Evaluation of Shared Lane Markings is a FHWA sponsored report written by the UNC Highway Safety Research Center that examined this traffic control device in three cities: Cambridge, MA, Seattle, WA, and Chapel Hill, NC.
My Critique of Evaluation of Shared Lane Markings HERE provides a detailed look at the evaluation in Chapel Hill, NC.
The Shared Lane Marking “experiment” in Chapel Hill, NC achieved its objective of compelling more bicycle drivers and motorists into side-by-side same lane sharing, perverting the use of the SLM as intended by the MUTCD. The results show bicyclists operated closer to the curb and motorists passed closer and faster, with less full and partial lane changing, and more within-lane passing AFTER SLM installation.
These are not benefits to bicycle users. The changes effected by the SLMs reflect dubious benefits to motorists at bicyclists’ expense.
At 13 feet wide the lane is demonstrably physically and by AASHTO and NCDOT definitions too narrow for side-by-side use. The SLM placement was not compliant with already poor MUTCD minimum guidelines. But these deficiencies were overlooked.
The investigators seemingly went out of their way via misinterpretation, deception, errors of omission, and overt errors to frame the operational changes as beneficial for bicyclists. A microcosm of this effort is their repeated declaration that motorists operated further from the curb AFTER the SLMs were painted when no bicyclists were present, and that this reflects increased operating space and improved conditions for bicyclists when they do arrive. In contrast, when bicyclists actually were present, they rode closer to the road edge and motorists passed closer with less slowing or yielding AFTER SLM placement, but that reality was not described as a detriment to bicyclists.
Evaluation of Shared Lane Markings is not valid and reliable research. It is unethical junk science.
Addendum: In March 2011 MLK Jr. Blvd was resurfaced and the SLMs were placed at 24″ from the gutter pan seam, the MUTCD minimum. This was done by Town of Chapel Hill transportation staff even though they were informed by me that the placement was dangerous and UNC’s report fatally flawed. Email records also show that the SLMs were placed before Town advisory boards had given their opinions, and that my critique was not given to the BiPed Board as I had requested.