Can in-roadway lights be used to provide brightly visible guidelines for turning vehicles through an intersection, such as at a single-point urban interchange (SPUI)?
A distinction must be made between “internally illuminated raised pavement markers” (IIRPMs), which are regulated by Sections 3B.11 through 3B.14, and “in-roadway warning lights” (IRWLs), which are regulated by Sections 4N.01 and 4N.02. IIRPMs can be used to provide the same functions as retroreflective RPMs, such as supplementing normal longitudinal pavement marking lines. IIRPMs can be illuminated by incandescent, LED, or other light sources, but they must be steadily illuminated and not flashed. IIRPMs have been used in accordance with Part 3 standards to supplement dotted line extensions for turning movements through intersections or interchanges. In-roadway lights that are flashed intermittently have been determined to be IRWLs, which Chapter 4N requires to be yellow in color because they provide the same function as a traditional flashing beacon. IRWLs are limited in application by the current MUTCD to uncontrolled crosswalks. However, some jurisdictions have requested and receiv
