Semisequicentennial Transportation Conference Proceedings
May 1996, Iowa State University, Ames, Iowa

An Innovative, Train-Illuminated Passive Warning Sign for Highway-Railroad Grade Crossings

Eugene R. Russell, Sr. and Margaret Rys

Kansas State University,
Seaton Hall,
Manhattan, Kansas 66506.

In the United States, there are approximately 170,000 public highway-railroad crossings at grade. About 65 percent of these are on low-volume roads and have no automated warning devices (passive grade crossings). Upgrading these passive crossings to automatic, train activated warning devices (active grade crossings) is not cost effective because of the low highway traffic volumes involved. These passive grade crossings on low-volume rural roads account for about one-half of the 600 annual fatalities from vehicle-train collisions at grade crossings in the U.S. (A high percentage of these occur at night.) There is need for effective, low-cost devices at these grade crossings. One such device that was evaluated by the authors was developed by the Burlington Northern Railroad Company (BN) and 3M Company (3M). This Passive Warning Sign (PWS) has no lights or electrical connections, but is designed to light up and have an "active look" as a train locomotive approaches the grade crossing. The sign is a rectangular "box" with clear side panels and a translucent front panel which can contain any message or symbol. Light from the train locomotive's headlamps strikes the side panel of the sign and is redirected and spread through the front panel by a special 3M, proprietary thin-film material. Thus, the sign appears to have internal lighting. Whatever message or symbol on the front panel is lit up and can be seen by an approaching motorist from several hundred meters. The sign takes very little light and a train's headlamps illuminate the sign from distances in excess of 650 meters. For a train traveling at 105 kph, an approaching driver has approximately 23 seconds of warning, about the same as most train activated warning systems. The sign was evaluated in many adverse environmental conditions—rain, ice, snow, blizzard, dusk, etc. It was concluded from the study that the PWS sign is effective under all these conditions when illuminated by a train's headlamps. The paper details the experimental use of the sign at two grade crossings and the study design conducted to evaluate its effectiveness. It is concluded that the PWS is effective and should be promoted for use at specific grade crossings, as recommended in the paper. Key words: highway-railroad grade crossings, passive warning sign, train-illuminated warning sign, low-cost grade crossing warning devices.

Across the United States, there are approximately 170,000 public, rail-highway crossings at grade (grade crossings) (1). These railroad crossings are commonly categorized as "active" (having train-activated warning devices) or "passive" (having no train-activated warning devices). About 65 percent of the public, grade crossings are low-volume, passive crossings. Upgrading these passive grade crossings to active status is not cost effective. However, about half of the 600 annual deaths at grade crossings in the USA, around 300 per year, occur at these low-volume, rural crossings.

There is a need for more effective, low-cost devices at these low-volume grade crossings and a renewed interest in research and development of promising devices. Burlington Northern and 3M Corporation teamed up to design a warning sign designed to give drivers on the highway approach better warning of approaching trains. The device, referred to in this paper as the Passive Warning Sign (PWS), is designed to look "active" when a train is approaching a grade crossing. Light from the train locomotive's headlamps strikes the side panel of the sign and is redirected through a front panel by a special 3M, patented, thin-film material. The redirected light rays light up the front panel so that it appears to be internally illuminated. The PWS is sensitive to very low light levels and appears to light up when a train locomotive with standard road headlamps is 609.6 m (2,000 feet) or more from the crossing.

A schematic diagram of the PWS concept is shown in Figure 1. The sign face can have any symbol or word message. The signs used in this study have the word message YIELD, vertically, in white letters on a red background. The dimensions are shown in Figure 2.

The PWS is intended to be used with the standard crossbuck sign, and not to replace it. It is designed to increase the effectiveness of the "message" given to an approaching driver, particularly at night. During the daytime, the sign and unit message are visible to approaching motorists as would be any highway sign. Likewise at night, the sign and unlit messages are visible in the headlight beam to approaching motorists. At dawn and dusk, light from the sky illuminates the sign. During and after snowstorms, the PWS is much more conspicuous than the white crossbuck, which tends to blend into the white background.

The PWS concept is that the face and message are illuminated and appear to "light up" during the approach of a train. At distances in excess of 609.6 m (2,000 ft.), light from the locomotive headlamp strikes the side panels of the PWS and the front panel is illuminated. This gives an approaching driver approximately 23 seconds warning of the approach of a train traveling at 96.6 kph (60 mph), about the same as most active signal systems with constant warning circuitry. The YIELD message reminds drivers of their responsibility at passive grade crossings.

The objective of this study was to determine the effectiveness of the PWS. The criteria used were:

  1. sign visibility distance,
  2. sign legibility distance,
  3. expert, subjective, observation and evaluation,
  4. understanding and acceptance by subjects, and
  5. adverse weather reliability and durability.

Details of the study design are contained in following sections.


To evaluate the effectiveness of the Passive Warning Signs (PWS), two series of tests were conducted using subjects to evaluate the PWS, plus two additional studies described briefly below.

In the first series, the PWS (with a crossbuck) was compared to the standard crossbuck alone. Two techniques used in the lab to do this were:

  1. Subjects evaluated day and night slides of the two sign systems with a preference test.
  2. Subjects evaluated day and night slides of the two sign systems from different distances on the approach.

In the second series of tests, two field studies were conducted:

  1. Subjects were driven over grade crossings near Springfield, Missouri, to determine their reaction to the PWS.
  2. Subjects were driven over a simulated grade crossing near Manhattan, Kansas, to substantiate the Springfield results and obtain additional information.

The first of the two additional studies involved the subjective, expert observations of the research team. The other study involved observing the durability and subjectively evaluating the effectiveness of the sign itself under severe, adverse weather conditions during four changes of seasons over the period of a full year.

Series I: Lab Studies

Technique one had subjects view two slides, simultaneously, of the two different passive grade crossing sign systems, the standard crossbuck and the PWS system with the crossbuck, photographed from four different distances (183 (600), 122 (400), 61 (200) and 30.5 (100) m (ft.)). The subjects were 40 volunteer engineering students from Kansas State University, divided into four groups of 10. Each group viewed the slides together. The slides were shown in five-second intervals.

Technique two had subjects view slides of each passive grade crossing sign system at a time from approaching distances (609.6 (2,000), 549.6 (1,800), 487.7 (1,600), 426.7 (1,400), 365.8 (1,200), 304.8 (1,000), 243.8 (800), 183 (600), 122 (400), 61 (200) and 30.5 (100) m (ft.)). Subjects were given a questionnaire that had the selected distances marked on them and were asked 1) how many signs could be seen from each distance, 2) the types of signs that were seen at each distance, and 3) the meaning of the signs seen at each distance. The slides were evaluated first using daytime slides and then using nighttime slides.

Series II: Field Studies

The objective of these studies was to use actual field conditions to evaluate the PWS. Two field studies were conducted, one at actual grade crossing sites in Springfield, Missouri, the other at a simulated crossing in Manhattan, Kansas.

When taking subjects to the field, it was inconvenient, time consuming, and costly (impossible at the simulated crossings) to have a train present during tests. It was essential, however, that 1) the KSU study team verify at least subjectively that the PWS sign was illuminated by an actual BN road unit at 609.6m (2,000 feet) as claimed, 2) determine subjectively how bright the PWS sign was with the train at different distances from the grade crossing, and 3) obtain illuminance readings on the sign at various train distances. These determinations were made with a BN locomotive at the Springfield, Missouri site. The PWS sign did clearly "light up" with the train at 609.6m (2,000 feet) from the crossing. The PWS is bright enough to be recognized as "some sort of red light" from several thousand feet. As the train approached the crossing, the sign got brighter. At 304.8m (1,000 feet) the light seemed to be optimum. At 152.4m (500 feet) the light was too bright and the YIELD message "blurred," i.e., the letters appeared to run together. In subsequent tests, the PWS was illuminated by a simulated headlight system (locomotive headlamps operated by battery) to the equivalent illumination of the locomotive at 304.8m (1,000 feet).

The first field experiment was conducted in Springfield, Missouri, Greene County. Groups of subjects were driven over four sections, two with the PWS signs, one with standard, active grade crossing warning signals and signing and one with no grade crossing.

The second experiment was performed at a simulated grade crossing on an isolated, county road in Pottawatomie County, Kansas, near Manhattan, Kansas. The PWS was viewed in two different positions on successive nights. One night it was placed on the left; the second night it was placed on the right. Twenty-eight KSU students participated on a voluntary basis in this experiment.

Results of a Springfield Experiment

Twenty-six subjects participated in this experiment. Ten subjects viewed the PWS first during the day and then during the night. The PWS was illuminated during the day and night using locomotive headlights powered from car batteries to simulate approaching train illumination from a distance of about 304.8 m (1,000 feet). The PWS was located on the left side of the road.

The mean recognition distance from which the subjects could see that there is a PWS during the day was 259.1 m (850 feet) and during the night 304.8 m (1,000 feet). The mean distance from which the subjects could read the YIELD message on the PWS during the day was 146.3 m (480 feet) and during the night 143.2 m (470 feet). During the day, the subjects had no prior knowledge of the sign. When the same group went out again at night, they had prior knowledge of the PWS acquired during the day experiment.

There is no significant difference in mean distances for either recognition or reading distance between day and night.

After the experiment, discussions were conducted with the subjects. They were asked to give their reactions, opinions, ideas, etc. regarding the effectiveness of the PWS. Most subjects were positive about the PWS concept, although some had concerns about understanding what the sign meant.

Results of Manhattan Experiment (Pottawatomie County)

It was desired to compare the sign on the left side vs. the right side. This was done at the simulated grade crossing.

Twenty-eight subjects viewed the PWS during the night in this experiment. The PWS was positioned one night on the left side of the road, and on the second night on the right side of the road.

When the illuminated PWS was positioned on the right side of the road, it was seen by the subjects from a mean distance of 451.1 m (1,480 feet). The subjects could read the YIELD message on the PWS at a mean distance of 100.6 m (330 feet). When the PWS was positioned on the left side of the road, it was seen by the subjects from a mean distance of 478.5 m (1,570 feet). The subjects could read the YIELD message on the PWS at a mean distance of 140.2 m (460 feet).

When comparing the mean reading distances of 140.2 m (460 feet), left side, and 100.6 m (330 feet), right side, the data indicated a statistically significant difference based on the position of the PWS. (The authors do not believe that there should have been this difference and suspect the data or the sign setup on the second night with the sign on the right side.) When comparing the reading distance with the sign on the left 143.2 m (470 feet) vs. 140.2 m (460 feet), there was no significant difference between subjects from Manhattan and Springfield experiments.

All the Manhattan subjects were viewing the sign and message for the first time and were not told what they were looking for. The KSU team, all very familiar with the sign, can recognize that the sign is illuminated from a mile or more away and can clearly read the YIELD at distances around 183 m (600 feet). Considering the data at both sites from both tests, and the KSU teams' observations, the distance at which the illuminated sign is noticed by the average motorist is about 457.2 m (1,500 feet) and the distance at which the message can be clearly read by the average motorist not familiar with the PWS is about 137.2 m (450 feet). These distances are within the distance necessary to take safe action at a grade crossing where speeds on the approach are 88 kph (55 mph) or less (2).

Weather/Seasonal Durability Studies

A single PWS was obtained for study and use in Manhattan. When not being used for field studies the PWS was installed on a road within the Riley County maintenance yard.

Subjectively, it was determined that the PWS sign is most effective during dusk and dawn and adverse weather conditions both in the daytime and nighttime. In the daytime, at dawn, dusk and during conditions of poor or limited ground visibility when the sky is relatively brighter than at ground level, the sign appears "lit." Snow does not stick, nor was any dust or road dirt ever noted to be a problem. When coated with ice, either on the side panels or front panels or both, neither the visibility nor the legibility of the sign was compromised.

Subjective Evaluation

The expert opinion of the principals in the study is that the PWS is an effective sign but for limited use, i.e., it probably should not be considered for general use. The conditions suggested for its effective use are covered below.


The authors believe that the concept of the PWS sign developed by Burlington Northern and 3M Corporation is excellent and should be promoted for grade crossings with the following specific conditions:

The authors believe further that the PWS could have great value as an interim sign that could be put up immediately after it has been determined there is a need to upgrade passive devices to active devices at any grade crossing. The current PWS sign has some concerns:

  1. Rail-Highway Crossing Inventory Bulletin. Federal Railroad Administration Calendar Year 1992, Issue No. 15, Washington, D.C., August 1993.
  2. Manual on Uniform Traffic Control Devices, Washington, D.C., 1988.

The research on which this paper is based was funded by the Burlington Northern Railroad (BN). The views, opinions, recommendations, and conclusion in this paper are those of the authors only.

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