The Local Area Transportation Review (LATR) guidelines are a key reference point for traffic engineers, transportation planners, and other professionals involved in the development review process in Montgomery County, Maryland.
Updates to the LATR guidelines in June 2025 relate to the planning, evaluation, design, and construction of streetlighting and illuminance, which can be defined as “the measure of the total amount of light falling on a surface per unit area.” Lighting, of course, is an important aspect of street and transportation design projects.
Background
As defined in the June 2025 LATR updates, iIlluminance is the measure of the density of light on a surface divided by the area of the surface – this measurement provides an average illuminance over that area.
MCDOT’s Streetlight Design Requirements contains target minimum light level criteria by street type for both “Active Zones” and “Street Zones.” An Active Zone is the portion of a right-of-way that contains areas such as sidewalks, sidepaths, and separated bike lanes. A Street Zone is an area bound by curbs or pavement that provides access and mobility for motor vehicles, transit, freight, and emergency vehicles (containing all uses that are typically between the curbs or edges of pavement).
Illuminance Adequacy Guidelines
The June 2025 guidelines specify the following:
- When determining existing conditions as part of an LATR Study, applicants may either collect lighting values in the field or perform a photometric evaluation based on the existing fixtures being in a “like new” working condition.
- In the LATR Study Appendices, applicants should provide existing condition photometric plan sheets, a photometric legend with labels that identify each Active Zone, Intersection, and Segment, and a table with rows corresponding to locations in the legend. Inadequate conditions should be highlighted.
If conditions are inadequate, applicants must propose mitigation improvements to bring conditions to adequate levels. The mitigations must be identified even if they are not included in the final list of mitigations. Proposed conditions should be analyzed and highlighted in the plan and summarized on a table, with changed conditions highlighted.
Our traffic design team manages and collaborates on lighting projects with architects, civil engineers, developers, and public jurisdictions such as cities, counties, and municipalities, so please contact us if we can be of assistance.