A recent and thorough Johns Hopkins study investigates the impacts of lane widths on traffic safety. City streets are the largest percentage of public space in most American cities, yet they are still treated as car sewers - optimized for the orderly and convenient flow of automobiles. Scrutinizing the design of these critical public spaces (including lane widths), so that they can be rebalanced to accommodate all modes safely, is paramount to building good urban places for everyone.
This study provides yet more credible evidence of the importance of narrow travel lanes on urban streets.
Check out the full Public Square article that includes some informative links to other studies and commentary.