Low Mileage Research Articles

Hydromethane: A bridge towards the hydrogen economy or an unsustainable promise?

Last decade enthusiasm about hydrogen-based economy on FC has partially been lost and spotlight is now back on using pure hydrogen or hydrogen mixtures in ICE. Pure hydrogen use in spark ignition (SI) ICE requires a dedicated engine design to optimize the high speed flame and the high pressure and temperature inside the combustion chamber. But, on the other end, may lead to high exhaust emissions of nitrogen oxides NOx. Moreover, hydrogen fueled vehicles also suffer of a very low mileage due to the very low energy density of the fuel, since hydrogen as a compressed gas at 200 atmospheres and ambient temperature has around 5% of the energy of gasoline of the same volume.All these motivations, together with the now capillary diffusion of natural gas (NG) distribution for residential and transportation purposes (especially in Europe) is making more and more interesting the option of H2 using as an additive to natural gas: NG powered vehicles, in fact, reached a very high maturity with high reliability and environmental performances. In recent years experimentations were conducted in many laboratories and research centers to verify the positive effects of hydrogen when blended with natural gas. The maturity achieved by H2–NG mixtures is also stated by commercialized gas which is available in USA with the registered trademark of Hythane® (a mixture of 20% H2–80% NG in volume).In this paper the hydro-methane option is fully outlined, a complete energy analysis and environmental sustainability is realized, considering all the main possible options available in mixture production and final use.

Skyline queries on keyword-matched data

Given a set of d-dimensional tuples with textual descriptions, a keyword-matched skyline query retrieves a skyline computed from tuples whose textual descriptions contain all query words. For example, suppose a customer prefers cars with low mileage and low price, and finds a car equipped with ‘air bag’ and ‘sunroof’ in an online shop. In such a case, a keyword-matched skyline query is highly recommended. Although there are many applications for this type of query, to date there have not been any studies on the keyword-matched skyline queries. In this paper, we define a keyword-matched skyline query and propose an efficient and progressive algorithm, named Keyword-Matched Skyline search (KMS). KMS utilizes the IR2-tree as an index structure. To retrieve a keyword-matched skyline, it performs nearest neighbor search in a branch and bound manner. While traversing the IR2-tree, KMS effectively prunes unqualified nodes by means of both spatial and textual information of nodes. To demonstrate the efficiency of KMS, we conducted extensive experiments in various settings. The experimental results show that KMS is very efficient in terms of computational cost and I/O cost.

Determining the Frequency of Asbestos Use in Automotive Brakes from a Fleet of On-Road California Vehicles

Asbestos is a known human carcinogen, and recent regulation in California limits asbestiform fibers in brakes to trace levels beginning in 2014, although there is no corresponding federal requirement. In order to gauge the current prevalence of asbestos use in automotive brake applications, the California Air Resources Board tested brake linings from 137 light- and medium-duty vehicles and 54 heavy-duty vehicles. Only about 3% of the light- and medium-duty vehicle brake linings contained chrysotile asbestos. All of those brake linings were drum-type shoes, which are generally being phased out. No asbestos was found in low mileage vehicles presumed to have their original stock linings from the vehicle manufacturer. Additionally, no asbestos was found in the heavy-duty vehicle brake shoe linings sampled. Given the small percentage of vehicle brake linings with asbestos observed, it appears that the prior federal ban that was subsequently overturned, in combination with a threat of litigation, has reduced asbestos use in brake linings. However, our study was limited in scope and without a national ban, the current and future prevalence of asbestos in brakes is uncertain, suggesting the need for continued monitoring of materials released as toxic air contaminants in normal braking operations.

Is EMG of the Lower Leg Dependent on Weekly Running Mileage?

Neuromuscular activity of the lower leg is dependent on the task performed, speed of movement and gender. Whether training volume influences neuromuscular activity is not known. The EMG of physically active persons differing in running mileage was analysed to investigate this. 55 volunteers were allocated to a low (LM: < 30 km), intermediate (IM: > 30 km & < 45 km) or high mileage (HM: > 45 km) group according to their weekly running volume. Neuromuscular activity of the lower leg was measured during running (3.33 m·s - 1). Mean amplitude values for preactivation, weight acceptance and push-off were calculated and normalised to the mean activity of the entire gait cycle.Higher activity in the gastrocnemius group was observed in weight acceptance in LM compared to IM (+30%) and HM (+25%) but lower activity was present in the push-off for LM compared to IM and HM. For the peroneal muscle, differences were present in the push-off where HM showed increased activity compared to IM (+24%) and LM (+60%). The tibial muscle revealed slightly lower activity during preactivation for the high mileage runners. Neuromuscular activity differs during stance between the high and intermediate group compared to low mileage runners. Slight adaptations in neuromuscular activation indicate a more target-oriented activation strategy possibly due to repetitive training in runners with higher weekly mileage.

Speed‐dependent emission of air pollutants from gasoline‐powered passenger cars

In Korea emissions from motor vehicles are a major source of air pollution in metropolitan cities, and in Seoul a large proportion of the vehicle fleet is made up of gasoline‐powered passenger cars. The carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) and carbon dioxide (CO2) contained in the exhaust emissions from 76 gasoline‐powered passenger cars equipped with three‐way catalysts has been assessed by vehicle speed, vehicle mileage and model year. The results show that CO, HC, NOx and CO2 emissions remained almost unchanged at higher speeds but decreased rapidly at lower speeds. While a reduction in CO, HC and NOx emissions was noticeable in vehicles of recent manufacture and lower mileage, CO2 emissions were found to be insensitive to vehicle mileage, but strongly dependent on gross vehicle weight. Lower emissions from more recent gasoline‐powered vehicles arose mainly from improvements in three‐way catalytic converter technology following strengthened emission regulations. The correlation between CO2 emission and fuel consumption has been investigated with a view to establishing national CO2 emission standards for Korea.

Cold‐start and chemical characterization of emissions from mobile sources in Mexico

In this work tailpipe and evaporative emissions from a set of normal and high emitter vehicle models, year 2006–2008 (low mileage) certified when new to meet the Tier 1 emission standard, were characterized for criteria pollutants (carbon monoxide, nitrogen oxides and hydrocarbons), and a suite of unregulated emissions including aliphatic and aromatic aldehydes, monocyclic aromatic compounds, 1,3 butadiene, n‐hexane and acrolein. Data were obtained under the three different driving conditions of the United States Federal Test Procedure, FTP‐75 cycle. High emissions of both regulated and unregulated pollutants were observed in the cold‐start phase of the driving cycle for low mileage Tier 1 normal and high emitters engines. Data were compared with results obtained for a set of MY >1992–2005 that included vehicles with no catalytic converters, Tier 0 and MY 2000–5 Tier 1 emission standard with high mileage. The calculated average cold‐start emissions for normal emitters in grams are 0.93, 8.21 and 1.06 for NMHC CO, and NOx, respectively for Tier 1 low mileage vehicles. The reductions in emissions for Tier 1 normal emitters are 76%, 56% and 56% for NMHC, CO and NOx, respectively, but 58%, 30% and 25% for the high emitters. Differences in emission can be ascribed to the mileage accumulation more than technological improvements. Cold‐start emissions account in the USA roughly 10% of emissions from gasoline‐powered vehicles. In Mexico the fractions are likely to be higher because one must account also for the contribution of Tier 0 and the running exhausts emissions of vehicles with no catalytic converters.

A field operational test on valve-regulated lead-acid absorbent-glass-mat batteries in micro-hybrid electric vehicles. Part II. Results based on multiple regression analysis and tear-down analysis

In the first part of this work [1] a field operational test (FOT) on micro-HEVs (hybrid electric vehicles) and conventional vehicles was introduced. Valve-regulated lead-acid (VRLA) batteries in absorbent glass mat (AGM) technology and flooded batteries were applied. The FOT data were analyzed by kernel density estimation. In this publication multiple regression analysis is applied to the same data. Square regression models without interdependencies are used. Hereby, capacity loss serves as dependent parameter and several battery-related and vehicle-related parameters as independent variables. Battery temperature is found to be the most critical parameter. It is proven that flooded batteries operated in the conventional power system (CPS) degrade faster than VRLA–AGM batteries in the micro-hybrid power system (MHPS).A smaller number of FOT batteries were applied in a vehicle-assigned test design where the test battery is repeatedly mounted in a unique test vehicle. Thus, vehicle category and specific driving profiles can be taken into account in multiple regression. Both parameters have only secondary influence on battery degradation, instead, extended vehicle rest time linked to low mileage performance is more serious.A tear-down analysis was accomplished for selected VRLA–AGM batteries operated in the MHPS. Clear indications are found that pSoC-operation with periodically fully charging the battery (refresh charging) does not result in sulphation of the negative electrode. Instead, the batteries show corrosion of the positive grids and weak adhesion of the positive active mass.

수입 음식료품의 푸드 마일리지 및 이산화탄소 배출량 산정

Increase in greenhouse gas emissions during the last century has led to remarkable changes in our environment and climate system. Many policy measures have been developed to reduce greenhouse gas emissions across the world, many of which require our lifestyle changes from energy-intensive to energy-saving. One of the changes in our living patterns is to consider food miles. A food mile is the distance food travels from where it is produced to where it is consumed. Providing information of food miles will help people choose low mileage food, helping promote a "green consumption" action and lead to a low carbon society with emission reduction systems. In this study, 10 items are selected from 23 Harmonized commodity description and 2-digit coding system (HS) to estimate their food miles, and <TEX>$CO_2$</TEX> emissions released in the transportation of imported food. For the estimation, four countries are chosen-Korea, Japan, United Kingdom (UK) and France, with Korea and Japan's 2001, 2003, and 2007 trade statistics and UK and France's 2003 and 2007 trade statistics used. As a result, Korea showed in 2007 the highest level of food miles and <TEX>$CO_2$</TEX> emissions per capita among 4 countries. That suggests that Korea should make an effort to purchase local food to reduce food miles and use low-carbon vehicles for food transport, contributing to reducing greenhouse gas emissions.

Basic Research on a Novel Zero-Emission Public Transportation System (Design of Charge-Boosting System for an Electric Bus System Charged at Every Bus Stop)

In a sustainable city, public transportation is prohibited from emitting greenhouse gasses. To reduce emissions of carbon dioxide, a major greenhouse gas, a vehicle running on electric power generated from a green energy source is optimal because it does not emit carbon dioxide. With this goal in mind, we propose a public transport system consisting of electric buses that are charged intermittently at every bus stop using electric power generated from green energy sources. Such a system resolves the problem of low mileage per charge for heavy batteries. This system would also be able to effectively use low-density and widely available solar energy for generating power at bus stops that are widely distributed throughout a city. One major problem in realizing this system is the development of the charge-boosting system. And lightning of the storage device mounted on the bus is also key problem. We therefore begin by examining the features of typical storage devices. Next, we investigate issues involving the design of the charge-boosting system at the bus stop and the storage device on the bus. Finally, we perform a model experiment using a single-passenger electric vehicle. We find that a vehicle containing a designed storage device and running on electric power generated from solar energy can repeat the cyclical operation of running for approximately 90 s, stopping 20 s for charge, and accelerating fully charged from the bus stop for 4 s. The result is that the model experiment validates the proposed transport system design.

Nitrous oxide emissions from light duty vehicles

Nitrous oxide (N 2O) emissions measurements were made on light duty gasoline and light duty diesel vehicles during chassis dynamometer testing conducted at the Environment Canada and California Air Resources Board vehicle emissions laboratories between 2001 and 2007. Per phase and composite FTP emission rates were measured. A subset of vehicles was also tested using other driving cycles to characterize emissions as a function of different driving conditions. Vehicles were both new (<6500 km) and in-use (6500–160,000 km) and were tested on low sulfur gasoline (<30 ppm) or low sulfur diesel (<300 ppm). Measurements from selected published studies were combined with these new measurements to give a test fleet of 467 vehicles meeting both US EPA and California criteria pollutant emissions standards between Tier 0 and Tier 2 Bin 3 or SULEV. Aggregate distance-based and fuel-based emission factors for N 2O are reported for each emission standard and for each of the different test cycles. Results show that the distinction between light duty automobile and light duty truck is not significant for any of the emission standards represented by the test fleet and the distinction between new and aged catalyst is significant for vehicles meeting all emission standards but Tier 2. This is likely due to the relatively low mileage accumulated by the Tier 2 vehicles in this study as compared to the durability requirement of the standard. The FTP composite N 2O emission factors for gasoline vehicles meeting emission standards more stringent than Tier 1 are substantially lower than those currently used by both Canada and the US for the 2005 inventories. N 2O emission factors from test cycles other than the FTP illustrate the variability of emission factors as a function of driving conditions. N 2O emission factors are shown to strongly correlate with NMHC/NMOG emission standards and less strongly with NO X and CO emission standards. A review of several published reports on the effect of gasoline sulfur content on N 2O emissions suggests that additional research is needed to adequately quantify the increase in N 2O emissions as a function of fuel sulfur.

In defence of the ‘low-mileage bias’

There has been a long-recognised association between extent of driving and crash involvement: the lower the annual mileage driven, the higher the per-distance crash rate. Because older drivers generally drive less distance per year than others, this association has been used to explain much of their apparent over-involvement in crashes. Several studies from different countries around the world have demonstrated this ‘low-mileage bias’ and the relative safety of older drivers. However all studies have relied upon self-reported crash involvement and driving activity. Staplin et al. [Staplin, L., Gish, K., Joyce, J., 2008. ‘Low mileage bias’ and related policy implications—a cautionary note. Accident Analysis and Prevention 40, 1249–1252] have drawn attention to the discrepancy between self-reported and odometer-based driving distances and have argued against the credibility of the low-mileage bias. This paper has re-worked initial data from an early study which supported low-mileage bias, this time using odometer-based readings rather than self-reported mileage. Accepting the odometer readings at face value, the low-mileage bias remains evident, albeit at a reduced level.

‘Low mileage bias’ and related policy implications—A cautionary note

This research examined a relationship asserted in recent literature in the field of traffic safety and injury prevention—that a significant indicator for elevated crash risk among older drivers, and potential trigger for individualized assessment at license renewal, is a low (<3000 km) annual driving distance. Sampling problems in earlier reports, in particular a reliance on self-report measures of both exposure and crash involvement, are highlighted. A pattern of misestimation for those who self-report an extremely low or extremely high number of miles driven is documented, that casts serious doubt upon the effect reported earlier. The present findings underscore the need for objective exposure measures for future analyses of this nature, and impact discussions about the feasibility of this suggested strategy to aid detection of at-risk older drivers by licensing officials.

Wankel auf dem Prüfstand: Ursprung, Entwicklung, und Niedergang eines innovativen Motorenkonzeptes (review)

Reviewed by: Wankel auf dem Prüfstand: Ursprung, Entwicklung, und Niedergang eines innovativen Motorenkonzeptes Ulrich Wengenroth (bio) Wankel auf dem Prüfstand: Ursprung, Entwicklung, und Niedergang eines innovativen Motorenkonzeptes. By Ulrich Ch. Knapp . Münster: Waxmann, 2006. Pp. 213. €25.50. This book by Ulrich Ch. Knapp is a history of the Wankel rotary engine from a German perspective. Instead of reciprocating pistons, the Wankel uses a rotor for the conventional four-stroke process of most gasoline-powered engines. Beginning in the mid-1960s, Wankel engines were used in cars, boats, and pumps. But the only Wankel-powered automobile today is a Mazda sports car. While the Wankel engine is very compact, delivers unparalleled smooth power, and easily revs up, its shortcomings are low mileage and serious exhaust pollution. Both are consequences of the oddly shaped, moving combustion chamber that does not allow for efficient combustion. Felix Wankel (1902–1988) was a school dropout with no engineering education. In 1922 he organized a militant forerunner to the SA, and in 1926 he formally joined the Nazi Party. Upset by the personal vanities of some Nazi fat cats, he left the party in 1932 and was even a political prisoner for a few months after the Nazis' rise to power in 1933. This did not affect his anti-democratic attitude, and throughout the Nazi years he courted party leaders all the way up to Hitler to find support for his engineering experiments. His main supporter and advisor from the early 1930s until well after World War II was Wilhelm Keppler, economic adviser to the Nazi government, SS leader, undersecretary of state "for special tasks," and in the end a convicted war criminal. Bored by his job as an insurance agent, Wankel began developing rotary engines in the late 1920s in a small workshop. His experience with rotary valves earned him a number of research contracts for aircraft engines. The breakthrough for a workable rotary engine only came in the 1950s. While major automobile firms turned a cold shoulder, Wankel found support at NSU, a small manufacturer of motorcycles and subcompact cars. NSU was to develop the Wankel engine into an automobile power plant, first in a little "spider" and eventually in a (European) full-size limousine. Financially more important—and certainly more profitable—was licensing by NSU and Wankel. Virtually all major engine and auto manufacturers took a Wankel license in the late 1960s and early 1970s. The first licensee in America was Curtiss-Wright; the most promising was General Motors. But with the exception of Mazda, all of this came to nothing. The rise of oil prices after 1973 killed the low-mileage Wankel. And, more than Knapp admits, tightening pollution restrictions eventually sealed the fate of this ingenious little engine. Felix Wankel himself had been smart enough to sell his engineering firm in 1972—a year before gas prices skyrocketed—to Lonrho, a British conglomerate, for 100 million deutschmarks. There is a school of Wankel enthusiasts who claim that a "piston cartel" [End Page 652] among major car manufacturers obstructed the development of a superior technology. Knapp debunks all the conspiracy theories. He convincingly shows that it was the fundamental shortcomings of the rotary engine and the simultaneous improvement of traditional piston engines that made auto manufacturers turn away as they had previously done with gas turbines. Knapp is very good in showing how it took an innovative group of engineers at the periphery of auto manufacture to venture into a groundbreaking new technology in the first place. He follows this group and eventually finds some of them at Audi, designing a small diesel engine for Volkswagen. Diesels yield the best mileage in cars and were felt to be a godsend in the face of rising oil prices. America quickly gave up on diesel-powered autos, but in continental Europe they currently have a market share of more than 50 percent. Diesels were the answer to high fuel costs, while Wankels gave an idea of how silent a car could be. The combination of the two characteristics was the R&D path of the European car industry. Wankel engines were not ineffective, as Knapp shows, they just turned up...

Older drivers, medical condition, medical impairment and crash risk

New evidence has appeared to support the fact that the over-involvement of older drivers in traffic accidents disappears when the low mileage bias is taken into account. As a group, older drivers are as safe as or safer than other age groups, and only low mileage older drivers have a high crash rate. Furthermore, the role of the medical condition of older drivers in traffic accidents, as well as the fitness to drive evaluation, are objects of controversy. We examined all this with a cohort of 4316 drivers attending Medical Driving Test Centres for a mandatory fitness to drive evaluation. Our data shows that older drivers (≥75) have a lower crash rate. Medical conditions that impair fitness to drive, as a tendency, increased with advanced age and with lower mileage group. The multivariate analysis of variance showed that there is an effect ( p < 0.0001) of age-range and mileage on the annual crash rate per million kilometres driven, while a medical restriction (“fit to drive with restriction”) has no effect ( p > 0.05). Our data suggests that health status is not associated with increased crash risk for the low mileage group, although further studies are needed.

Driver experience and cognitive workload in different traffic environments

How do levels of cognitive workload differ between experienced and inexperienced drivers? In this study we explored cognitive workload and driver experience, using a secondary task method, the peripheral detection task (PDT) in a field study. The main results showed a large and statistically significant difference in cognitive workload levels between experienced and inexperienced drivers. Inexperienced, low mileage drivers had on average approximately 250 milliseconds (ms) longer reaction times to a peripheral stimulus, than the experienced drivers. It would, therefore, appear that drivers with better training and experience were able to automate the driving task more effectively than their less experienced counterparts in accordance with theoretical psychological models. It has been suggested that increased training and experience may provide attention resource savings that can benefit the driver in handling new or unexpected traffic situations.

Older drivers do not have a high crash risk—A replication of low mileage bias

The widespread claim that older drivers are overly involved in crashes has apparent support from crash data, especially when distance travelled is used as the exposure measure. However, independent of age, drivers travelling more kilometres will typically have lower crash rates per kilometre than those driving fewer kilometres. This paper uses Dutch travel survey data from a large sample of respondents to confirm previous research findings concerning the association between annual mileages driven and crash involvement. When the crash rates of drivers of different ages were compared after being matched for yearly driving distance, most drivers aged 75 years and above were indicatively safer than all other drivers. Only older drivers travelling less than 3000 km per year (just over 10% of all older drivers in the survey) gave any indication of elevated crash rates.

Impact of Engine Lubricant Properties on Regulated Gaseous Emissions of 2000-2001 Model-Year Gasoline Vehicles

The impact of the sulfur (S) content in lubricating oil was evaluated for four ultra-low-emission vehicles and two super-ultra-low-emission vehicles, all with low mileage. The S content in the lube oils ranged from 0.01 to 0.76%, while the S content of the gasoline was fixed at 0.2 ppmw. Vehicles were configured with aged catalysts and tested over the Federal Test Procedure, at idle and at 50-mph cruise conditions. In all testing modes, variations in the S level of the lubricant did not significantly affect the regulated gas-phase tailpipe emissions. In addition to the regulated gas-phase emissions, a key element of the research was measuring the engine-out sulfur dioxide (SO2) in near-real-time. This research used a new methodology based on a differential optical absorption spectrometer (DOAS) to measure SO2 from the lubricants used in this study. With the DOAS, the contribution of SO2 emissions for the highest-S lubricant was found to range from less than 1 to 6 ppm on a gasoline S equivalent basis over the range of vehicles and test cycles used. The development and operation of the DOAS is discussed in this paper.

From environmental excellence to sustainability

Several decades of technical accomplishments in making environmental improvements to products and processes have taught us that it is possible to achieve environmental improvements while not making real strides towards the goal of sustainability. Cleaner products, in practice, can boost demand for consumption, thus using greater per capita non-renewable natural resources. For instance, the improvement of automobile engine performance has paved the way for our propensity to drive bigger cars with lower mileage per gallon or simply to drive longer distances. A better direction for the future therefore begs for achieving sustainability than for merely improving environmental performance. Realizing the importance of resource conservation and its societal and ecological benefits, many multi-national corporations have already begun programs to address sustainable development issues. Sustainable development, however, is not limited to manufacturing systems only. Civic units, such as cities, regions, and watersheds in many parts of the world are also being evaluated from this viewpoint. These activities undertaken in the interest of sustainable development are in keeping with the awareness created by the World Commission on Environment and Development (WCED). As is evident, sustainability refers to a system that needs to be appropriately defined. Not all systems we can consider can be defined on the basis of global environmental, ecological and developmental attributes and metrics. Sustainability of a village cannot obviously mean the same thing as sustainability of the planet. For systems smaller than the planet Earth, care has to be taken in choosing metrics so as to assure that the metrics provide a real measure of progress towards sustainability while not adversely affecting the surroundings. When done correctly, progress towards sustainability of smaller systems will complement the sustainability of the planet. As I have attempted to show in a Perspective article published in the AIChE Journal (vol 49, no. 8, p. 1929, 2003), if we can design aggregate metrics to represent the environmental, ecological and developmental aspects of a system, we achieve real progress towards sustainability only when all three metrics show improvement independently. Finding a scientific way to devise these three aggregate metrics is, however, a difficult undertaking. The greatest challenge before scientists, technologists, and policy makers today is to devise sustainability metrics that describe quantitatively progress made in a system, be it a manufacturing process or an ecosystem. Someday in the future when we have some expertise in certifying progress towards sustainability, we would need to be able to recognize attainment of sustainability when we actually arrive there. Editorial Clean Techn Environ Policy 6 (2003) 1 DOI 10.1007/s10098-003-0237-4

Âge des conducteurs de voiture et accidents de la route: Quel risque pour les seniors ?

Increasing life expectancy and the fact that the baby boomer generation is reaching retirement age are increasing the size of the elderly population. As road users, seniors have quite specific travel behaviours, and this has an impact on accidents. This paper adopts a quantitative approach with a view to showing the specific characteristics of elderly drivers as regards travel, accidents and road risk. Towards this end it surveys a number of previous studies and takes advantage of recent data to update some of the findings of these contain. Some road risk indicators are described, and attention is paid to the methodological bias inherent in the methods employed. Our analysis shows that the presence of seniors on the roads is growing as the proportion, particularly of the women, in this group who are accustomed to driving increases. They nevertheless cover fewer kilometres than other drivers and develop compensatory strategies, for example not driving when conditions are difficult or driving more slowly than other drivers. When they have accidents they tend to be more severe because of their greater vulnerability. They have higher crash involvement at intersections as a result of detection and estimation difficulties in the driving task. The excess crash risk per kilometre driven for seniors that was observed a few years ago is tending to fall, or even disappear, if the low mileage bias is taken into account.

Driver ageing does not cause higher accident rates per km

Based on Finnish survey data, older (65+, n =1559) and younger (26–40, n =310) drivers’ accident rates were compared. In accordance with earlier studies, the rates were similar per driver (0.1) but there was a non-significant trend towards older drivers having more accidents per distance driven (10.8 vs. 8.3 per 1 million km). However, when the accidents-per-km comparison was made in groups matched for yearly exposure, there is no evidence for higher risk with increasing age. In both age groups, risk per km decreased with increasing yearly driving distance. We suggest that the previous perception of an age-related risk increase of accidents per distance driven arises from a failure to control for low mileage bias at all ages.