What has the Federal Highway Administration said about Off-premise Electronic Message Centers?

The 1965 Highway Beautification Act established federal guidelines for off-premise signs (billboards) located within 660 feet of federal highways. When “changeable Electronic Variable Message Signs (CEVMS),” (typically called electronic message centers, or EMCs, in the sign industry), began to become more commonplace, individual states began to establish agreement (Federal/State Agreements — FSAs) with the Federal Highway Administration (FHWA). Terms like “flashing,” “Intermittent” and “moving” were used in an attempt to describe the CEVMS.

In hopes of establishing more standardized criteria, the FHWA’s Office of Real Estate Services, on July 17, 1996  “issued a memorandum to Regional Administrators to provide guidance on off-premise changeable message signs.”

The FHWA states, “The policy espoused in the July 17, 1996, memorandum was premised upon the concept that changeable messages that were fixed for a reasonable time period do not constitute a moving sign (emphasis added). If the State set a reasonable time period, the agreed-upon prohibition against moving signs is not violated. Electronic signs that have stationary messages for a reasonably fixed time merit the same considerations.”

Then, more than a decade later, on September 25, 2007, the FHWA issued a second memorandum, called “Guidance On Off-Premise Changeable Message Signs.” It begins by saying “The purpose of this memorandum is to provide guidance to Division Realty Professionals concerning off-premises changeable message signs adjacent to routes subject to requirements for effective control under the Highway Beautification Act (HBA) codified at 23 U.S.C. 131. It clarifies the application of the Federal Highway Administration (FHWA) July 17, 1996, memorandum on this subject.”

It then states, “Pursuant to 23 CFR 750.705, a State DOT is required to obtain the FHWA Division approval of any changes to its laws, regulations, and procedures (emphasis added) to implement the requirements of its outdoor advertising control program. A State DOT should request and the Division offices should provide a determination as to whether the State should allow off-premises changeable Electronic Variable Message Signs (CEVMS) adjacent to controlled routes, as required by our delegation of responsibilities under 23 CFR 750.705(j).”

It then suggest standards for the timing between messages and the dwell time for messages.

“Based upon contacts with all Divisions, we have identified certain ranges of acceptability that have been adopted in those States that do allow CEVMS that will be useful in reviewing State proposals on this topic. Available information indicates that State regulations, policy and procedures that have been approved by the Divisions to date, contain some or all of the following standards:

  • Duration of Message
    • Duration of each display is generally between 4 and 10 seconds – 8 seconds is recommended.
  • Transition Time
    • Transition between messages is generally between 1 and 4 seconds – 1-2 seconds is recommended.”

How Big Should a Sign’s Letters Be?

Signs need to be legible and readable, for both pedestrians and motorists. But the safety consideration becomes paramount for the latter. Consequently, the Federal Highway Administration (FHWA) sets minimum standards for the letters that appear on the interstate signs that say “Cincinnati” and “Second St.” and “Next Exit.” These standards are outlined in the FHWA-produced Manual of Uniform Traffic Control Devices (MUTCD). The exhaustive manual specifies the minimum size for every type of interstate/freeway sign. For example, a three-digit exit sign with a single-letter suffix, such as Exit 105A (designated as E1-5P 2E.31 in the MUTCD), must be a minimum of 156 x 30 in.! (13 x 2.5 ft.)

The formulae vary, but they’re based on four primary factors:

  • Distance to the viewer
  • The motorist’s speed
  • The angle from which the sign would be viewed
  • The time necessary to detect and read the sign

So if you know that the care is traveling at 70 MPH, and you know a motorist needs 2 seconds to read the sign (but 5.5 seconds to react/maneuver) , and you know to what degree the driver must turn his/her head to detect/read the sign, you can calculate how far the car will travel while the driver reads the sign, how far away the driver will be when he/she first needs to detect the sign, and then you can calculate how large the letters must be. (Font , upper/lower case,  day/night and the contrast between the letters and the sign’s background are also factors.)

Richard Schwab, who served as chairman of the Transportation Research Board, calculated Minimum Required Legibility Distances (MRLD). For example if a car is traveling at 55 mph, a sign must be legible from a distance of 440 ft. in order to be detectable and readable. At a traveling speed of 25 mph, the MRLD drops to 200 ft.

For highway signs, the standard is that each letter in a sign must be at least 1 in. tall for every 40-50 ft. of viewing distance. Thus, in our 55-mph example above, a sign that’s 440 ft. away would need to have individual letters at least 11 in. tall.

And, then, the overall size of the sign would need to consider the number of letters, and the appropriate percentage of background (or “negative space”), which is generally considered to be 60% of the overall size. Also, the further away the driver is from the sign, the higher the sign needs to be to be legible.

Again, per Schwab, signs on an urban freeway need to be 75 ft. tall. On roads with a 55-mph traveling speed, signs must be 50 ft. tall. But if the traffic speed is 25 mph, signs only need to be 12 ft. tall.

The Pennsylvania Transportation Institute of the Pennsylvania State University conducted 10 sign-related studies between 1996 and 2010. In terms of viewing distance and visual acuity, it has calculated Viewer Reaction Time average in simple environments for pre-sign maneuver is 8 seconds; and for post-sign maneuvers, 4 seconds. In complex or multi lane-environments, the pre-sign maneuver average advances to 10 or 11 seconds, respectively, and the post-sign maneuver average advances to 5 or 6 seconds.

This is included in a 2015 publication called the United States Sign Council Best Practice Standards for On-Premise Signs. Go to http://www.ussc.org/pdf/USSCSignStandardsJune102015FINALEDITION.pdf

In this same publication, Penn State has also calculated Viewer Reaction Distance. The distance between the viewer and the sign at the point of initial detection determines the letter height necessary for the viewer to acquire and understand the message. By converting Viewer Reaction Time to Viewer Reaction Distance, a relatively precise calculation of initial detection distance can be established.

Viewer Reaction Distance, expressed in feet, can be calculated by first converting travel speed in miles per hour (MPH) to feet per second (FPS) by using the multiplier 1.47.

FPS = (MPH) 1.47

Viewer Reaction Distance (VRD) is then calculated by multiplying feet per second by the Viewer Reaction Time (VRT).

The following is the resultant equation:

VRD = MPH x VRT x 1.47

The contrast (distinguishing between the sign’s copy and the background) is also impacted by the color combination. The optimum combination is black letters on a yellow background. The standard for federal highway signs, white copy on a green background, ranks at #8.

Legibility is also better for words in a combination of upper- and lower-case, rather than all capital letters, so this affects visual acuity as well.

Penn State has similarly calculated a Legibility Index that accounts for variations in visibility based on the combination of background and foreground colors. This is also included in the 2015 publication.

Overall, on average, Penn State has calculated that the ratio of necessary sign height to viewing distance is 1 in. for every 30 ft. Thus, if a sign must be readable from 300 ft., its letter must be at least 10 in. tall.

(Similarly, Dawn Jourdan, the associate professor and director of regional and city planning at the University of Oklahoma, in her 2014 evidence-based sign code, also uses an average formula of 1 in. in letter height for every 30-ft. distance from which the sign would be read.)

Also, Penn State has created a 10-step succession of calculations to determine appropriate sign size:

  1. Determine speed of travel (MPH) in feet per second (FPS): (MPH x 1.47).
  2. Determine Viewer Reaction Time (VRT).
  3. Determine Viewer Reaction Distance (VRT x FPS).
  4. Determine Letter Height in inches by reference to the Legibility Index (LI):  (VRD/LI).
  5. Determine Single Letter Area in square inches (square the letter height to obtain area occupied by single letter and its adjoining letterspace).
  6. Determine Single Letter Area in square feet: Single Letter Area in square inches/144.
  7. Determine Copy Area (Single Letter Area in square feet x total number of letters plus area of any symbols in square feet).
  8. Determine Negative Space Area at 60% of Copy Area (Copy Area x 1.5).
  9. Add Copy Area to Negative Space Area.
  10. Result is Area of Sign in square feet.

Do Electronic Message Centers Cause Traffic Accidents?

Subjective statements often suggest that electronic message centers (EMCs) cause traffic accidents because they are distracting. Yet, is there any empirical evidence that documents this theory?


In 1980, the Federal Highway Administration published its “Safety and Environmental Design Considerations in the Use of Commercial Electronic Variable-Message Signs” study, which was hugely inconclusive. It conducted the study to support its theory that electronic signage (with changeable messages) caused traffic accidents, but couldn’t generate supporting data.

In March 2011, the FHWA released a study entitled “Driver Visual Behavior in the Presence of Commercial Electronic Variable Message Signs (CEVMS)”, which is another name for EMCs. Two tests were each conducted in Reading, PA and Richmond, VA. It also showed no evidence that electronic billboards cause accidents, as indicated by the following:

-The presence of digital billboards did not appear to be related to a decrease in looking toward the road ahead.

-According to the National Highway Traffic Safety Administration (NHTSA), safety concerns arise when a driver’s eyes are diverted from the roadway by glances that continue for more than 2.0 seconds.

-The longest fixation to a digital billboard was 1.34 seconds, and to a standard billboard, it was 1.28 seconds, well below the accepted standard.

-When comparing the gaze at a CEVMS versus a standard billboard, the drivers in this study were generally more likely to gaze at a CEVMS than at standard billboards.

– The FHWA study adds to the knowledge base but does not “present definitive answers” to the questions investigated.

The study states: “In general, drivers devoted more glances at CEVMS than at standard billboards; however, there were no significant decreases in the proportion of time spent looking at the road ahead (i.e., eyes on the road) that could be directly attributed the CEVMS at the measured luminance and contrast levels.”

Glances away from the forward roadway of greater than 2 seconds or 1.6 seconds’ duration have been proposed as indicators of increased risk of crashes. In the current experiments, there were no long glances at billboards meeting or exceeding 1.6 seconds. The longest glance at a target billboard was less than 1.3 seconds in both studies. Glances with a duration of 1 second or greater were rare: there were 5 in Reading (0.47% of the glances to CEVMS) and 7 in Richmond (0.78% of the glances to CEVMS). All of the glances greater than 1 seconds were to CEVMS.

The full study can be viewed at https://www.fhwa.dot.gov/real_estate/oac/visual_behavior_report/review/cevms2.pdf

A shorter article about its highlights can be found at http://www.nxtbook.com/nxtbooks/STMG/sott_201403/index.php#/44

Additionally, Texas A&M specifically studied EMCs and “before” and “after” traffic-accident data in 2012. For that full story, go to https://fasi.squarespace.com/config#/pages/570bae5cd210b89ef1a6a42a|/universitiesblog

Similarly, in 2010, Tantala Associates, a consulting/engineering firm, conducted its fourth study about the relationship between traffic accidents and electronic signage on billboards. Most recently, Tantala examined eight years of law-enforcement records that documented 35,000 traffic accidents on state and local roads around Reading, PA, to determine accident rates near 26 digital billboards. For the first time, the Empirical Bayes Method predictive tool was used to determine if accidents near digital billboards are inconsistent with what is statistically predicted. The answer: Digital billboards are “safety neutral.”

In 2008, Tantala investigated more than 60,000 traffic accidents in Cuyahoga County (Cleveland) Ohio for an eight-year period, before and after EMC billboards were installed. Accidents in the county, as a whole, had decreased in the last four years. Accidents where digital billboards were visible also decreased.

In Rochester, NY, Tantala reviewed police records documenting 18,000 traffic accidents that occurred within a mile of digital billboards over a five-year period, and in Albuquerque, it reviewed police records documenting traffic accidents that occurred within a mile of 17 digital billboards over a seven-year period. The studies showed no statistical correlation between digital billboards and accidents.

The January 7, 2014 edition of The Hill, a Washington, DC newspaper, included the following:

“Drivers are not distracted by digital billboards alongside roads, according to a study conducted by the Dept. of Transportation. The study, which was released by the Federal Highway Administration (FHWA), found that drivers are not any more likely to be distracted by digital billboards than stationary signs.

‘On average, the drivers in this study devoted between 73% and 85% of their visual attention to the road ahead for both (CEVMS) and standard billboards,” the study said. “The range is consistent with earlier field-research studies. In the present study, the presence of CEVMS did not appear to be related to a decrease in looking toward the road ahead’.”