Lane splitting is riding a bicycle or motorcycle between lanes or rows of slow moving or stopped traffic moving in the same direction. It is sometimes called whitelining, or stripe-riding. This allows riders to save time, bypassing traffic congestion, and may also be safer than stopping behind stationary vehicles.
Filtering or filtering forward is to be contrasted with lane splitting. Lane filtering refers to motorcycles moving through traffic that is stopped, such as at a red traffic light.
In the developing world
In population-dense and traffic-congested urban areas, particularly in the developing world, the space between larger vehicles is filled with a wide variety of different kinds of two-wheeled vehicles, as well as pedestrians, and many other human or animal powered conveyances. In places such as Bangkok, Thailand and in Indonesia, the ability of motorcycles to take advantage of the space between cars has led to the growth of a motorcycle taxi industry. In Indonesia, the motorcycle is the most common type of vehicle.
Unlike typical developed nations that have only a handful of vehicle types on their roads, many types of transport will share the same roads as cars and trucks; this diversity is extreme in Delhi, India, where more than 40 modes of transportation regularly use the roads. In contrast, New York City, for example, has perhaps five modes, and in parts of America a vast majority of traffic is made up of two types of vehicles on the road: cars and trucks.
It has been suggested that highly diverse and adaptive modes of road use are capable of moving very large numbers of people in a given space compared with cars and trucks remaining within the bounds of marked lanes. On roads where modes of transportation are mingled this can cause a reduced efficiency for all modes.
Safety
Filtering forward, in stopped or extremely slow traffic, requires very slow speed and awareness that in a door zone, vehicle doors may unexpectedly open. Also, unexpected vehicle movements such as lane changes may occur with little warning. Buses and tractor-trailers require extreme care, as the cyclist may be nearly invisible to the drivers who may not expect someone to be filtering forward. To avoid a hook collision with a turning vehicle at an intersection after filtering forward to the intersection, cyclists are taught to either take a position directly in front of the stopped lead vehicle, or stay behind the lead vehicle. Cyclists should not stop directly at the passenger side of the lead vehicle, that being a blind spot.
Research
Little safety research in the United States has directly examined the question of lane splitting. The European MAIDS report studied the causes of motorcycle accidents in four countries where it is legal and one where it is not, yet reached no conclusion as to whether it contributed to or prevented accidents. Proponents of lane splitting state that the author of the Hurt Report of 1981, Harry Hurt, implied that lane splitting improves motorcycle safety by reducing rear end crashes. However, in subsequent interviews, Hurt stated that there is no factual evidence to support this claim.
Lane splitting supporters also state that the US DOT FARS database shows that fatalities from rear-end collisions into motorcycles are 30% lower in California than in Florida or Texas, states with similar riding seasons and populations but which do not lane split. No specifics are given about where this conclusion is found in the FARS system. The database is available online to the public. The NHTSA does say, based on the Hurt Report, that lane splitting "slightly reduces" rear-end accidents, and is worthy of further study due to the possible congestion reduction benefits.
Lane splitting is never mentioned anywhere in the Hurt Report, and all of the data was collected in California, so no comparison was made between of lane splitting vs. non-lane splitting. The Hurt Report ends with a list of 55 specific findings, such as "Fuel system leaks and spills are present in 62% of the motorcycle accidents in the post-crash phase. This represents an undue hazard for fire." None of these findings mentions lane splitting, or rear-end collisions. The legislative and law enforcement advice that follows this list does not mention lane splitting or suggest laws be changed with regard to lane splitting.
However lane-splitting riders who were involved in collisions were also more than twice as likely to rear-end another vehicle (38.4 percent versus 15.7 percent).