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                        Methods and Practices for Setting Speed Limits: An Informational Report


            
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                Speed Limit Sign and Placement
Speed Limit signs must be correctly posted to ensure a speed limit is enforceable and to encourage compliance. Typical maximum Speed Limit signs are shown in Figure 3. In North America, the latest editions of the MUTCD and *Standard Highway Signs*33 should be referenced when developing signing for speed zones. The MUTCD contains Standards, Guidance, and Options for the signing, and general guidelines to follow for the design and layout of the signs are contained in *Standard Highway Signs.*The general guidelines show different standard sizes depending on the type of highway or facility where the sign is intended to be.

In general, *Standard Highway Signs*states that signs for regulatory speed zones shall be of the appropriate design—including size, text, and color.33 The MUTCD states that the speed limits shown shall be in multiples of 5 mph (8 km/h).15

Section 2A of the MUTCD discusses standardization of location, mounting height, lateral offset, orientation, posts, and mountings. Speed Limit (R2-1) signs, indicating speed limits for which posting is required by law, shall be located at the points of change from one speed limit to another. At the end of the section to which a speed limit applies, a Speed Limit sign showing the next speed limit shall be installed. Additional Speed Limit signs shall be installed beyond major intersections, downstream of egresses from major traffic generators, and at other locations where it is necessary to remind road users of the speed limit that is applicable. Speed Limit signs indicating the statutory speed limits shall be installed at entrances to the State and at jurisdictional boundaries of metropolitan areas.15 In rural areas, on two-lane highways, Washington State recommends locating Speed Limit signs at 10 to 20 mile (16 to 32 km) intervals.34

Figure 3. International Speed Limit Signs. Please see Extended Text Description below.

(*Extended Text Description:* Figure 3. International Speed Limit Signs. This figure shows three speed sign examples, from left to right: The first example shows a rectagular sign that says "Speed Limit 50" from the United States. The second example shows a rectangular sign that says "Maximum 50" from Canada. The third example shows a round sign with red outline that says "40" from Europe/Australia/United Kingdom.)

**Figure 3.**International Speed Limit Signs.



The preferred location for the beginning and ending points of speed zones is where there are definite changes in the character of the roadside development, like rural and urban boundaries. It is often desirable to begin and end a speed zone to encompass an important road intersection or driveway of a major generator like schools or residential developments. It is important to note the location of other traffic control devices in the segment and coordinate Speed Limit signs with them effectively.35

For all highways in Washington State, signs for both directions of travel should be located opposite one another at speed zone boundaries. Furthermore, signs should be installed on both sides of the traveled way on multi-lane divided highways. If existing highway features prohibit opposite installations, the signs may be installed a maximum distance of 300 feet (100 meters) apart, or offset up to 150 feet (50 meters) in either direction from the speed zone boundary. If these distance parameters cannot be met, the speed zone boundary may need to be adjusted to allow for sign installation.34

Figure 4 illustrates the typical location and frequency of signs for regulatory speed zones established by the Texas DOT. Distances shown between Speed Limit signs are minimums and may be greater, depending on the results of speed checks.19

Figure 4. Example Regulatory Speed Zone Application Showing Spacing of Signs Transitioning from Rural District to Urban District and Within the Urban District. Please see Extended Text Description below.

(*Extended Text Description:* Figure 4. Example Regulatory Speed Zone Application Showing Spacing of Signs Transitioning from Rural District to Urban District and Within the Urban District. The bottom section of the figure represents the rural district, and the top section of the figure represents the urban district. A road runs from bottom to top with decreasing speed limit signs with intervals/spacing of 0.2-0.5 miles. Starting at the bottom in the rural district, the first sign says "Speed Limit 55". The next sign moving up the figure is a yellow diamond sign with the text "Speed Limit 40" with an arrow ahead, indicating that the new speed limit ahead will be 40. 0.2-0.5 miles ahead of the yellow diamond sign is the actual speed limit sign which reads "Speed Limit 40". At this point the road transitions into an urban district. The first sign moving into the urban district, 0.2-0.5 miles from the rural district, reads "Speed Limit 35" which is repeated three times, 0.2-0.5 miles apart, followed by the final sign, which reads "Speed Limit 30".)

**Figure 4.**Example Regulatory Speed Zone Application Showing Spacing of Signs Transitioning from Rural District to Urban District and Within the Urban District. (Source: Adapted from the Texas Department of Transportation.19)



The following six States offer guidance concerning repetition of Speed Limit signs:36

**Alaska:**Intermediate Speed Limit signs should be placed at least once every two minutes of travel time on urban roads, and no more than ten minutes apart on rural roads (except on low volume rural roads where the signs may be up to 30 minutes apart).
	**Arizona:**Where the speed limit is less than 55 mph (90 km/h), the recommended maximum spacing is given by the formula S = V/6, where S is the maximum distance between Speed Limit signs in miles and V is the speed limit in miles per hour. In rural areas where the speed limit is 55 mph (90 km/h) or greater, the formula is modified to S = V/5.
	**California:**On freeways with limits of 65 or 70 mph (105 or 110 km/h), spacing is to be no more than 25 miles (37 km) apart. Where the freeway speed limit is reduced to 55 mph (90 km/h), Speed Limit signs are to be no more than 3 mi (5 km) apart. On conventional roads, the maximum spacing between Speed Limit signs is no more than 5 to 10 miles (8 to 16 km).
	**Minnesota:**Speed Limit signs are to be repeated at intervals of 60 seconds of travel at the posted speed where speed is reduced. The repetition may be less in dense urban areas. The maximum spacing between Speed Limit signs in rural areas is 10 miles (16 km).
	**New York:**Where a roadway speed limit is restricted relative to the State speed limit, a second Speed Limit sign is placed within 1100 ft (336 m) of the first. Subsequent Speed Limit signs are to be no further apart than 100 times the posted speed limit (e.g., for a restricted speed of 35 mph (60 km/h) the maximum separation is 3500 ft (1068 m)).
	**Pennsylvania:**Where special speed limits are in effect, the spacing between Speed Limit signs must be no more than 0.5 miles.International practices include:36

**United Kingdom and Ireland:**Place Speed Limit signs at approximately half-mile intervals where speed is restricted to less than the national speed limit for that class of road.
	**British Columbia, Canada:**On long, uninterrupted sections of rural highways, it is recommended that Speed Limit signs be repeated at least every 9 to 12 miles (15 to 20 km). Additionally, a repeater Speed Limit sign should be placed 1000 to 2000 ft (300 to 600 m) downstream of wherever the speed limit changes.**Speed Feedback Signs**

A Speed Feedback sign (also called a driver feedback sign, or variable message sign) is an interactive sign, generally constructed of a series of light emitting diodes (LEDs), that displays actual vehicle speed to drivers as they approach the sign (see Figure 5). The purpose of this sign is to reduce vehicle speeds by making drivers aware of their speed relative to the posted speed limit.30 Studies have found that Speed Feedback signs can be effective in reducing mean and 85th percentile speeds in a variety of situations.

Figure 5. Speed Feedback Sign. Please see Extended Text Description below.

(*Extended Text Description:* Figure 5. Speed Feedback Sign. Photo of a speed limit sign that reads "Speed Limit 25" on top of a speed feedback sign which reads "Your Speed 27". Behind the signs can be seen trees and a blue sky.)

**Figure 5.**Speed Feedback Sign. (Source: Richard Drdul)



If used, the changeable message sign legend should be "YOUR SPEED XX MPH" or similar wording. The legend should be yellow on a black background or the reverse of these colors. Installation of a Speed Feedback sign is optional, but if used it should be installed in conjunction with a Speed Limit sign.15

Speed Feedback signs are particularly useful at speed reductions where drivers have been traveling for some time at a higher speed. The phenomenon known as "speed adaptation" causes drivers to underestimate their actual operating speeds in these instances, and the Speed Feedback sign can assist them in achieving the necessary speed reduction.

Speed Feedback signs may be permanent or temporary installations. However, permanent installations are usually restricted to selected locations since a proliferation of Speed Feedback signs could lessen the effectiveness of the signs when they are needed most.

Speed Feedback signs typically operate as follows:

A blank display is shown when no vehicles are approaching the sign.
	An approaching vehicle's speed is displayed as a solid numeral (non-flashing numeral) if the approach speed is at or below the posted speed limit.
	The approach speed is shown as a flashing numeral if the approach speed exceeds the posted speed limit by 3 mph (5 km/h) or more.
	To discourage racing, the sign must be programmed to not display speeds that are well in excess of the posted speed limit. In these instances, the sign is most often blank. The maximum speed that a Driver Feedback sign may display is outlined in the table below:**Table 8. Maximum Speeds to Trigger a Speed Feedback Sign**

Posted Speed Limit, mph (km/h)
			Maximum Speed Display Threshold, mph (km/h)20 (30) or less
			30 (50)25 (40)
			35 (60)30 (50)
			50 (80)35 (60)
			55 (90)45 (70)
			70 (110)50 (80)
			75 (120)55 (90) or more
			80 (130)Source: Alberta Transportation37

Speed Feedback signs are most effective when combined with enforcement activities.
      
  Book traversal links for Speed Limit Sign and Placement
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                Book:Methods and Practices for Setting Speed Limits: An Informational Report
              Background
                Purpose & Scope
                Report Organization
                The Safety of Speed
                Speed Limit Basics
                Speed Limit Sign and Placement
                Speed Study Data Collection
                Speed Limit Enforcement
                Case Studies
                Summary of Results
                References
                Appendix A: Glossary
                Appendix B: Example Traffic Control Order
                Appendix C: Illinois Policy on Setting Speed Limits
                Appendix D: Northwestern Speed Zoning Technique
                Appendix E: Speed Limits New Zealand (Road Risk Methodology) U.S. DEPARTMENT OF TRANSPORTATION

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