Two for the Price of One

In the National MUTCD, the W1-10 sign is available to combine an intersection and curve sign. See Figure 2 for examples. This allows a single sign to be placed when two used to be required. In addition, the single sign may be easier for the drivers to understand.

Here is an actual example to illustrate the application. Figure 1 shows a major road that curves to the left while a minor goes straight. Below the photo is a table illustrating three choices of possible signs to alert the driver of the curve and intersection.

Major road turning to the left with a
Figure 1: Major road turning to the left with a minor road going straight

Possible Signs to be Placed for the Curve and Intersection Shown in Figure 1
Signs to be Placed Notes
Old configuration for Curve and Intersection signs
This is the configuration that would have been specified in the old State MUTCD. It is confusing because there really is no road angling off to the right. The use of a sign depicting an intersecting road angling to the left would be incorrect because it would imply that the major road proceeds straight ahead.
Y intersection sign configuration
Although a Y-intersection sign might make some sense, it is not really correct either. The Y-intersection sign should only be used when there are equal traffic volumes on both legs of the Y and neither is the predominantly major road.
Single sign configuration indicating a major road curves while a minor road continues straight
This single sign provides clear information to the driver. It shows that the road turns and is also part of an intersection. You can even make the width of the minor road line slightly narrower to emphasize that the minor road is of lower volume. The sign is also bigger than the older signs, as shown in the graphic at left (not shown to exact relative scale). The minimum size of the W1-10 sign is 36 x 36 inches.

To establish the advance posting distance for the W1-10 sign, determine the advance posting distance based upon both the intersection and the curve advanced posting. The intersection advance posting distance assumes that a vehicle may have to slow to a deceleration speed of 0 mph (come to a stop) and is based upon the distance to the near edge of the intersecting roadway. The curve advance posting distance is based upon the advisory speed around the corner and is specified from the beginning of the curve. The sign should be placed at the first location that would be passed by a vehicle approaching the intersection.

Only single curves (W1-1 or W1-2) should be marked using this new sign. At most, two intersecting roads may be indicated. This includes a cross intersection or two intersections on the same side of the highway. The minimum size of the sign is 36 by 36 inches. If the sign appears to be confusing, place separate signs for the intersection and the curve. As mentioned in the table, the width of the line indicating the intersecting road may be narrowed slightly to represent the relative traffic volume.

3 additional configurations of the W1-10 sign
Figure 2: W1-10 sign (additional configurations are possible)

To illustrate the posting distances, look at the northbound lane in the aerial picture (Figure 3). The picture shows the two advance posting distances (intersection and curve) added to and plotted approximately on the figure. The location of the beginning of the curve is critical to placing the W1-10 sign. If the figure is correct, the curve distance is the critical distance for posting, since that posting distance would be the first one passed by a car approaching the intersection. The actual distances need to be checked and laid out in the field. In this case, the posted speed was used as it is allowed in the MUTCD, but in actual application you may want to investigate the prevailing speed since it is likely to be much faster.

The MUTCD allows only one W1-10 sign to be placed when two signs would have been used in the past. One sign actually may be easier to understand. Additionally, although the minimum size is larger than the old standard, a single W1-10 sign is still much less expensive than two smaller signs.

Aerial photograph of a Major road turning to the right with a minor road to the left
Figure 3: Major road turning to the right with a minor road to the left
( Image courtesy of maps.live.com )

Summer 2008

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This work by the Cornell Local Roads Program (CLRP) is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.