The Hurt Report, published in 1981 and based on accident data gathered in the 1970's, concluded that lane splitting reduces rear end crashes and improves motorcycle safety. FARS data from the United States Department of Transportation shows that rear end collisions with motorcycles are 30% lower in California (the only US state where it is legal) than in Florida or Texas, states with similar riding seasons and populations.
The Oxford Systematics report commissioned by VicRoads, the traffic regulating authority in Victoria, Australia, found that for motorcycles filtering through stationary traffic "No examples have yet been located where such filtering has been the cause of an incident.
In the United Kingdom, Motorcycle Roadcraft, the police riding manual is explicit about the advantages of filtering but also states that "The advantages of filtering along or between stopped or slow moving traffic have to be weighed against the disadvantages of increased vulnerability while filtering". The manual goes on to offer advice about things to watch out for and anticipate while filtering.
There are very few studies relevant to lane filtering, behaviour, risk or capacity. Some that are helpful include:
Halcrows for the UK Department of Transport, which examined weaving behaviours in London traffic, a series of reports led by WSP with RAND and Oxford Systematics participation also for the UK DoT.
WSP Policy and Research UK, Motorcycles and congestion: the effect of modal shift: Phase 3 policy testing. 2004, WSP for Uk Department for Transport: Cambridge UK. p. 44.
WSP Policy and Research UK, Motorcycles and congestion: the effect of modal shift: Phase 2 - Modelling Methodology. 2004, WSP for Uk Department for Transport: Cambridge UK. p. 47.
WSP Policy and Research UK, et al., Motorcycles and congestion: the effect of modal shift: Summary Final Report. 2004, WSP for Uk Department for Transport: Cambridge UK. p. 26.
All available from the Uk DoT websites with and executive summary at http://www.dft.gov.uk/pgr/regional/policy/motorcycles/motorcyclesandcongestionthee3728, and the Transportation Research Board Record publication:
Burge, P., et al., The modelling of motorcycle ownership and usage: a UK study. Transportation Research Record J Transportation Research Board, 2007(2031): p. 59-68.
This set of reports examined the choices made by commuter riders in London including lane width, for an analysis of the effects of motorcycles in congested areas.
This area is still severely under-researched.