Slippery When Wet Sign: W8-5 Sizes, Plaques and Placement
Updated · By the Cone to Curb editors
The slippery when wet sign is the MUTCD's W8-5: a car with two skid marks on a yellow diamond, used to warn of a surface that turns slick when wet. It's 30 x 30 inches on single-lane conventional roads, 36 x 36 on multi-lane roads and expressways, and 48 x 48 on freeways, with optional plaques such as WHEN WET, ICE or STEEL DECK that say why.
| Road | W8-5 size | Road condition plaque (W8-5P and similar) | ICE plaque (W8-5aP) |
|---|---|---|---|
| Conventional road, single lane each way | 30 x 30 | 24 x 18 | 24 x 12 |
| Conventional road, multi-lane | 36 x 36 | 24 x 18 | 24 x 12 |
| Expressway | 36 x 36 | 30 x 24 | 30 x 18 |
| Freeway | 48 x 48 | 36 x 30 | 30 x 18 |
| Minimum | 24 x 24 | (none) | (none) |
| Oversized | 48 x 48 | 36 x 30 | (none) |
Sizes in inches, from MUTCD Table 2C-1. On multi-lane conventional roads posted above 35 mph, no diamond warning sign may be smaller than 36 x 36 (Section 2C.03).
When it's the right sign
Section 2C.30 lists the W8-5 as optional, for unexpected slippery conditions: a bridge deck, a polished curve, a stretch where oil and rubber build up, a steel grate. Putting it on every road that gets wet trains drivers to ignore it. If the problem is ice on a bridge in winter, the BRIDGE ICES BEFORE ROAD (W8-13) sign says it more directly and can be covered in summer.
Plaques that say why
| Plaque | When |
|---|---|
| WHEN WET | The surface is fine dry |
| ICE | Seasonal icing |
| STEEL DECK | Grated or plate bridge decks |
| EXCESS OIL | Oil buildup, often near truck stops and intersections |
A plaque goes below the sign on the same post, and its background color matches the sign.
How far ahead
Place surface condition signs ahead of the start of the slick section, with more signs along it if it's long (2C.30). Table 2C-3 sets advance placement by speed. For a condition that needs drivers to slow down but not stop, the distance depends on the speed they need to slow to: at 40 mph slowing to 20 mph the table gives 100 feet, and at 55 mph slowing to 30 mph, 200 feet. Add at least 100 feet when a sign has small lettering or more than four words.
Mounting
At least 5 feet to the bottom of the sign in rural areas, 7 feet where people park or walk (Section 2A.15). On a curve, set it where the driver sees it before the curve starts, not in the curve.
Not the same thing: wet floor signs
A yellow A-frame "Caution: Wet Floor" sign for a lobby or store is a different product with no MUTCD code. This guide covers the road sign.
Mistakes we see
- 30-inch signs on a 45 mph four-lane road. The multi-lane minimum is 36 x 36 above 35 mph.
- The sign everywhere. Use it where the slickness is unexpected.
- A white plaque under a yellow sign. Warning plaques match the sign color.
What it costs
Ballpark U.S. prices in late 2026: $45 to $110 for a 30-inch W8-5 on aluminum with high-intensity sheeting, $70 to $160 for 36-inch, more for prismatic sheeting, and $20 to $60 per plaque.
Where to buy
Sign shops and traffic safety distributors that make MUTCD signs. Ask for the code (W8-5), the size, the sheeting type and the aluminum thickness.