with air travel. In the United States between 2000 and 2009, train travel averaged 0.43 deaths per billion passenger miles traveled. While this was higher than that of air travel at 0.07 deaths per billion passenger miles, it was also far below the 7.28 deaths per billion passenger miles of car travel. In the 21st century, several derailments of oil trains caused fatalities, most notably the Canadian Lac-Mégantic rail disaster in 2013 which killed 47 people and leveled much of the town of Lac-Mégantic. The vast majority of train-related fatalities, over 90 percent, are due to trespassing on railroad tracks, or collisions with road vehicles at level crossings. Organizations such as Operation Lifesaver have been formed to improve safety awareness at railroad crossings, and governments have also launched ad campaigns. Trains cannot stop quickly when at speed; even an emergency brake application may still require more than a mile of stopping distance. As such, emphasis is on educating motorists to yield to trains at crossings and avoid trespassing. Motive power Before steam The first trains were rope-hauled, gravity powered or pulled by horses. Steam Steam locomotives work by using a boiler to heat water into steam, which powers the locomotive's pistons which are in turn connected to the wheels. In the mid 20th century, most steam locomotives were replaced by diesel or electric locomotives, which were cheaper, cleaner, and more reliable. Steam locomotives are still used in heritage railways operated in many countries for the leisure and enthusiast market. Diesel Diesel locomotives are powered with a diesel engine, which generates electricity to drive traction motors. This is known as a diesel–electric transmission, and is used on almost all diesels. Diesel power replaced steam for a variety of reasons: diesel locomotives were less complex, far more reliable, cheaper, cleaner, easier to maintain, and more fuel efficient. Electric Electric trains receive their current via overhead lines or through a third rail electric system, which is then used to power traction motors that drive the wheels. Electric traction offers a lower cost per mile of train operation but at a higher initial cost, which can only be justified on high traffic lines. Even though the cost per mile of construction is much higher, electric traction is cheaper to operate thanks to lower maintenance and purchase costs for locomotives and equipment. Compared to diesel locomotives, electric locomotives produce no direct emissions and accelerate much