Truck-Mounted Arrow Board Size & Lamp Guide: Type A vs B vs C, 13/15/25/30 Lamps Explained

Q: What is the exact MUTCD minimum size for a Type C arrow board?

Per MUTCD §6L.06 Figure 6L-6: minimum 96×48 in (4,608 in²) panel area, minimum 15 elements, minimum 1-mile legibility distance. Source: mutcd.fhwa.dot.gov .

Q: Why do products have 25 or 30 lamps if the Type C minimum is only 15 elements?

MUTCD sets minimum performance thresholds. Commercial products exceed these minimums to provide redundancy — if individual LEDs degrade in the field, the display remains fully legible. Higher lamp density also improves brightness uniformity across the panel face.

Q: Can I use a Type B board on a freeway lane closure?

No. §6L.06 specifies Type C for high-speed, high-volume operations at or above 65 mph. A Type B panel on a freeway lane closure is a compliance deficiency.

Q: Does the dimming requirement apply to all arrow boards?

Yes. §6L.06 Standard states: "Arrow panel elements shall be capable of at least a 50 percent dimming from full brilliance." This applies to all Types. The dimmed mode is mandatory for nighttime operation.

Q: What is the minimum mounting height for a truck-mounted arrow board?

§6L.06 Guidance: the bottom of the panel should be at least 2.1 m (7 ft) above the roadway for trailer or ground-supported setups. For vehicle-mounted panels, the guidance is "as high as practical" — acknowledging that cab-top and bed-frame mounts may fall below 2.1 m on light-duty trucks.

Q: How do I verify a panel's type classification on delivery?

Request the test certificate showing the illuminated panel area (in²) against the MUTCD Figure 6L-6 threshold for the claimed type. Do not rely on outer frame dimensions or product labeling alone. Also confirm the element count and legibility distance test data.

June 9, 2026

Truck-Mounted Arrow Board Size & Lamp Guide

You ordered a truck-mounted arrow board. The supplier asks: Type A, B, or C? 15 lamps or 25? You need the board on-site in three days and the wrong spec triggers a non-compliance notice from the state DOT inspector.

This guide removes the guesswork. It maps each truck-mounted arrow board size to the road environment it covers using the exact numbers from MUTCD Figure 6L-6, explains why commercial products carry more lamps than the standard minimum, and shows where the compliance line falls. Equipment hire companies and fleet managers leave with a clear selection matrix.

Key Takeaways

MUTCD §6L.06 Type A sets a 48×24 in minimum panel size and 12-element minimum — suited for low-speed urban streets below 45 mph.
Type B requires a 60×30 in minimum panel and 13-element minimum — the standard for intermediate and high-speed mobile operations.
Type C requires a 96×48 in minimum panel and 15-element minimum — mandatory for high-speed, high-volume freeway lane closures.
Product lamp counts of 15, 25, and 30 exceed MUTCD minimums by design; higher element density improves legibility redundancy and reduces field failure risk for rental fleets.
Optraffic truck-mounted arrow boards ship in Type B and Type C configurations with auto-dimming LEDs that meet the §6L.06 50% nighttime dimming requirement out of the box.

MUTCD §6L.06 Minimum Specifications: The Exact Numbers

The MUTCD 11th Edition Revision 1 (December 2025) — the current binding US standard published by FHWA — classifies arrow panels by type in §6L.06 and Figure 6L-6. The authoritative source is the FHWA MUTCD 11th Edition Part 6 PDF.

The minimum specifications per Figure 6L-6 are:

Type	Minimum Panel Size	Min. Elements	Min. Legibility Distance	Road Speed Application
A	48 × 24 in (1,152 in²)	12	½ mile (~805 m)	Low-speed urban, < 45 mph
B	60 × 30 in (1,800 in²)	13	¾ mile (~1,207 m)	Intermediate / mobile, 45–65 mph
C	96 × 48 in (4,608 in²)	15	1 mile (~1,609 m)	High-speed, high-volume, ≥ 65 mph

Source: MUTCD 11th Edition Revision 1, §6L.06 and Figure 6L-6. Full PDF: mutcd.fhwa.dot.gov/pdfs/11th_Edition/mutcd11thedition.pdf

Critical note: These are minimum thresholds. A product with 15, 25, or 30 lamps exceeds the MUTCD minimum — it does not conflict with it. The compliance question is whether the product meets or exceeds the minimum, not whether it matches exactly.

Why Commercial Products Carry More Lamps Than the MUTCD Minimum

A 96×48 in Type C panel needs only 15 elements to pass the MUTCD threshold. Yet most commercial truck-mounted arrow boards at this size ship with 25 or 30 lamps. Understanding why matters for procurement decisions.

The Gap Between Minimum and Field-Reliable

MUTCD minimums define what is legally sufficient. They do not define what performs reliably after two years of rental fleet deployment.

A 15-element panel on a 96×48 in face distributes lamps across a large area. If two or three LEDs degrade or fail — common after 3,000+ operating hours — the display may still pass the minimum element count on paper while producing visible dark spots that reduce driver comprehension at distance. A 25-lamp arrow board on the same panel size provides density redundancy: the display remains fully legible even after several elements degrade.

What This Means When Choosing a Product

For rental companies standardizing a mixed fleet, Optraffic’s truck-mounted arrow boards cover Type B and Type C configurations — with auto-dimming LED modules that satisfy the §6L.06 50% nighttime dimming requirement out of the box. The included 4G remote controller allows one-operator mode switching from the cab, eliminating the need for a second crew member on live-traffic deployments. For confirmed panel dimensions and certified type classification of each configuration, refer to the Optraffic truck-mounted arrow board product page.

What the Type Classification Actually Controls

Type A: 48×24 in Minimum, 12 Elements

Type A is the correct specification for deployments on low-speed urban streets below 45 mph. It satisfies MUTCD §6L.06 for:

Urban street maintenance and utility work
Parking lot and event traffic control
Short-duration work with limited driver approach distance

Compliance boundary: A Type A panel deployed on a highway at 55 mph is a §6L.06 deficiency — not because the panel is physically small, but because it falls below the minimum legibility distance requirement (¾ mile) for intermediate-speed roads.

Type B: 60×30 in Minimum, 13 Elements

Type B covers the widest range of real-world truck-mounted arrow board deployments: arterial highways, state routes, and moving work zone operations. It satisfies §6L.06 for:

Arterial roads and state highways at 45–65 mph
Mobile operations where the truck moves with traffic flow
Bridge repair, resurfacing, and pavement marking on multi-lane roads

Most fleet managers ordering for mixed-use rental inventories standardize on a Type B-compliant panel as the workhorse unit.

Type C: 96×48 in Minimum, 15 Elements

Type C is mandatory for high-speed, high-volume work zones at or above 65 mph. The 1-mile legibility requirement — twice that of Type A — reflects the longer reaction distance needed at freeway speeds. Required for:

Freeway lane closures at 65 mph or above
TMA (Truck-Mounted Attenuator) shadow vehicle operations
High-volume arterials with restricted sight lines
Night work on unlit highways

§6L.06 also requires that arrow panel elements be capable of at least 50% dimming from full brilliance for nighttime operation. This is a Standard (mandatory), not a Guidance. Any Type C panel supplied to a DOT project must demonstrate compliant dimming capability.

Selection Matrix: Type and Lamp Count for Your Fleet

Deployment Scenario	Posted Speed	MUTCD Type Required	MUTCD Min. Elements	Recommended Product Lamps
Urban street maintenance	≤ 45 mph	Type A	12	13
Arterial / county road closure	45–55 mph	Type B	13	15
Highway work zone (stationary or mobile)	55–65 mph	Type B	13	15
Freeway lane closure	≥ 65 mph	Type C	15	25
TMA / freeway with DOT contract	≥ 65 mph	Type C	15	25–30

Rental company rule of thumb: Stock Type B (15-lamp) as your base unit — it covers the majority of hire requests. Add Type C (25-lamp) panels for freeway and DOT contract work. A fleet limited to Type A panels cannot legally service any DOT-managed highway call-out.

For a complete procurement decision framework — covering vehicle type, fold system, mounting bracket, and compliance verification — see the Truck-Mounted Arrow Board: Complete Buyer’s Guide for Fleets and Rental Companies.

Common Specification Errors That Cause Failed Inspections

Our team reviews fleet procurement orders regularly. These are the most frequent mismatches:

Confusing product lamp count with MUTCD minimum elements. A “15-lamp Type B” board exceeds the 13-element minimum — it does not create a new minimum. The compliance check is: does the panel meet or exceed the type threshold?
Measuring outer frame dimensions instead of illuminated panel area. MUTCD references the active display area. A 72×36 in outer frame with a 60×30 in display area is a Type B, not a Type C.
Deploying a Type B at 65 mph. The §6L.06 boundary for Type C is “high-speed, high-volume” — a 65 mph freeway. Type B is appropriate up to high-speed mobile operations, not stationary freeway lane closures.
Ignoring the dimming requirement on nighttime deployments. §6L.06 Standard requires ≥ 50% dimming capability for nighttime operation. Panels without auto-dimming or manual dimming fail this requirement on any night-shift DOT project.

Comparing Arrow Board Types: US vs Canadian Standards

Canadian buyers face an additional compliance layer. OTM Book 7 (Ontario MTO, April 2022) uses the same Type A/B/C classification as MUTCD and references the same dimensional thresholds. The key provincial additions are:

Solar/battery independence recommended for remote provincial highway deployments
Flash rate must be maintained across operating temperatures including −40 °C
Deployment plan must be approved by the MTO district office via a Traffic Control Plan

For both markets, the same Optraffic Type B and Type C panels satisfy the underlying dimensional and element count requirements. A full cross-jurisdiction compliance comparison is at: MUTCD §6F and OTM Book 7: Truck-Mounted Arrow Board Compliance for US and Canada.

FAQ: Truck-Mounted Arrow Board Size and Lamp Count

What is the exact MUTCD minimum size for a Type C arrow board?

Per MUTCD §6L.06 Figure 6L-6: minimum 96×48 in (4,608 in²) panel area, minimum 15 elements, minimum 1-mile legibility distance. Source: mutcd.fhwa.dot.gov.

Why do products have 25 or 30 lamps if the Type C minimum is only 15 elements?

MUTCD sets minimum performance thresholds. Commercial products exceed these minimums to provide redundancy — if individual LEDs degrade in the field, the display remains fully legible. Higher lamp density also improves brightness uniformity across the panel face.

Can I use a Type B board on a freeway lane closure?

No. §6L.06 specifies Type C for high-speed, high-volume operations at or above 65 mph. A Type B panel on a freeway lane closure is a compliance deficiency.

Does the dimming requirement apply to all arrow boards?

Yes. §6L.06 Standard states: “Arrow panel elements shall be capable of at least a 50 percent dimming from full brilliance.” This applies to all Types. The dimmed mode is mandatory for nighttime operation.

What is the minimum mounting height for a truck-mounted arrow board?

§6L.06 Guidance: the bottom of the panel should be at least 2.1 m (7 ft) above the roadway for trailer or ground-supported setups. For vehicle-mounted panels, the guidance is “as high as practical” — acknowledging that cab-top and bed-frame mounts may fall below 2.1 m on light-duty trucks.

How do I verify a panel’s type classification on delivery?

Request the test certificate showing the illuminated panel area (in²) against the MUTCD Figure 6L-6 threshold for the claimed type. Do not rely on outer frame dimensions or product labeling alone. Also confirm the element count and legibility distance test data.