single accident. This type of accident is often called "The Big One". Comparison with road racing Oval track racing requires different tactics than road racing. While the driver doesn't have to shift gears nearly as frequently, brake as heavily or as often, or deal with turns of various radii in both directions as in road racing, drivers are still challenged by negotiating the track. Where there is generally one preferred line around a road course, there are many different lines that can work on an oval track. The preferred line depends on many factors including track conditions, car set-up, and traffic. The oval track driver must choose which line to use each time they approach a corner. On a short track in a 25-lap feature race, a driver might not run any two laps with the same line. Both types of racing place physical demands on the driver. A driver in an IndyCar race at Richmond International Raceway may be subject to as many lateral g-forces (albeit in only one direction) as a Formula One driver at Silverstone. Weather also plays a different role in each discipline. Road racing offers a variety of fast and slow corners that allow the use of rain tires. Paved oval tracks generally don't run with a wet track surface. Dirt ovals will sometimes support a light rain. Some tracks (e.g., Evergreen Speedway in Monroe, WA) have "rain or shine" rules requiring races to be run in the rain. Safety has also been a point of difference between the two. While a road course usually has abundant run-off areas, gravel traps, and tire barriers, oval tracks usually have a concrete retaining wall separating the track from the fans. Innovations have been made to change this, however. The SAFER barrier was created to provide a less dangerous alternative to a traditional concrete wall. The barrier can be retrofitted onto an existing wall or may take the place of a concrete wall completely. Track classification Oval tracks are classified based upon their size, surface, banking, and shape. By size Their size can range from only a few hundred feet to over two and a half miles. The definitions used to differentiate track sizes have changed over the years. While some tracks use terms such as "speedway" or "superspeedway" in their name, they may not meet the specific definitions used in this article. Short track A short track