This MUTCD interpretation letter allows the installation of tubular markers (flex posts) on the lines at crosswalks to channelize traffic. It is not an experimental device.
Interpretation Letter 3(09)-61(I) - Channelizing Devices at Mid-Block Pedestrian Crossings in Conjunction with In-Street Pedestrian Crossing (R1-6 Series) Signs
To provide additional emphasis for the pedestrian crossing and to provide a channelizing and potentially calming effect on vehicle traffic, one or more tubular markers may be used on the center line, lane lines, or edge lines at a mid-block pedestrian crossing. This use of tubular markers does not require experimental approval since it is compliant with the MUTCD. If used, the tubular markers shall be the same color as the pavement marking that they supplement, in accordance with Section 3H.01 of the MUTCD. When the tubular markers are used to supplement an R1-6 Series sign that is either on the center line, lane line, or median island, they should not be used on the same pavement marking line where the R1-6 Series sign is installed.

