A recent study in the UK, reported in the Guardian, showed that drivers give less room to cyclists when there is a bike lane than when there isn't. Graduate student Ciaran Meyers attached a special camera to his bike and found that motorists gave him an extra 18.1 cm (7.12 inches) when there was no marked cycle lane than they did when there was a lane.
Transport engineer John Parkin explains why:
The real purpose of bike lanes: Poutine stops for City employees
In the presence of a cycle lane, a driver is likely to drive between the cycle lane line and the centre line in a position which is appropriate for the visible highway horizontal geometry ahead of the driver. A cyclist within a cycle lane does not seem to cause a driver to adopt a different position in his or her lane. This has important implications for the width of cycle lanes and implies that their width should never be compromised.
In other words, the driver ignores the painted line and treats the bike lane as part of his turf. Perhaps this is a good reason to paint the bike lanes a different colour, as they are considering in Toronto.
According to an article in Spacing, they did this in Portland a decade ago in spots where there were common conflicts between cars and bikes.
The Portland blue bike lanes project has shown that cyclists feel 50% safer biking on the coloured lanes. Further results show there has been a 20% increase in motorists yielding for cyclists due to visibility and awareness. A similar study conducted in Denmark found that coloured bike lanes reduced bike-car collisions by 38% and reduced fatalities and serious injuries by 71%.
One can certainly see how it would make it a lot clearer to drivers; if Ciaran Meyers is correct, drivers don't even see the regular ones. More in Spacing
See also in Planet Green: Are Dedicated Cycling Lanes Better For Cyclists? Or Should We Share The Road?