During last week's interview on WGN Radio one caller asked me why bicyclists sometimes ride in the middle of the lane, blocking passage by faster moving vehicles. I explained that in order to make themselves more visible to drivers and discourage attempts to pass dangerously close, bicyclists can and should take the lane. The idea is to encourage motorists to change lanes if they wish to pass reducing the likelihood of a dangerous miscalculation. More and more states are passing laws which prohibit drivers from passing too closely to cyclists. In Illinois, drivers must give them at least three feet of space when passing.
Recently, I came across an excellent graphic produced by iamtraffic.org which effectively demonstrates why is is so important for a cyclist to take the lane when riding on a road where the lane width is insufficient for sharing by bike and car together: