Slower Traffic Keep Right Signs | Official MUTCD R4-3

Slower Traffic Keep Right signs are essential roadway tools for maintaining smooth, predictable traffic flow on busy streets, private roads, industrial drive lanes, and commercial properties. These signs provide clear and immediate instruction to drivers in multi lane environments, reducing congestion, preventing bottlenecks, and improving overall safety where higher speed traffic needs an unobstructed left lane. Property managers, municipalities, HOAs, logistics yards, and corporate campuses rely on this sign to direct slower vehicles toward the right lane and keep traffic patterns consistent throughout the day.

Every sign in this collection is manufactured on heavy duty aluminum with engineer grade, high intensity, or diamond grade reflective sheeting for superior visibility day or night. The material will not rust, warp, fade, or peel, even under constant UV exposure and harsh weather conditions. Mounting holes are predrilled for easy installation on U channel posts, square posts, breakaway systems, and standard hardware.

Our Slower Traffic Keep Right signs meet MUTCD specifications for layout, contrast, lettering, and reflectivity, making them suitable for official use on regulated roads as well as private property. Whether you are replacing outdated signage or standardizing a full property system, these signs deliver long lasting performance and clear driver guidance.
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Highway Placement Standards (MUTCD Section 2B.30)

To effectively manage lane discipline and capacity, Slower Traffic Keep Right Signs must be installed at specific intervals:

  • Initial Placement: Install the first R4-3 sign approximately 200 to 500 feet after a new lane opens up (e.g., the start of a passing zone or climbing lane). This establishes the rule immediately as traffic spreads out.
  • Reassurance Spacing: On long stretches of multi-lane highway, repeat the sign every 3 to 5 miles to remind drivers to vacate the left lane after passing.
  • Climbing Lanes: For steep grades, place the sign at the bottom of the hill to ensure heavy trucks move right before they lose speed and block traffic.

Federal Standards for MUTCD R4-3 Slower Traffic Keep Right Signs

On multi-lane highways, the efficient movement of traffic depends entirely on lane discipline. Slower Traffic Keep Right Signs (R4-3) are the primary regulatory device used to enforce the "Keep Right" rule, ensuring that the left lane remains open for passing. Under MUTCD Section 2B.30, these signs are critical for maintaining highway capacity and reducing the dangerous practice of "left lane camping."

The R4-3 Regulatory Standard

To be legally enforceable by state troopers and highway patrols, Slower Traffic Keep Right Signs must meet specific federal criteria:

  • The Legend: The sign must feature the text "SLOWER TRAFFIC KEEP RIGHT" in black lettering on a white background. This indicates it is a Regulatory Sign (mandatory law), not a warning or suggestion.
  • The Code: R4-3 is the designated MUTCD code.
  • The Size: The minimum size for conventional roads is 24" x 30". For Freeways and Expressways, the size must increase to 36" x 48" or 48" x 60" to be readable at 65+ MPH.

Enforcing "Left Lane Laws"

Many states (including Florida, Georgia, and New Jersey) have recently strengthened laws penalizing drivers who impede traffic in the passing lane. Slower Traffic Keep Right Signs are the legal notice required to enforce these statutes.

  • Climbing Lanes: On steep highway grades, heavy trucks lose speed. Installing Slower Traffic Keep Right Signs at the beginning of the incline allows police to cite trucks that fail to move over, clearing the fast lane for passenger vehicles.
  • Passing Zones: On rural four-lane highways, these signs are installed periodically to remind drivers that the left lane is for passing only.

Reflectivity for Highway Safety

Because Slower Traffic Keep Right Signs are typically used on high-speed roads (55 MPH+), they must be highly reflective.

  • High Intensity Prismatic (Type IV): The standard specification for highway regulatory signs. It ensures the white background creates a sharp contrast with the black text under headlamp illumination.
  • Diamond Grade (Type XI): Recommended for overhead gantry mounting or areas with high ambient light (urban highways).

Frequently Asked Questions

Common questions regarding MUTCD compliance, installation standards, and material specifications for regulatory signage.
What is the difference between "Keep Right" and "Slower Traffic Keep Right"?

"Keep Right" (R4-7) features an arrow and is used to direct traffic around a physical obstruction, like a median divider or traffic island. "Slower Traffic Keep Right" (R4-3) is a behavioral regulation used on open highways to sort traffic by speed. You cannot use them interchangeably.
Where should Slower Traffic Keep Right Signs be placed?

Slower Traffic Keep Right Signs should be placed at the beginning of any multi-lane section where passing is permitted. For long stretches of highway, they act as "Reassurance Markers" and should be repeated every few miles, particularly after major on-ramps where new traffic enters the flow.
Are these signs required for passing lanes?

While not strictly mandatory in every single zone, they are highly recommended by traffic engineers to maximize road capacity. Without Slower Traffic Keep Right Signs, drivers often default to "lane squatting," which reduces the effective capacity of a 2-lane highway to a 1-lane highway, causing backups and increasing the risk of aggressive tailgating.

Need specific code assistance?

If your project requires a specific State DOT certification or a specialized variation not listed here, please contact our Compliance Support Team for a custom specification sheet.