left Calendar year Reduced risk when turning right No significant effect of calendar year

13 Weight of struck car in kilograms Unknown First registration year of struck car Unknown No effect of weight and first registration year of struck car

in typical parking lot demonstrated that 90% of tow-bars were actually on the car (and not taken off) More crash test needed in order to

14 Conclusion 16% of occupants of struck cars were diagnosed with neck injury by doctors in hospitals/emergency rooms after rear-end collisions No effect of tow bar on the struck car in large study of 9370 occupants Measurement error might induce result Count of cars in typical parking lot demonstrated that 90% of tow-bars were actually on the car (and not taken off) More crash test needed in order to corroborate registry finding Could the tow-bar be associated with neglectible risk of neck injury in modern cars Law of physics does somehow rule

What we learnt from this merge Remarkable possibilities for registry merge in Denmark and Scandinavia which is of course well-known Merge by registration plate in police reports and

15 What we learnt from this merge Remarkable possibilities for registry merge in Denmark and Scandinavia which is of course well-known Merge by registration plate in police reports and Motor Vehicle Registry possible Merge by personal identifier in police reports and National Discharge Registry (hospital registry) possible Denmark is only a novice regarding registry studies

Strengths and limitations of registry studies Complete populationbased studies with many cases (likely a high power) Facilitate assessment of various hypotheses such as mix between different personal

16 Strengths and limitations of registry studies Complete populationbased studies with many cases (likely a high power) Facilitate assessment of various hypotheses such as mix between different personal injuries and diagnoses and hospital courses But - Measurement error such as on information of tow-bar status in the Motor Vehicle Registry Lack of information on confounders such as (precise) personal characteristics, attitudes and psychological profiles Missing values in some variables unknowns

17 Experiences with registry data in Scandinavia? Which kinds of merges are possible in the different countries? Experiences with different sources such as police reports with registry data? Experiences with various sorts of sources of error? How to overcome the limitations: sensitivity analyses and multiple imputation or? Other issues?

A review of 2015 fatal collision statistics as of 31 December 2015

A review of 2015 fatal collision statistics as of 31 December 2015 A review of fatal collision statistics as of 31 December This report summarises the main trends in road fatalities that have emerged in. This has been prepared by the Road Safety Authority following analysis