School Bus: Stop Signal Arm
12 questions in the bank cover this topic. Everything below is drawn from the sources those questions cite.
Sources: 49 CFR 571.131
What you need to know
FMVSS 131 S4 defines it in terms of a signal not to pass while the bus is loading or discharging.
S2 states the standard's purpose as reducing deaths and injuries from vehicles passing a stopped school bus. The bus has stopped to load or discharge passengers.
Stop signal arm means a device that can be extended outward from the side of a school bus to provide a signal to other motorists not to pass the bus because it has stopped to load or discharge passengers.
49 CFR 571.131
FMVSS 131 S5.1 requires a regular octagon of at least 450 mm, or 17.72 inches.
The octagon matches the MUTCD's exclusive STOP shape, so its meaning is unmistakable.
The stop signal arm shall be a regular octagon which is at least 450 mm × 450 mm (17.72 inches × 17.72 inches) in diameter.
49 CFR 571.131
FMVSS 131 S5.2 requires red on both sides, with a white border and white STOP lettering added by S5.2.1 and S5.2.2.
Red is the MUTCD color for stop or prohibition.
The stop signal arm shall be red on both sides, except as provided in S5.2.1 and S5.2.2, and S5.2.3.
49 CFR 571.131
FMVSS 131 S5.2.1 requires a white border at least 12 mm, or 0.47 inches, on both sides.
Mounting hardware may obscure no more than 15 percent of the border on each side.
The stop signal arm shall have a white border at least 12 mm (0.47 inches) wide on both sides
49 CFR 571.131
FMVSS 131 S5.2.2 requires white upper-case STOP at least 150 mm, or 5.9 inches, tall with a stroke width of at least 20 mm, on both sides.
The stop signal arm shall have the word “STOP” displayed in white upper-case letters on both sides, except as provided in S5.2.3. The letters shall be at least 150 mm (5.9 inches) in height.
49 CFR 571.131
FMVSS 131 S5.2.3 keeps the forward side of the rearmost arm blank, and S5.3.1.3 keeps it unreflectorized.
A driver alongside the bus should not see two conflicting STOP faces.
When two stop signal arms are installed on a school bus, the rearmost stop signal arm shall not contain any lettering, symbols, or markings on the forward side.
49 CFR 571.131
FMVSS 131 S5.3.1.2 caps nonreflectorized hardware at 7.5 percent of total surface area per side.
A separate 15 percent allowance in S5.2.1 applies specifically to the white border.
Nonreflectorized mounting brackets, clips, bolts, or other components necessary to the mechanical or electrical operation of the stop signal arm shall not obscure more than 7.5 percent of the total surface area of either side of the stop signal arm.
49 CFR 571.131
FMVSS 131 S5.3.1 requires the entire surface of both sides in Type III material, as one of two conspicuity options.
The alternative in S5.3.2 uses red lamps instead.
the entire surface of both sides of each stop signal arm shall be reflectorized with Type III retroreflectorized material
49 CFR 571.131
FMVSS 131 S3 covers school buses but excludes multifunction school activity buses, which do not make the roadside pickups the stop arm exists to protect.
This standard applies to school buses other than multifunction school activity buses.
49 CFR 571.131
An octagon, the universal stop shape, so a driver reads it as a stop sign without having to process the lettering first.
The stop signal arm shall be a regular octagon which is at least 450 mm × 450 mm (17.72 inches × 17.72 inches) in diameter.
49 CFR 571.131
571.131 S5.2 requires all three.
Both sides matter because the arm is read by traffic approaching from in front and from behind at the same moment.
The stop signal arm shall be red on both sides
The stop signal arm shall have a white border at least 12 mm (0.47 inches) wide on both sides
The letters shall be at least 150 mm (5.9 inches) in height
49 CFR 571.131
The rear arm's forward face is blank because the only person seeing that face is you in your mirror.
Lettering there would add nothing and could confuse the view down the side of the bus.
When two stop signal arms are installed on a school bus, the rearmost stop signal arm shall not contain any lettering, symbols, or markings on the forward side.
49 CFR 571.131
Check yourself
- The defined purpose of your stop signal arm is ______.
- What shape and minimum size must your stop signal arm be?
- What color must your stop signal arm be?
- What border does your stop signal arm require?
- What lettering must appear on your stop signal arm, and how tall?
- Your bus has two stop signal arms. What applies to the rearmost one?
- How much of your stop signal arm's surface may mounting hardware obscure?
- What reflectorization does the standard require on your stop signal arm?
- Which vehicles does the standard apply to?
- What shape and size must your bus's stop signal arm be?
- What is required of your stop signal arm?
- Your bus has two stop arms. What is different about the rear one?
Answers are in the practice test for this topic.