Brooke R Ullman

Legibility Distances of Smaller Letters in Changeable Message Signs with Light-Emitting Diodes

This paper presents the results of a legibility study of 9-in. and 10.6-in. letters on changeable message signs (CMSs) with light-emitting diodes. The study, conducted in Dallas, Texas, consisted of 60 subjects, demographically balanced with respect to age, gender, and education. The subjects drove a test vehicle as they approached CMSs with one of the above letter heights. Study administrators recorded the distance from the sign at which the participant could correctly read a three-letter word. Data were recorded for three trials on each of the letter heights for each participant. Data were collected during daylight (sun overhead) and nighttime conditions. The 85th percentile legibility distance for the 9-in. letter height was 228 ft for daytime conditions and 114 ft for nighttime conditions. For the 10.6-in. letter height, the 85th percentile legibility distances were 324 ft for daytime conditions and 203 ft for nighttime conditions, respectively. The 85th percentile legibility distances for each letter height were used to estimate available viewing times under various approach speeds. These available viewing times dictate the units of information that can be presented on a CMS of a particular letter size.

Driver Understanding of Sequential Portable Changeable Message Signs in Work Zones

Results of a Texas Transportation Institute driving simulator study are presented. The studys focus was the ability of motorists to capture and process information on two portable changeable message signs (PCMS) used in sequence (i.e., one PCMS following another along the edge of the roadway such that each PCMS contains part of a single message). The purpose of the PCMS is to convey information about upcoming traffic situations. Results indicate the need to keep messages at or below the four-unit maximum recommended in existing guidelines. It was found that presenting five units of information on sequential PCMS resulted in low comprehension rates, below what would be acceptable for highway applications. However, by keeping the message length to four units, it appears that the use of the sequential PCMS will result in comprehension rates comparable with those obtained by presenting the same information at a single location on a large dynamic message sign. Comprehension may be enhanced by repeating one line of the message on both PCMS used in a given sequence.

Accommodating Pedestrians with Visual Impairments In and Around Work Zones

Results are presented of a Texas Transportation Institute study that assessed how work-zone information can be related to visually impaired users through audio messages. Researchers conducted a two-phase study that included both a laboratory survey and a field test of audio messages presented through motion-activated recordings in a mock work zone. A few of the key points found during this effort are as follows: (a) it is critical that an alternate-route message clearly state that the path will lead the pedestrian to the sidewalk on the opposite side of the street; (b) critical message elements for navigation of alternate routes were the initial turning or crossing instruction and the distance that pedestrians would need to continue on that path; (c) the existence of a high number of driveways can affect the ability of the visually impaired to count the number of blocks they have traveled and should be considered when alternate routes are established; (d) overload of information is still a concern, but there are specific message elements or terms that appear to have a greater adverse impact on recall (e.g., the use of distances in feet) than the typical message loading considerations; and (e) when it is important to provide warning messages about features for the visually impaired walking through or near a work area, it is critical to state clearly that the path is available (i.e., “sidewalk is open”).

Motorist Comprehension of Traffic Control Devices for Mobile Operations

In 2004, researchers conducted surveys to evaluate motorist comprehension of various mobile traffic control devices used to inform drivers about the number of vehicles in a work convoy; speed differential between the work convoy and the normal traffic stream; and passing a work convoy on two-lane, two-way roadways with improved shoulders. Four static signs were investigated to ascertain whether they inform motorists that they are approaching multiple work vehicles. Three of the signs (including the sign “Work Convoy”) had comprehension levels less than 53%. Placing the number of work vehicles on the sign (i.e., “3 Vehicle Convey”) improved the comprehension level to 79%. Various mobile speed displays were evaluated to determine if they provide information to motorists about the speed differential between the work convoy and approaching traffic. Only the “Your Speed” display (indicating speed of approaching vehicles) was understood by more than 85% of participants. In Texas, when mobile operations are conducted on the centerline of a two-lane, two-way roadway with improved shoulders, motorists are directed via a right flashing arrow panel to pass the work convoy to the right on the improved shoulder. However, under the current setup, only 66% of participants understood that they were supposed to pass the work vehicles on the right. All alternative text messages improved the comprehension rate; however, the “Pass on Shoulder” message was understood by the highest percentage of participants, at 97%.

License Plate and Telephone Numbers in Changeable Message Sign Amber Alert Messages

Studies were conducted with a driving simulator and laptop computers to determine the effects of displaying license plate and 10-digit telephone numbers in Amber (Americas Missing: Broadcast Emergency Response) alert changeable message sign messages. The first study was conducted using the Texas Transportation Institute driving environment simulator in College Station, Texas. A laboratory study was also conducted in six cities in Texas. It was found that the average reading time for Amber alert messages with a license plate number was significantly longer than for messages without a license plate number. In addition, the majority of subjects were not able to recall the entire number. A license plate number was found to be equivalent to more than three units of information. Thus a message with a license plate number exceeds current effective message design guidelines that specify a maximum of four units of information in a message and a maximum of three units of information in a message phase. Similarly, the average reading time for messages with a 10-digit telephone number is significantly longer than for messages without a telephone number. The majority of subjects were not able to recall the entire number. A telephone number was found to be equivalent to more than three units of information. A message with a 10-digit telephone number exceeds current effective message design guidelines.

Evaluation of Alternative Dates for Advance Notification on Portable Changeable Message Signs in Work Zones

Results of a laptop-based human factors study of alternative formats of presenting notice of future roadwork messages on portable changeable message signs (PCMS) in highway work zones are documented. A total of 192 participants across Texas were shown a series of different two-phase messages for a fixed period of time and asked questions by test administrators to determine comprehension and recall of the information presented in each message. Participants were also asked to indicate their preferred format for presenting such information on a PCMS. On the basis of these studies, it is recommended that messages that require the display of calendar dates for future roadwork and other traffic control activities use a message format consisting of the three-character abbreviation of the month (e.g., APR for April) in conjunction with the date. When future work activities span several days in the same month, the month needs to be noted only once in the message (i.e., APR 21–23) rather than repeating the month (i.e., APR 21-APR 23).

Field Evaluation of In-Lane Pavement Markings in Advance of Freeway Interchanges

Freeway interchanges with lane drops, double-lane exits with optional lanes, and other unusual geometries violate driver expectations and may result in late lane changes and erratic movements near the exit gore. In-lane pavement markings can reiterate the information provided on overhead signs that depict the geometry of the upcoming interchange. Researchers at the Texas Transportation Institute designed and conducted field studies at freeway interchanges to evaluate the operational impacts of route shield and directional arrow in-lane pavement markings. The addition of route shields resulted in better utilization of optional and inside exit-only lanes. In addition, motorists made lane changes farther upstream of the exit and made fewer unnecessary lane changes after the installation of the route shields. The addition of directional arrows also positively affected the lane distributions and lane change rate, but the effect on unnecessary lane changes was not as evident. Researchers concluded that the installation of in-lane pavement markings (either route shields or directional arrows) improved operations and, potentially, safety at the interchanges studied. There is evidence to suggest that a combination of route shields and directional arrows may be more beneficial to motorists than directional arrows alone.

Driver Comprehension of Messages on Truck-Mounted Changeable Message Signs During Mobile Maintenance Operations

Use of truck-mounted changeable message signs (TMCMSs) during mobile maintenance operations is desirable to provide drivers with information to better prepare them for unexpected conditions. Traditionally, temporary traffic control devices used during mobile operations have been limited to arrow boards and sometimes static warning messages mounted on a work vehicle. The use of warning signs in advance of an operation typically is not practical because of the constant movement and stop-and-go nature of the work. TMCMSs can fill an information gap for these mobile operations and provide drivers with better information about them, including actions to be expected. This paper describes the use of findings from a human factors laboratory study and basic message design principles to create a sampling of recommended messages for use on TMCMSs during mobile maintenance operations. These messages were defined by the type of work, road type, and the identified concerns to be addressed.

Guidelines for the Use of Pavement Marking Symbols at Freeway Interchanges

Pavement marking technology has advanced sufficiently to allow large multicolor symbols to be marked on the pavement. These symbols provide drivers with another source of information to help them make good navigation decisions. The objective of this research was to identify appropriate in-lane pavement marking characteristics for use near freeway interchanges. Two laptop-based surveys were conducted to evaluate driver comprehension, recognition time, and preference for different designs and applications. From the information obtained in these surveys, researchers developed the following recommendations for in-lane pavement markings near an interchange: (a) arrow and shield markings should be used in combination; (b) in simple single-lane exits (particularly traditional lane drop right exits), pavement marking symbols only need to be placed in the exit lane; (c) if in-lane pavement markings are used at complex interchanges (e.g., optional lanes, multilane exits), the markings should be applied to all lanes; (d) optional lane pavement markings should provide the same basic information as other lanes at that interchange (i.e., show both highway shields and an option arrow); (e) lane markings should not be staggered; (f) when all symbols are the same, they should be installed in a single line; and (g) the use of cardinal directions should be limited.

Evaluating Innovative Ideas in Pedestrian Signing for Temporary Traffic Control

A laboratory study of human factors was conducted to evaluate enhanced signing options that provide pedestrians in temporary traffic control areas with improved information on sidewalk closures. Researchers believed that improving the pedestrian information provided at work zones could result in better public compliance with signing. However, there were concerns that some pedestrian signing alternatives might be interpreted incorrectly by drivers as pertaining to their travel. As a result of these concerns, researchers conducted a human factors study from the perspectives of a pedestrian and a driver. The following are several key issues identified during this research: (a) none of the pedestrian signing alternatives affected driver understanding that the signs were intended only for pedestrians; (b) from the pedestrian perspective, the use of an orange background with black text for signs resulted in a higher level of participants indicating that they would react to the sign information (i.e., cross the street to a different sidewalk) without adversely affecting their comprehension of the sign meaning; (c) the action phrase “Use Other Side” was more intuitively understood by pedestrians than “Cross Here”; and (d) the inclusion of a distance reference to the closure is recommended for advance warning signs for pedestrians.