When can a W1-1a or W1-2a combining horizontal warning AND advisory speed be used?
The National MUTCD has turn and curve signs with the recommended speed on the sign itself. Many agencies have used these signs in lieu of the standard combination sign with recommended speed plaque. This is improper use! They probably should be called supplemental horizontal alignment warning signs.
These new signs are just supplemental to the standard signs and are placed at the “point of curvature” (the start of the curve). The W1-1a and W1-2a signs are installed when vehicles still need additional reminders about an alignment change. Here is the order to placing signs for a curve.
- Place appropriate advance curve warning sign (W1-1 or W2-1 with an advisory speed plaque if needed).
- Next, install chevrons or arrows to help delineate the curve. Chevrons or large arrows help guide the motorist through the curve. They are required on arterial and collector highways when the difference between the speed limit and the advisory speed is 15 mph or more. They can be placed on any curve when there is a need to help alert drivers.
- Finally (and only after trying the first two steps), place a W1-1a or W1-2a supplemental horizontal alignment warning sign. The speed in the supplemental horizontal alignment warning sign must match the advance warning signs. The sign is placed at the beginning of the curve.
Figure 2C-2 from the MUTCD illustrates the proper use of these signs.
National MUTCD Section 2C.10