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B&O Color Position Light bracket masts at Magnolia, WV
North American railroad signals generally fall into the category of multi-headed electrically lit units displaying Speed based or weak route signaling.1 Signals may be of the searchlight, colour light, position light or colour position light type each displaying a variety of aspects which inform the locomotive engineer of track conditions so that he/she may keep their train under control and able to stop short of any obstruction or dangerous condition.
There is no national standard or system for railroad signaling in North America. Individual railroad corporations are free to devise their own signaling systems as long as they uphold some basic regulated safety requirements. Due to the wave of mergers that have occurred since the 1960s it is not uncommon to see a single railroad operating many different types of signaling inherited from predecessor railroads. These can be simple differences of hardware to completely different rules and aspects. While there has been some recent standardization within railroads in terms of hardware and rules, diversity remains the norm.
This article will explain some of the aspects typically found in North American railroad signaling. For a more technical look at how signals actually work, read North American railway signaling.
Contents |
Signaling aspect systems
There are two main types of signaling aspect systems found in North America, Speed Signaling and Weak Route Signaling.2 Speed signaling transmits information regarding how fast the train must be going in the upcoming segment of track, weak route signaling transmits information related to the route a train will be taking through a junction and it is incumbent upon the Engineer to govern the train's speed accordingly. Weak Route signaling is applied with the term "Weak" because some speed signal aspects may be used in the system and also because exact route information is not typically conveyed, only the fact of a diverging or straight route, each having a predictable range of known speeds.
Typically railroads in the Eastern part of the United States ran speed signaling while railroads in the west used route signaling, with some mixing of systems in the Midwest and South. This was due to the lower train density in the west combined with generally simpler track layouts. Over time, the route signaling railroads have incorporated segments of speed signaling through merger and have also adopted more speed based aspects into their systems. Of the four major Class 1 railroads in the United States, CSX uses speed signaling, Union Pacific and BNSF use speed enhanced route signaling and Norfolk Southern uses a mix of speed and route signaling based on the original owner of the line. Commuter railroads and Amtrak all use speed signaling where they own or maintain the tracks they run on. Canadian railroads all use a strong system of speed signaling in Canada, but have some segments of route signaling on lines they have acquired in the United States.
Common signaling practices
Signal types
North American signals are commonly of three types.
- Absolute - Absolute signals are usually connected to an interlocking controlled by a block operator or train dispatcher. Their most restrictive aspect is STOP and trains cannot pass them at Stop unless they obtain special authority. Absolute signals will default to displaying Stop unless expressly cleared by a control authority.
- Automatic - Automatic signals are governed by logic connected the track circuits which detect the presence of trains or obstructions automatically. Automatic signals are permissive with their most restrictive aspect being one of the Restricted Proceed variety. Trains can pass an automatic signal displaying Restricted Proceed without any outside permission. Automatic signals are typically recognized by having an attached number plate and in older practice, having multiple signal heads offset from each other on the mast.
- Semi-Automatic - Semi-Automatic signals are those that typically act as an automatic signal, but can be set to display an absolute Stop aspect. Semi-Automatic signals do not have a number plate, but can display an explicit Restricted Proceed type signal.
Other types of signals can include Train Order signals, manual block signals or signals governing special safety appliances such as slide fences, non-interlocked sidings, road crossings, etc. These are much less common than the three standard types.
Layout
North American signals generally follow a common layout. A high signal consists of one to three heads mounted roughly in a vertical stack, each head capable of displaying one to four different aspects. Automatic signals are identified with a number plate whereas absolute signals are not. The signal's aspect is based on a combination of the aspects each individual head displays. Where a signal has multiple heads, aspects are read from top to bottom and are described as "X over Y over Z".
Dwarf signals are smaller signals used in low speed or restricted clearance areas. Most signaling aspect systems have a parallel set of aspects for use with dwarf signals that differ from aspects used in high signals. Dwarf signals may have multiple heads just like a high signal, but sometimes dwarf signals use so called "virtual heads" to save on space and cost. This is where a dwarf signal displays multiple lamps on what would ordinarily be a single signal head creating the effect of multiple signal heads. For example, a stack of dwarf lamps in the order Yellow/Red/Green can display plain Yellow, Red and Green as well as Yellow over Green and Red over Green.
Behind the signal head is placed a dark backing or target, which helps improve signal visibility in bright ambient lighting. Target designs vary, but are usually round or oval, depending on the layout of the signal lamps. For each type of signal there are usually a range of target dimensions that can be chosen by the individual railroad company. As dwarf signals are not designed to be seen from long distances they are not generally equipped with targets.
Mounting
Signals are most commonly mounted on trackside masts about 12-15 feet high to put them in the eyeline of the engineer. Signals can also be mounted on signal bridges or cantilever masts spanning multiple tracks. Signals bridges and masts typically provide at least 20 feet of clearance over the top of the rail. Bracket masts are where multiple signals are mounted on the same masts governing two adjacent tracks. Bracket masts tend to be the tallest type of signal to allow the train crew to see the signal over a train on the intervening track. Signals in electrified territory may be mounted on the catenary structure and signals on bi-directional lines may be mounted back to back on the same mounting device.
Up through the 1970s signals were commonly mounted to the right of the track they governed. This was to allow the engineer to view the signal when driving a steam or diesel locomotive with a long nose that restricted the view to the left. Where bi-directional running was implemented, signals needed to be mounted above the track or on bracket masts to allow this right hand placement. As locomotive design changed to allow good visibility on both sides of the track railroads shifted to bi-directional mast type signals, using signal bridges only in special situations involving multiple tracks or restricted views.
Dwarf signals are typically mounted on the ground in areas of low speed movements of restricted clearances. Dwarf signals may be sometimes mounted higher up on a small mast or other structure for improved visibility. These can be known as "high dwarfs" or "stick signals", but a tall mounting does not change the lower speed aspects of the dwarf signal.
Signal colors and lamps
Electric signal lamps are typically low wattage (15-20) incandescent lamps running off of low voltage DC current or, more recently, high intensity LED arrays. Incandescent signals use a high power Fresnel lens to directionally focus their small power out over a long distance (over a mile on clear nights). New LED signals may either use an unfocused array or act as a drop in replacement behind a traditional lens. Signal lamps range in diameter from 3 inches to 5 inches at the outer covering.
North American signals use a standard set of colors common to other modes of transportation.
- Green - Used to indicate "clear" track conditions.
- Yellow - Used to warn the engineer of an impending stop or speed reduction. Also used for low speed movements.
- Red - Used to indicate a full stop or other restrictive condition or used as a "placeholder" light.
- Lunar White - Blue filtered light used to indicate a restricted proceed condition.
- Amber - Used in position light systems as an all-purpose high visibility color.
- (Plain) White - Plain incandescent white light. Used in some position light systems.
Individual signal heads may be set to flash a color to create a different signal aspect. Signals in the United States typically flash only one head at a time, while signals in Canada may flash two heads at a time.
Speeds
Signal rules and aspects make use of several pre-defined speeds. These speeds are also used in Weak Route type signaling.
- Normal Speed - The normal speed for the railroad line, also known as Maximum Authorized Speed (MAS).
- Limited Speed - A speed less than Normal Speed that was employed starting in the 1940s for use with higher speed turnouts. This speed is defined by individual Railroads and ranges anywhere from 40 mph to 60 mph.
- Medium Speed - This speed has a regulatory definition of being no greater than 30 mph and is used as the typical speed for diverging movements through interlockings. It is also the speed trains are limited to when approaching a Stop or Restricted Proceed type signal.
- Slow Speed - Typically 15 mph and used for trains negotiating complex trackwork at interlockings.
- Restricted Speed - Used for trains entering or operating in unsignaled territory or when entering an de-energized track circuit. Regulatory definition of no greater than 20 mph outside interlocking limits, 15 mph within interlocking limits. Trains operating at restricted speed must by able to stop within half vision short of any obstruction and must look out for broken rails.
Fault tolerance
Signals aspects are designed to incorporate some degree of fault tolerance. Aspects are often designed so that a faulty or obscured lamp will cause the resulting aspect to be more restrictive than the intended one. Operating rules require that dark or obscured signal heads be treated as displaying their most restrictive aspect (i.e. red), but fault tolerant aspect design can help the engineer take a safer course of action before the failure of a signal becomes apparent. While not all aspects are fault tolerant, the green lamp on the topmost head is only used by the least restrictive signal aspect, CLEAR, so there is no case where a failure could accidentally display a clear signal.
Where an signal aspect incorporates a flashing lamp, the flashing lamp is always applied to less restrictive signals. This is to prevent a stuck flashing relay from accidentally upgrading the signal.
Some signaling logic incorporates bulb out or other fault detection to attempt to display the most restrictive aspect in case of a fault however this is not required or universal.
Signal types
Searchlight
Searchlight signals have a common lens assembly for multiple color aspects. Original searchlight signals used a moving assembly to rotate a colored filter in front of a light source, but today several solid state searchlight signals are now on the market. Searchlight signals were invented by the Hall Signal Corporation as an updated electrical version of the older clockwork banjo signal. Hall was bought out by the Union Switch and Signal (US&S) company which still markets its "H-Series" searchlights as of 2008. The General Railway Signal (GRS) company developed its own model SA searchlight and these became the most popular type of signal in North America from the 1940's up through the 1980's.
The original electromechanical searchlight signals consisted of a low wattage incandescent bulb mounted behind a rotating armature that could hold up to 3 colored filters. In front of the filters a powerful lens focused the weak light so that within a narrow viewing angle the light could be visible for a mile or more. The design was failsafe in that a current from the track circuit logic was required to hold the armature in one of the two non-red positions. If the track circuit or signaling logic was de-energized the armature would move under force of gravity to the red position.
Searchlights became popular because the low power bulb worked well in low voltage/battery powered signal systems and also had a much longer life reducing the need for replacements in back country locations. As the efficiency of light bulbs and availability of electrical power improved the cost of maintaining and inspecting the moving electromechanical components of the classic searchlight made it less competitive with color light signals.
To overcome the issues of moving parts new solid state searchlight signals have been developed. The first, marketed as the Unilens by Safetran Systems uses fiber optics to concentrate the output of up to 4 light sources behind a single lens. More recently LED arrays with multiple sets of different color LEDs have been used to bring the searchlight concept into the 21st century.
Searchlight signals are typically mounted in a large circular target, with some railroads, like the New York Central, preferring a small target. Searchlight units may be mounted alone or on top of each other creating miniature stacks of signal heads for dwarf of close clearance applications.
Target color light
Target type color light signals consist of a cluster of three color lamp sockets in the middle of a large circular target. They were one of the first widely used type of high intensity color light signal notably adopted by the New York Central and Seaboard Coast Line railroads and later used exclusively by Conrail and New Jersey Transit.
The original GRS design made used of a cast iron box containing three high intensity lamps in a triangular arrangement. The US&S design used three smaller connected single lamp housings with a common backplate. This design was later updated to a single unit akin to the GRS model. As modular color light signals have become widespread Target type configurations have been typically offered along side "traffic light" type configurations. The target color light was made possible by increased light bulb life and efficiency as well as the greater availability of power to produce a light intense enough to be seen under normal conditions without the use of a powerful searchlight style focusing lens. This type of signal became popular in the 1930's, but was always a minority type compared with searchlights and, more recently, vertical color lights. Today, a few of these are used by the UP.
A special type of target color light called the G-Head was adopted by the Seaboard Coast Line and consisted of a standard US&S core surrounded by an oversize 4 foot diameter target backing. The notoriety of this type of signal has led many to apply the G-Head name to any signal of the target color light variety.
Vertical color light
Vertical color light signals, also known as traffic light signals, due to their similarity to the automotive signaling device, are the second major pattern of color light signals and today represent the most popular form of signal in North America, supplanting the searchlight. These signals are no different than the Target type color signal in function, but present a much altered visual appearance.
Initial problems with reliable high intensity light sources caused the first use of color light signals to occur in tunnels and other underground complexes. The 1911 New York Penn Station project was a pioneering use of combined color light signals with some examples surviving in service as of 2008. The early years of this style signal saw a large number of different design patterns which eventually condenced into two main types, the combined light, where 2 or more lamps were contained within a single cast housing, and the modular light, where each lamp was an independent unit able to be arranged into a signal of arbitrary size. The most popular combined type signal was the US&S Model N, which was available in a 2 and 3 lamp variety. The small size of the shade hoods required a rather large oval target backing which somewhat reduced the popularity compared with the more compact searchlight. Signals like the model N could also be mounted directly on the ground as a drawf signal without a backing The most notable user of this type of signal was the Chesapeake and Ohio, but units could be found on most railroads all over the country.
The current standard in North American signaling is the modular color light signal. These differ from previous types of color light signals by being composed of independent lamp modules that can be assembled into complete signal heads of arbitrary size. Early adopters of signals of this type included the Southern Railroad and the most popular models were made by GRS. The GRS units also differed from the US&S combined model by requiring a much smaller backing plate. Today the most popular type of new signal in North America is a modular design manufactured by Safetran Systems with all of the four major Class 1 railroads having switched to their almost exclusive use. Both GRS and Safetran both market separate modular systems for high signals and dwarf signals. The US&S modular system is adapted for both high and dwarf applications.
Modular color lights allow for all the cost savings inherent in color lights, but also make it easier for railroads to stock signals and perform alterations to interlockings. Instead of having to order custom heads, new modules can be taken from stock to build new signals or modify existing heads.
Another ubiquitous feature of modern modular color light signals is the full length sun shade to improve visibility in bright sunny conditions without the need for a large backing plate. Due to the appearance of the shade, signals of this type have been given the nickname Darth Vader by rail enthusiasts.
Position light
Position light signals are those which replace standard color light colors with rows of multiple lamps. The position lamps may be uniform in color or use multiple colors to further emphasize the aspect of the head. Position lights were first employed by the Pennsylvania Railroad in 1915 as a replacement for semaphore signals on the Main Line between Paoli and Philadelphia due to visibility problems caused by the new overhead electrification project. The original system used asymmetric rows of 4 lights mimicking the positions of an upper quadrant semaphore, later the system was simplified to use rows of 3 lamps, pivoting around a common center. A brilliant amber color was chosen as it was determined to have the highest visibility in smoky or adverse weather conditions. The original installation made use of lamps positioned in front of a separate black metal backing, but shortly after the lamps were embedded directly into the backing.3
A standard high position light consists of two heads, the bottom head can remain dark unless it is needed. In addition to the high position light signals the PRR developed a dwarf position light, referred to as a "pot", with 4 plain white lamps able to display 4 low-speed aspects each with two lamps. In 1930, close clearances of the Suburban Station complex spurred development of the pedestal type position, which consisted of two position dwarf signals in a common cast backing.
PRR type position lights were used throughout the vast Pennsylvania Railroad system as well as the Long Island Rail Road, a PRR subsidiary, and the Norfolk and Western, 1/3 owned by the PRR. Union Switch and Signal was the sole supplier of classic position light equipment.
In 1954 the PRR experimented installing red lenses in the horizontal position of the upper head to help increase the recognizably of absolute Stop signals at Overbrook interlocking.4 Under the Penn Central and later Conrail it became standard practice to add these red lenses to high position lights and even some pedestal signals. The Norfolk and Western modified its signals to use Red and Green lenses in the upper head Stop and Clear positions and yellow lenses everywhere else. In the 1980's Amtrak modified post of its former-PRR position lights to use the equivalent color light colors in all of the positions of both heads. Internally referred to as Position Color Lights these should not be confused with Color Position Lights described below.
New PRR type position lights continued to be installed up until the 1980's on former Conrail systems. Today most of the old PRR PL's are slowly being replaced by regular modular color lights, but Amtrak and the LIRR continue to install new position lights, Amtrak's being of the colorized variety. US&S no longer manufactures position light equipment, but updated models from Safetran Systems continue to be available.
Color position light
The Color Position Light (CPL) signal was invented by the Baltimore and Ohio railroad in the 1920's and a proprietary all electric signal aspect system to replace electro-mechanical semaphores. The CPL system was unique in the fact that it was designed from scratch instead of being based as an update to the existing semaphore based aspects. The B&O CPL system incorporates several design principles that are otherwise unique to North American signaling. These include:
- Fully failsafe design, any bulb failure will not result in a less restrictive aspect being displayed.
- Common signal aspects for dwarf and high signals.
- Use of the color red ONLY in the case of an absolute stop or restricted speed situation.
The CPL consists of a central position target with up to 4 pairs of main color lamps spaced around the edge of the target at 45o intervals using the positions: green |, yellow /, red -- and a lunar white \ also being present sometimes. The main head was surrounded by up to 6 so-called "orbitals" at the 12, 2, 4, 6, 8 and 10 o'clock positions. The function of the main head was block occupancy information with green representing 2 or more clear blocks, yellow 1 clear block and red/lunar white representing no clear blocks. The orbitals would then serve to provide speed information, 12 o'clock being Normal speed, 6 being Medium speed (Limited speed if flashing), 10 being Full to Medium (Limited if flashing), 2 being Full to Slow, 8 being Medium to Medium, 4 being Medium to Slow and no lit orbitals being Slow to Slow.
This CPL was first deployed on the Staten Island Railroad (a B&O subsidiary) the 1920's and then deployed system wide shortly thereafter. Later parts of the Chicago and Alton Railroad received CPLs when the B&O gained control of that line as well. In the 1980's both Amtrak's Chicago Union Station and Metra's Chicago Northwestern Station installed dwarf CPL's to replace earlier signals in those terminals.
As of 2008, CSX is slowly replacing all of the remaining CPLs on its system with modular "Darth Vader" style color light signals. The signals on the old Alton have also been almost entirely replaced as have many of the CPL dwarfs at the two Chicago terminals. The sole exception is the Staten Island Railroad, which recently upgraded its signaling system with new CPL's using modern Safetran PL equipment.
Semaphore
Semaphore signals have almost been completely replaced by all electric signals in North America, but they contain several important design elements. The overwhelming majority of semaphore type signals used in North America, and the only type surviving in service as of 2008 are of the three position, upper quadrant variety. Those of the lower quadrant variety would typically have two positions, but three lenses, two being of the more restrictive type. This was to reduce the chance of a malfunction or snowfall causing the signal to drop to its less restrictive position.
North American semaphores have been worked by electric motor since the advent of the track circuit block system make some form of automation necessary. Some dwarf signals were worked mechanically to give Restricting type signals which did not rely on track circuits, but motorized dwarfs were more common. As early as 1915, the cost associated with semaphore maintenance as well as visibility issues have spurred railroads to replace then with all electric systems, such as the searchlight. Like the searchlight, the semaphore operation with a low power light source and infrequent moving of the blade worked well with a battery powered signaling system far from any regular power source.
As of 2008 active semaphores exist on a few segments of main line railroad in the west and on a former Monon Railroad branch line in Indiana.
Common Signal Rule Classes
Most North American railroads have between 10 to 20 separate signal rules, each which are often represented by multiple aspects. However, all of these complicated rules revolve around the simple premise of informing the locomotive engineers how they need to be handling their train at the present point and what they can expect at the next signal.5 From here the large set of rules and aspects can be broken down into a small number of classes which are common to all North American signaling systems.
- Automatic Block - Block aspects convey basic track occupancy information and are the most basic signal rules common to all railroads. These include Clear, Advance Approach and Approach which report to the engineer "expect no stop", "expect stop at second signal" and "except stop at next signal" respectively. Advance approach is only used in situation with short signal blocks to ensure trains have enough stopping distance. These are the most common signal aspects in North America and are the only aspects most automatic block signals need to display.
- Approach at Speed - When a train needs to be told to slow down due to dynamic conditions an "Approach Speed" aspect is used. These inform the engineer to slow to a prescribed speed by the next signal. The most common reason for this is that the train is to take a diverging, or non-Normal speed route at the next interlocking. Signals of this type include Approach Medium, Approach Limited, Approach Slow and Approach Diverging. These signals are typically displayed on the distant signal to an interlocking, but can sometimes be used with short signal blocks in place of Advance Approach.
- Diverge to Clear - This class appears only on absolute signals and informs the engineer that the train will be taking a diverging route and the train will not expect a stop at the next signal. In speed signaling the engineer is informed of the speed the train needs to take the route at, in weak route signaling the engineer is just informed of a diverging route. Signals in this class include Medium Clear, Slow Clear, Limited Clear and Diverging Clear.
- Diverge to Stop - Same as above only the train can except to stop at the signal after the interlocking. These signals include Medium Approach, Slow Approach and Diverging Approach.
- Combination Signals - These combine functions of a "Diverge to" signal with an "Approach Speed" signal and occur in areas of complex trackwork where there are no intermediate signals between one interlocking and the next. In the United States only a few combination signals like Medium Approach Medium, Medium Approach Slow and Diverging Approach Medium/Slow are ever found in rulebooks and not frequently used in practice. The Canadian standard rulebook contains signal rules and aspects for every possible combination.6
- Restricted Speed Signal - This class of signals are displayed for trains moving into a block where a track circuit has been de-energized or does not exist. A "shunted" track circuit indicates a either the block is occupied by another train or railcar, or there is a problem such as a broken rail or flooded track. Where a track is not protected by track circuits that track must be presumed to be occupied. As the name implies this signal requires trains to move at Restricted speed, specifically with the ability to stop short of an obstruction. Restricted speed signals take many forms including Restricting and Restricted Proceed where trains must simply pass the signal at restricted speed and also Stop and Proceed, where a train must come to a complete stop before proceeding at restricted speed. Stop and Proceed has fallen out of favor with most freight railroads due to the fuel and time savings of allowing the trains to not come to a complete stop. This aspect class can be displayed on almost all in North America.
- Stop Signal - Stop signals are displayed on Absolute signals, in fact the ability to display an absolute Stop is part of that signal type's definition. Stop is the most important signal as passing a signal at Stop presents a serious risk of accident. Engineers committing a Stop signal violation automatically have their Federal certification suspended and are frequently fired. Stop signals can only be passed upon special permission from a control authority.
- Cab Signaling Signals - Where cab signaling is employed without fixed trackside automatic signals, special signal aspects are required at absolute signals. These include some sort of absolute block "Super Clear" signal that allows passage to the next interlocking with a fixed signal and also the "Cab Speed" signal that informs the engineer to proceed under direction of cab signals.
Distant (approach) signals
A distant signal can either be an automatic signal before an interlocking, or the interlocking signal itself when interlockings are back to back. Distant signals typically display more aspects than a typical block or interlocking signal to warn trains of diverging movements at the next interlocking however this is not always the case if there are no diverging paths available.
Distant signals are often referred to as Approach Signals as the signal block before the interlocking is known as the approach block. When a train enters the approach block any route lined up at the interlocking will become locked in place until a timer is run to prevent routeing a conflicting movement without giving the approaching train adequate time to come to a stop.
In the aftermath of the 1996 Silver Spring Collision the Federal Railroad Administration amended its regulations for push-pull train operation to prevent locomotive engineers from forgetting that they were approaching a stop signal after making a station stop. The resulting Delay in Block Rule required that all distant signals in territory where push-pull trains operated in the absence of cab signals were to be marked with a 'D' placard to remind engineers that they were bound by a 40 mph speed restriction between any station stop and the point where the home signal became visible.
Example Signals and aspects
CSX/Chessie System Signal Rules
These signals are seen on CSX's former Chessie System (C&O and B&O) territory.
Note: Images are placed side by side for a clearer perspective on the possible light configurations. Under normal conditions there may only be one or two light trees. There are also two different types of signals shown here. The stick lights, and the large round lights are two different designs that would not normally be seen together.
| Rule number | Rule | Rule description and procedure | Signal aspect |
|---|---|---|---|
| 281 | Clear | Clear to proceed at normal track speed. |     |
| 281(b) | Approach Limited |
Proceed to next signal at limited speed. |    |
| 281(c) | Limited Clear |
Limited Speed through turnouts, crossovers, sidings, and over power-operated switches; then proceed. |
    |
| 281(d) | Limited Aproach |
Limited Speed through turnouts, crossovers, sidings, and over power-operated switches; then proceed, prepared to stop at next signal. |
  |
| 282 | Approach Medium |
Proceed, approaching next signal not exceeding Medium Speed. |    |
| 283 | Medium Clear |
Medium Speed through turnouts, crossovers, sidings, and over power-operated switches; then proceed. |
   |
| 283(a) | Medium Approach Medium |
Medium Speed through turnouts, crossovers, sidings, and over power-operated switches; then proceed approaching next signal not exceeding Medium Speed. |
  |
| 283(b) | Medium Approach Slow |
Medium Speed through turnouts, crossovers, sidings, and over power-operated switches; then proceed approaching next signal not exceeding Slow Speed. |
  |
| 284 | Approach Slow |
Proceed, approaching next signal not exceeding Slow Speed. |    |
| 285 | Approach | Proceed prepared to stop at the next signal. Trains exceeding medium speed must immediately begin reduction to medium speed as soon as the engine passes the Approach Signal. |
   |
| 285(a) | Distant Signal |
Approach next signal prepared to stop. NOTE: This signal provides information only about the next signal, not conditions of the track ahead. | (semaphore) |
| 286 | Medium Approach |
Medium Speed through turnouts, crossovers, sidings, and over power-operated switches; then proceed prepared to stop at next signal. |
  |
| 287 | Slow Clear |
Slow Speed through turnouts, crossovers, sidings, and over power-operated switches; then proceed. |
  |
| 287(a) | Slow Approach Slow |
Slow Speed through turnouts, crossovers, sidings, and over power-operated switches; then proceed approaching next signal not exceeding Slow Speed. |  |
| 288 | Slow Approach |
Slow Speed through turnouts, crossovers, sidings, and over power-operated switches; then proceed prepared to stop at next signal. |   |
| 290 | Restricting | Proceed at Restricted Speed. |    |
| 291 | Stop | STOP, then proceed at Restricted Speed. |    |
| 292 | Stop | STOP. |     |
| 295 | Approach | Proceed, approaching next signal as authorized by the aspect displayed. If signal is dark, proceed prepared to stop at next signal until it can be plainly seen that indication of next signal allows train to proceed. | Signal, black, APP on round white marker below |
| 296 | Doll Arm |
A track intervenes between the signal and the track governed by the signal. | |
| 297 | Adjacent or Bracketed Signals |
Proceed, approaching next signal as authorized by the aspect displayed. If signal is dark, proceed prepared to stop at next signal until it can be plainly seen that indication of next signal allows train to proceed. | |
| 298 | Grade | Proceed at Restricted Speed. |  |
Definitions
Absolute Block - a block that may be occupied by only one train at a time.
Absolute Signal - a color light, color position light, or semaphore signal without a number plate, "P" marker, APP" marker, "C" marker, or "G" marker, that conveys Stop as its most restrictive aspect. Automatic Block Signal System (ABS)- a series of consecutive blocks whose use is governed by train[-]actuated block signals or by certain conditions affecting the use of a block. Unless so specified, such signals do not authorize the movement of trains.
Block - a track section of defined limits. In signaled territory, a block is the track section between two consecutive block signals governing movements in the same direction. It is also the track section from a block signal to the end of signaled territory.
Block Signal - an absolute or intermediate signal at the entrance to a block that governs the movement of trains using that block.
Color Light Signal - a fixed signal that displays aspects by the color of a light. It may also display aspects by a combination of colored lights.
Color Position Light Signal (CPL) - a fixed signal that displays aspects by the color or position of two or more lights.
Current of Traffic - the movement of trains on a main track, in one direction, as specified by the rules or special instructions.
Direct Traffic Control Block - a block whose use is governed by verbal authority of the train dispatcher.
Fixed Signal - a permanent signal or sign indicating a condition affecting train movement.
Interlocking - an arrangement of interconnected signals and signal appliances for which interlocking rules are in effect. Signals and movement of signal appliances must succeed each other in proper sequence.
Interlocking Signals - fixed signals of an interlocking.
Intermediate Signal - a block signal equipped with either a number plate, a "G" marker, or "P" marker. It conveys Stop and Proceed at Restricted Speed as its most restrictive indication.
Main Track - a track extending through yards and between stations. It is other than an auxiliary track.
Siding - an auxiliary track for meeting or passing trains. It is designated in special instructions.
Traffic Control Signal System (TCS) - a signal system under which opposing and following train movements are authorized and governed by block signals.
Train - an engine, with or without cars, displaying a marker.
Sign post signals
Speeds
| Rule number | Rule | Rule description and procedure | Signal aspect |
|---|---|---|---|
| 297 | Controlled Speed | a speed that will permit stopping within one-half the range of vision. It will also permit stopping short of a train, a car, an obstruction, on-track equipment or a stop signal. | |
| 298 | Limited Speed | a speed not exceeding 45 miles per hour. Shown here are: (A) advanced warning (B) limited speed zone indicator. | (A)  (B)  |
| 298 | Medium Speed | a speed not exceeding 30 miles per hour. | |
| 298 | Restricted Speed | a speed that will permit stopping within one-half the range of vision. It will also permit stopping short of a train, a car, an obstruction, on-track equipment or a stop signal, a derail, or an improperly lined switch. It must permit looking out for broken rail. It will not exceed 15 MPH. The limit signs are marked with S and the resume speed signs are marked with the letter R. (A) Advance warning of restricted speed. (B) Restricted speed. (C) Temporary restricted speed. (D) Resume speed. (E) Resume speed from temporary restriction. | (A) (B)  (C) (D) (E) |
| 298 | Slow Speed | a speed not exceeding 15 miles per hour. |
Other forms of signals
- Whistle posts are marked with a "W" signaling the engineer to begin, or prepare to sound the horn.
| Rule number | Rule | Rule description and procedure | Signal aspect |
|---|---|---|---|
| 14(l) | Whistle post | a warning signal for the engineer of a train that he/she is approaching a road crossing, or "Grade crossing" as they are often called. |
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References
- ^ http://broadway.pennsyrr.com/Rail/Signal/significance.html
- ^ http://broadway.pennsyrr.com/Rail/Signal/learning_the_aspects.html
- ^ http://www.prrths.com/PRR_Signals.html
- ^ http://broadway.pennsyrr.com/rail/Prr/Maps/Itlk/overbrook.gif
- ^ http://broadway.pennsyrr.com/Rail/Signal/aspect_speeds.html
- ^ http://www.trainweb.org/railwayop/Signals2/signal2a.html
- John Armstrong, "All About Signals" (Two-article series). Trains Magazine, June and July 1957.
- The Pennsylvania Railroad rules for conducting transportation, October 28, 1956
- The Pennsylvania Railroad rules for conducting transportation, April 28, 1968
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