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Innovative Intersection Safety Improvement Strategies and Management Practices: A Domestic Scan

Chapter 3. Traffic Control Devices for Motorists

Traffic Signals

During the scanning study, there were two signal treatments that captured the attention of the scan team; they are described below.

LED Signal Sections. In addition to being more energy efficient, LED signal sections are an average of 30 percent brighter than incandescent bulbs, and therefore are more conspicuous. Figure 9 depicts a signal head with LED sections in Michigan.

Photograph of a signal head.
Figure 9. Signal head with LED sections.

Signal Backplates. In preparation for the 2004 North American Conference on Elderly Mobility, the Michigan DOT installed a variety of backplates at signal heads in Downtown Detroit. Although no formal evaluation was done, there was interest in several concepts. Figure 10 illustrates reflectorized yellow backplates with black signal heads. Backplates, which have been used extensively in many areas of the country, serve several safety purposes: improve signal visibility during periods of glare, provide contrast against background colors, provide contrast against confusing or cluttered backgrounds, and frame signal indications to draw attention to them.

Photograph of signalized intersection where the signal heads have black signal faces and reflective yellow backplates.
Figure 10. Black signal faces with reflective yellow backplates.
(Photo courtesy of Kimberly Lariviere, Michigan DOT).

Traffic Signs

This section identifies and discusses several of the innovative signs that were identified and discussed during the scan.

Static Regulatory Signs for Traffic Signals. A wide variety of regulatory signs hung on span wires and mast arm poles were encountered. One specific example of that was the U-TURN YIELD sign, as illustrated in figure 11. The signal arrangement indicates that there are two left turn lanes on this approach to a signalized intersection. While not visible on this photo, there is a right-turn overlap for the side road approach to the left. Hence, there are times when a right turning vehicle may conflict with a U-turning vehicle from the outside (i.e., closest to the median) left turn lane. This regulatory sign clearly indicates that the driver from that left turning lane must yield to opposing traffic.

Photo of a signalized intersection with a 'U-TURN YIELD' regulatory sign displayed at the left turn signal head on an approach with dual left turn lanes.
Figure 11. "U-TURN YIELD" regulatory sign for Left turn signal head on an approach with dual Left turn lanes in south Florida.

Fiber Optic, Overhead Regulatory Signs for Traffic Signals. Another innovative signing treatment was identified at an intersection in Livingston County, Michigan. The innovative sign was a fiber optic sign with white letters on a dark (black) background indicating “NO TURN ON RED.” Since this was implemented with lead-lag phasing, it is important to understand that the opposing left is seeing a green left arrow indication at the same time that the “NO TURN ON RED” sign is displayed. Figure 12 displays a photograph of the treatment when the opposing left turn traffic receives a green left arrow signal indication. Figure 13 displays a photograph of the treatment when the opposing left turning traffic receives a red left arrow signal indication. Hence, the dynamic turn restriction greatly reduces the probability of a conflict between a vehicle that turns right on red from this approach and a left turning vehicle from the opposing approach.

Photo of a signalized intersection with an internally illuminated 'NO TURN ON RED' message displayed.
Figure 12. Dynamic regulatory sign at intersection in Michigan, with the "NO TURN ON RED" message displayed (when a left green arrow signal indication is displayed to opposing left turning traffic).

Photo of a signalized intersection with an unlit message sign displayed.
Figure 13. Dynamic regulatory sign at intersection in Michigan, with no message displayed (when a red left arrow is displayed to the opposing left turning traffic).

Another version of this type of sign is presented in figure 14, which shows two fiber optic signs mounted on a mast arm with a static one-way regulatory sign and two traffic signal heads. This treatment was found at the intersection of two one-way streets in Portland where the Portland Trolley runs. As can be seen in this figure, the fiber-optic/blank out sign to the left indicates “TRAIN” while the other sign indicates “NO TURN ON RED.” When no trolleys are present, drivers on the approach served by these traffic control devices can make a right turn on red. However, when a trolley is present and ready to move, the phase is terminated early and the sign displays “NO TURN ON RED.” The trolley actually turns right from the left lane at this intersection. Vehicles on both approaches must stop when the trolley makes the turn. Without the fiber optic signs, drivers in the right-most lane on the approach may believe that they can safely turn right. But since the trolley crosses this path, it is necessary to prohibit vehicles from turning right on red. The fiber optic signs fulfill a time-dependent motorist information need.

Photo of a signalized intersection with two illuminated signs displaying the messages 'Train' and 'No Turn on Red.'
Figure 14. Dynamic regulatory and information signs used in Portland at an intersection where a trolley line crosses.

Internally Illuminated, Overhead Regulatory Signs. Internally illuminated signs were quite common in Michigan. Figure 15 shows an illuminated case stop sign hung on a span wire on which overhead flashing beacons are also mounted. Another example is presented in figure 16. In this case, the illuminated case includes four faces that each indicate the simple message “LEFT” to indicate that the displays in the signal head below are for left turning vehicles.

Photo of a signalized intersection with an illuminated sign displaying a 'STOP' message.
Figure 15. Crosshead illuminated case "STOP" sign in Michigan.

Photo of a signalized intersection with an illuminated square case that says 'LEFT' on each side of the square to indicate that the displays in the signal head below are for left turning vehicles.
Figure 16. Overhead illuminated case "LEFT" sign in Michigan.

Activated Internally Illuminated Warning Signs. In Portland, Oregon, signs such as the one presented in figure 17, were used frequently at signal-controlled mid-block pedestrian crossings. The signs would not be illuminated until the pedestrian phase was activated. The signs would begin to flash when the pedestrian call button was pushed and remain flashing until fifteen seconds after the pedestrian phase was displayed. While it is somewhat difficult to perceive that the light is activated during the day, the illumination of the sign is quite dramatic at night.

Photo of an illuminated sign hung from a mast arm that displays the messages 'Ped Xing' to approaching traffic
Figure 17. Activated, internally illuminated "PED XING" warning sign hung from a mast arm.

Internally Illuminated Street Name Signs. Figure 18 depicts an internally illuminated street name sign. It is hung from a mast arm signal pole in Detroit prior to the North American Conference on Elderly Mobility. The letter heights are 12 inches and the font is Clearview. For the conference, a variety of letter heights and fonts were used, but research results are not available. The perception was that 12-inch Clearview was superior in readability and driver legibility.

Photo of an internally illuminated street name sign with 12 inch letters.
Figure 18. Overhead, internally illuminated street name sign with 12" letters in Clearview font
(Photo courtesy of Kimberly Lariviere, Michigan DOT).

Larger Street Name Signs. Several agencies indicated that they have programs to replace existing street name signs with larger street name signs cantilevered from signal poles or other poles. Figure 19 sharply contrasts the old style street name sign and the new one with six-inch letter height in Clearview font on high-intensity sheeting.

Photo of an intersection showing both an older street name sign (labeled OLD 5 and 3/8 inch Highway Series D Engineering Grade Sheeting) and a newer sign letters (labeled NEW 6 inch Clearview High Intensity Sheeting).
Figure 19. "OLD" and "NEW, improved" street name signs mounted on signal poles.
(Photo courtesy of Kimberly Lariviere, Michigan DOT).

Reverse-side mounting of signs at stop-controlled intersections. With respect to traffic control devices, most of the scan discussions were focused on traffic signals, without much time being devoted to stop-controlled and yield-controlled intersections.

One treatment, implemented by the Kent County Roads Commission in western Michigan, warrants some discussion. At all-way, stop controlled intersections with overhead flashing intersection beacons, Kent County placed “ALL WAY” signs on the back side of stop signs on the far corners of the intersection as presented in figure 20. While no scientific studies have been completed for this treatment, the opinion of the Kent County traffic engineer was that they are beneficial to drivers by providing a supplemental piece of information to motorists. Similarly, at two-way, stop controlled intersections with overhead flashing intersection beacons, rectangular warning signs have been placed on the back side to indicate “CROSS ROAD TRAFFIC DOES NOT STOP” in black letters on a yellow background. Figure 21 depicts this treatment, although the sign appears to be orange in color. It is important to note that Kent County’s practice is to place stop signs on both the near left side and the near right side of the road at approaches where needed for increased clearness. While relatively simple, this treatment has promising potential to improve intersection safety.

Photo of stop sign and flashing overhead lights at an all-way stop controlled intersection.')
Figure 20. Signing treatment for all-way stop controlled intersection.
(Photo provided by Tim Haagsma, Kent County Roads Commission).

Photo of a stop sign and flashing overhead lights at a two-way stop controlled intersection.
Figure 21. Signing treatment for two-way stop controlled intersection.
(Photo provided by Tim Haagsma, Kent County Roads Commission).

Several additional signing treatments, which were identified by one or more of the participating agencies, deserve brief mention. Although not considered innovative, these are considered effective treatments.

Pavement Markings

While the innovative markings that were seen during this scanning study were related to pedestrian crossings, there were some for vehicle traffic. One example followed by several agencies was the use of “cat” tracks or “puppy” tracks on the pavement through an intersection as depicted in figure 22 enhanced safety at the intersection, although no definitive supporting research could be provided. Figure 22 depicts an intersection with markings continued through the intersection on the mainline.

Other examples of markings include the following:

Photo depicts an intersection with markings continued through the intersection on the mainline..
Figure 22. Intersection in Richardson with "cat" tracks, which are also called "puppy" tracks.

Photo pavement markings with the text 'M-10' identifying destination of that lane on the interstate.
Figure 23. In-lane pavement marking message designating Michigan State Route 10 (M-10) applied in advance of an exist ramp.

Photo of a 'Look Right' message painted on the asphalt at the entrance to a crosswalk.
Figure 24. Pavement message for pedestrians at crosswalk.


In-Pavement Lighting Systems

The scan team visited District 4 of the Florida Department of Transportation to view a site that was actually the terminal of an off-ramp from an Interstate freeway. While the site was not an intersection, it was selected because there was a keen interest in high-speed approaches to intersections, like at-grade intersections on high-speed expressways. The application of the technology on high-speed approaches to isolated intersections could have positive safety benefits. For example, in-pavement lights could be installed along the edgeline and the centerline in advance of unexpected or sight-restricted, high-speed intersections so that the in-pavement lights flashed when the speed of a vehicle on the major road approach to the downstream intersection exceeded a specific threshold. The system may also be applicable to other intersections where speed on the major road is a contributing factor to crashes, especially nighttime crashes where the value of the flashing in-pavement lights is expected to be even greater. It is theoretically possible that an analogous system could also be operated so that the in-pavement lights only flash when the detected speed of a vehicle on the major road approaching the intersection exceeds the threshold and a vehicle is detected as stopped on the side road.

The ramp is located on southbound I-95 at the exit to westbound Florida State Route 84 in the Fort Lauderdale area. The ramp is north of Fort Lauderdale’s International Airport and close to several tourist attractions. The ramp is approximately one-half mile long and forms a T-intersection with westbound Florida S.R. 84. At the ramp terminus with westbound Route 84, a 10 mph advisory speed is posted for a sharp right turn. Speed measurements on the ramp indicated that the 85th percentile speed on the ramp on weekdays and on weekends is on the order of 51 to 60 mph. Crash data showed that from 1997 to 1999 and from 2001 to 2003 there were 86 crashes, with the majority being angles and right turns, and that an estimated 77 percent of these crashes were attributed to speeding. The results of the six months evaluation demonstrated that the speeding was reduced and no crashes have occurred during this period of time. Based on preliminary assessments, the system looks promising in its influence on speeds at the end of the ramp; thus, the system should enhance safety.

The concept implemented made use of in-pavement lights similar to those currently used for in-pavement crosswalks. It should be understood that the 2003 edition of the MUTCD currently limits the application of in-pavement lights to pedestrian crosswalks. The FHWA approved Florida DOT’s plan to test the system during a two-year period. For this experimental application, a series of lights were installed along the edgelines on the ramp. Photos of the actual devices from an angled downward view of the device without the lights on, from an angled downward view looking at the devices with the lights activated, from a top down view of the device with the lights activated, from the profile view looking straight on without the lights on and from a profile view looking straight on with the lights on are displayed in Figures 25a, 25b, 25c, 25d, and 25e, respectively.

Angled photo of an in-pavement device with lights activated.
Figure 25a. Angled view of device with lights not activated.
(Photo courtesy of Gilbert Soles, Florida DOT District 4).

Angled photo of an in-pavement device with lights not activated.
Figure 25b. Angled view of device with lights activated.
(Photo courtesy of Gilbert Soles, Florida DOT District 4).

Photo of a 'Top-Down' photo of an in-pavement device with lights activated. Device is about the size of the pen that has been placed next to the device in the photo to indicate scale.
Figure 25c. "Top-Down" view of device with lights activated.
(Although lights appear to be red in this picture, the actual color is yellow).

Photo of a 'front-on' photo of an in-pavement device with lights off.
Figure 25d. "Front-On" view of device without lights activated.
(Photo courtesy of Gilbert Soles, Florida DOT District 4).

Photo of a 'front-on' photo of an in-pavement device with lights activated.
Figure 25e. "Front on" view of device with lights activated.
(Photo courtesy of Gilbert Soles, Florida DOT District 4)

The devices have dimming capability so that they were brighter during daylight hours and dimmer during nighttime hours, and also included speed detection. A total of 50 devices were deployed. Figure 26 presents a view of the ramp where the devices were deployed. The lighting devices flash in a sequential manner when the detected speed of a vehicle entering the ramp was 50mph or greater. The system is operated by a controller unit that was mounted on a pole (see Figure 27) below the elevated ramp. Figure 28 depicts the contents of the controller cabinet.

Photo of an interstated ramp with in-pavement lighting installed along the paint lines.
Figure 26. View of the ramp of in-pavement lighting device.

Photo of a pole-mounted controller cabinet mounted to the side of an elevated ramp.
Figure 27. View of pole mounted controller cabinet for in-pavement speed reduction system mounted on an elevated ramp above.

Photo of the inside of a controller cabinet.
Figure 28. View of inside of the controller cabinet for Florida ramp.

The sealant along the outside of the edgeline in figure 29 presents the cable run for the in-pavement lighting devices. The speed of a vehicle entering the ramp just beyond the gore on the freeway is captured by means of an inductive loop detector, which is depicted in figure 30. Figures 31 and 32 present photographs of the system, with the in-pavement lights activated, at night and during the day, respectively. The deployment specifications used by Florida DOT are shown in Figure 33. By reducing the spacing, the decreasing strobe-like effect appears more pronounced.

of in-pavement lighting device and sealant showing sawcut for cable.
Figure 29. View of in-pavement lighting device and sealant showing sawcut for cable.

Photo of the detector loops used for speed detection near the 'beginning' ramp upstream of a sharp curve.
Figure 30. Loops used for speed detection near "beginning" ramp upstream of sharp curve.

Two photos showing the SR 84 off ramp, one showing the before (left) picture, and and the other showing the after (right) picture of LED modules.
Figure 31. Two views of SR 84 off ramp before (left) and after (right) installation of LED modules. Note: Roadway conditions before and after LED modules installation.
(Photo courtesy of Gilbert Soles, Florida DOT District 4).

Photo of a ramp at night with the in-pavement lights on.
Figure 32. View of the system at night with the in-pavement lights "on."
(Note: Photo courtesy of Gilbert Soles, Florida DOT District 4).

Photo of a ramp during daylight hours with the in-pavement lights 'on'.
Figure 33. View of the system during daylight hours with the in-pavement lights "on."
(Photo courtesy of Gilbert Soles, Florida DOT District 4).

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