Speed Feedback and Changeable Message Signs

DEFINITION AND DESCRIPTION

Dynamic speed feedback signs contain devices that measure the speed of an approaching vehicle and displays the speed to the vehicle operator.  They are used to provide warning to drivers of their speed in relation to either a speed limit (R2-1) sign or a horizontal alignment warning sign assembly with an advisory speed.  Sign installations can be permanent or temporary. They are often used in transitions zones that link high-speed to low-speed contexts or on approaches to curves on high-speed roadways to help prevent roadway departure crashes. Installations on two-lane rural horizontal curves are associated with CMFs of 0.93 – 0.95 (Hallmark et al., 2015).

Implementation Categories

CONSIDERATIONS

• Signs can be mounted permanently on a standard metal pole.
• Must meet applicable MUTCD requirements. See Section 2C.13 for Speed Feedback Signs and Chapter 2L for CMS. Also see Traffic Operations Guidance Manual TO-403-12 for more information.
• Often utilize self-contained power (e.g. solar).
• Requires DSHE approval through the Division of Traffic Operations (except when used in highway work zones).
• Except for installations in highway work zones, Vehicle Speed Feedback signs and plaques shall require the approval of the Deputy State Highway Engineer for Project Delivery and Preservation.

APPLICATION

• Mobile signs may be used for construction and maintenance work zones.
• Mobile or permanent signs may be placed in speed transition zones approaching communities.
• Evaluate using permanent installations at locations with a higher probability of roadway departures (e.g., long tangents before curves with significantly lower design speeds, locations with a history of roadway departures).
• Place signs based on perception-reaction time, deceleration, and expected reduction in speed so the driver has time to react and adjust their speed (see MUTCD Table 2C-3 for minimum advance placement distance). Provide a clear line of sight to signs.
• When used to display the speed of an approaching vehicle in relation to the posted speed limit, the Vehicle Speed Feedback (W13-20aP) plaque shall be mounted below a Speed Limit sign.
• When used to supplement a horizontal alignment warning sign advisory speed, the Vehicle Speed Feedback sign (W13-20) shall be an independent installation near the point of curvature of a horizontal curve.
• The changeable display should not be activated when approach speeds are less than 10 MPH below the speed limit.
• The changeable display may be set to remain blank when the speed of an approaching vehicle is greater than 20 MPH above the posted speed limit to deter drivers from attempting to make the sign display a high number.
• The changeable display showing the speed of the approaching vehicle shall be a yellow luminous legend on a black opaque background. The minimum LED numeral height should be in accordance with the Standard Highway Signs publication.

example

Image Source: MUTCD, 11^th Edition

Complimentary SSA Strategies

• Curve Widening
• Enhanced Signing