Almost everyone has driven past one: a sign that flashes your own speed back at you as you approach. You probably eased off the gas without thinking about it. That small, automatic correction is the entire point of a radar speed sign, and it is why schools, neighborhoods, parking facilities, parks, and municipalities keep buying them.

This guide covers what these signs are, the behavioral research behind them, the recent changes to the federal rulebook that now govern how they are named and displayed, where they make the most sense, and what to confirm before you purchase. It is written for the person conducting research before making a decision.

What is a radar speed sign?

A radar speed sign, also called a driver feedback sign or your-speed sign, detects the speed of an approaching vehicle and displays that number back to the driver in real time. The driver sees their actual speed next to the posted limit and tends to self-correct. There is no ticket, no officer, and no enforcement involved, which is exactly why these signs are widely accepted by the public in a way that automated enforcement often is not.

The effect relies on a well-documented quirk of human behavior. When people are shown objective feedback about what they are doing, most adjust toward what they know they are supposed to be doing. A radar speed sign turns that into a continuous, automatic nudge at the exact spot where speeding is a problem.

Do radar speed signs work?

The short answer is that they reliably reduce approach speeds at their locations. The Federal Highway Administration recognizes speed feedback signs as a tool for managing speeds, and field experience across thousands of installations consistently shows drivers slowing in the zone covered by the sign.

A few honest caveats are worth stating, because they shape where you place a sign rather than whether you buy one. The strongest, most consistent effect is local to the sign itself, so placement matters: you put the sign where the speeding actually happens. Effects can also moderate somewhat over very long periods at a fixed location, which is one reason some agencies choose portable units they can rotate between sites to keep the feedback fresh. None of this undercuts the core case; it just means a radar-speed sign is a targeted tool, and its value comes from putting it in the right place.

The MUTCD 11th Edition changed the rules: meet the W13-20

If you bought radar speed signs a few years ago, the standards you bought them under have since been tightened and clarified. The 11th Edition of the Manual on Uniform Traffic Control Devices, the federal standard for traffic control devices on public roads, took effect in January 2024, giving radar speed signs a formal identity and a set of firm rules.

Under the 11th Edition, the radar speed sign is officially the Vehicle Speed Feedback Sign, designated W13-20, with a smaller plaque version designated W13-20aP, governed by Section 2C.13. It is classified as a warning device, not a regulatory or enforcement device. A few provisions have real consequences for what you can buy and how you can use it:

• The sign must remain blank when no vehicle is approaching. It only displays a speed when there is a vehicle to display it for.
• The display cannot flash, strobe, change color, or use animated effects integrated into the speed legend. If a product markets flashing or color-changing speed numbers, that behavior conflicts with the standard and should be confirmed with your state DOT before purchase.
• Sizing is now driven by road classification, such as single-lane, multi-lane, expressway, or freeway, and by whether the sign stands alone (W13-20) or supplements a Speed Limit (R2-1) sign as a plaque (W13-20aP). This is a shift away from sizing based purely on the posted speed limit.
• A sign can be larger than the minimum for its road class, but never smaller.
• School zones, where slowing traffic during arrival and dismissal is a constant priority. A speed feedback plaque (W13-20aP) can be mounted with a School Speed Limit assembly.
• Residential streets and neighborhoods, where cut-through speeding is a frequent complaint and where homeowners associations and small municipalities want a visible, non-confrontational response.
• Parks, trails, and campus roads, where pedestrian and vehicle traffic mix and where a calm, automatic speed reminder fits the setting.
• Parking lots and private facilities, where there is no posted enforcement but real safety risk, and where a speed sign is one of the few effective tools available.
• Is the sign built to MUTCD 11th Edition (Section 2C.13) requirements, including the blank-when-idle and no-flashing-display rules?
• Is it correctly classified and sized for your road type, and do you need the standalone sign (W13-20) or the plaque version (W13-20aP) paired with a speed limit sign?
• Does solar make sense at the site, given distance to power?
• Would a portable unit you can rotate serve you better than a single fixed install?
• Have you confirmed your state's currently adopted standard with your state DOT?
• Are you comparing total installed cost, not just the price of the hardware?

There is also a deadline that matters for procurement timing. States were required to adopt the 11th Edition or publish a compliant state supplement by January 18, 2026. For agencies that rely on federal funding, buying signs that already meet the new standard avoids the risk of installing equipment that has to be reworked or replaced. As always, confirm your state's currently adopted standard before you finalize a specification, since states can issue their own supplements.

Source: MUTCD 11th Edition, Section 2C.13 (FHWA)

A warning device, not an enforcement device

This distinction trips up many buyers, so it is worth being explicit. A radar speed sign is a warning device. It influences behavior by showing drivers their speed; it does not and cannot issue citations. Even when a sign is paired with a camera on the same pole, the speed display itself is not enforcement, and the camera is a legally separate system with its own authorization requirements that vary widely by jurisdiction.

For most buyers this is good news, not a limitation. The sign's non-enforcement is precisely why it generates so little public pushback. You are reminding people, not penalizing them, and the data shows the reminder is usually enough.

Where radar speed signs make the most sense

Because they are flexible and do not require enforcement infrastructure, radar speed signs fit a wide range of buyers and settings:

Across all of these, the buying decision is less about whether the sign works and more about matching the model, mounting, and power option to the site.

Solar, portable, and total cost

Two product choices drive most of the conversation about cost and flexibility. The first is power. Solar-powered units generate and store their own electricity, avoiding trenching and electrical permitting and making installation far simpler at sites away from existing power. For many neighborhood, park, and campus locations, solar is the practical default.

The second is whether the unit is fixed or portable. Portable and trailer- or pole-transferable units let a single sign serve multiple locations on a rotating schedule. That rotation does double duty: it spreads one purchase across several problem spots, and it helps keep the feedback effect fresh by varying where drivers encounter the sign.

As with any infrastructure purchase, compare total installed cost rather than the hardware price alone. The right comparison includes mounting, power, any site work, and whether one portable unit can cover what would otherwise require several fixed installations.

A short checklist before you buy

If you are close to a decision, work through these questions for any sign you are seriously considering:

This article is general information for procurement planning and is not engineering advice. A radar speed sign is a warning device and is not an enforcement tool. Always confirm device requirements and your state's currently adopted standard with your state DOT before finalizing a specification.