A highway-rail grade crossing can be viewed as simply a special type of highway intersection, in that the three basic elements of any intersection are present: the driver, the vehicles, and the physical intersection. As with a highway intersection, drivers must appropriately yield the ROW to opposing traffic; unlike a highway-highway intersection, the opposing traffic–the train– is not required to yield the ROW to the highway vehicle. Drivers of motor vehicles have the flexibility of altering their path of travel and can alter their speed within a short distance. Train operators, on the other hand, are restricted to moving their trains down a fixed path, and changes in speed can be accomplished much more slowly. Because of this, motorists bear most of the responsibility for avoiding collisions with trains.

The railroad Crossbuck sign is defined in the MUTCD as a regulatory sign. In effect, it is a YIELD sign, and motorists have the obligation to so interpret it. Traffic and highway engineers can assist motorists with the driving task by providing them with proper highway design, adequate sight distances, and proper traffic control devices.

The components of a highway-rail grade crossing are divided into two categories: the highway and the railroad. The highway component can be further classified into several elements including the roadway, drivers, pedestrians and bicyclists, and vehicles. The railroad component is classified into train and track elements. The location where these two components meet should be designed to incorporate the basic needs of both highway vehicles and trains.

Traffic control devices are utilized to provide road users with information concerning the crossing. Typically, an advance warning sign and pavement markings inform the motorist that a crossing lies ahead in the travel path. The crossing itself is identified and located using the Crossbuck. These traffic control devices–the advance sign, pavement markings, and Crossbuck–are termed "passive" because their message remains constant with time.

"Active" traffic control devices tell the motorist if a train is approaching or occupying a crossing and, thus, give a variable message. Typical active traffic control devices are flashers or flashers and automatic gates. A highway traffic signal may also be interconnected to the crossing signals and would form part of the traffic control system at the crossing.

The USDOT National Highway-Rail Crossing Inventory provides information on the number of crossings having each type of traffic control device, as shown in Table B-1.

HIGHWAY COMPONENTS

Driver

The driver is responsible for obeying traffic control devices, traffic laws, and the rules of the road. Highway and railroad engineers who plan and design initial installations or later improvements to traffic control systems at railroad grade crossings should be aware of the several capabilities, requirements, needs, and obligations of the driver. This information will help them, through the proper engineering design of improvements, assisting drivers in meeting their responsibilities.

Table B-1. Public Crossings by Warning Device, 2017

Warning device	Number	Percent
Active devices
Gates	50,018	39.16
Flashing lights	17,613	13.79
Highway signals, wigwags, or bells	1,326	1.04
Speciala	908	0.71
Total active	69,865	54.69
Passive devices
Crossbucks	43,289	33.89
STOP signs	11,877	9.30
Other signs	265	0.21
Total passive	55,431	43.39
No signs or signals	2,442	1.91
Total	127,738	100.00

^aNote: "Special" are traffic control systems that are not train activated, such as a crossing being flagged by a member of the train crew.

Source: Federal Railroad Administration.¹

This section deals with the duties of the motor vehicle driver.

As of 2000, the Uniform Vehicle Code (UVC) is a specimen set of motor vehicle laws designed or advanced as a comprehensive guide or standard for State motor vehicle and traffic laws.⁽⁸⁶⁾ It describes the actions a driver is required to take at highway-rail grade crossings. The UVC defines the "appropriate actions" vehicle operators are required to take for three situations: vehicle speed approaching the crossing; vehicle speed traversing the crossing; and stopping requirements at the crossing. The provisions in UVC for these actions are set out below:

• Approach Speed (Sec. 11-801).
  • No person shall drive a vehicle at a speed greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing. Consistent with the foregoing, every person shall drive at a safe and appropriate speed when approaching and crossing an intersection and railroad grade crossing....
• Passing (Sec. 11-306).
  1. No vehicle shall be driven on the left side of the roadway under the following conditions...
     ...2. When approaching within 100 feet of or traversing any intersection or railroad grade crossings unless otherwise indicated by official traffic control devices...
• Vehicles Approaching a Highway-Rail Grade Crossing (Sec. 11-701)
  1. Whenever any person driving a vehicle approaches a railroad grade crossing under any of the circumstances stated in this section, the driver of such vehicle shall stop within 50 feet but not less than 15 feet from the nearest rail of such railroad, and shall not proceed until it is safe to do so. The foregoing requirements shall apply when:
     1. A clearly visible electric or mechanical signal device gives warning of the immediate approach of a railroad train;
     2. A crossing gate is lowered or when a human flagger gives or continues to give a signal of the approach or passage of a railroad train;
     3. A railroad train approaching within approximately 1,500feet of the highway crossing emits a signal audible from such distance, or such railroad train by reason of its speed or nearness to such crossing is an immediate hazard;
     4. An approaching railroad train is plainly visible and is in hazardous proximity to such crossing.
  2. No person shall drive any vehicle through, around or under any crossing gate or barrier at a railroad crossing while such gate or barrier is closed or is being opened or closed.
• Designated Vehicles Must Stop at Highway-Rail Grade Crossings (11-702)
  1. Except as provided in subsection (b), the driver of any vehicle described in regulations issued pursuant to subsection (c), before crossing at grade any track or tracks of a railroad, shall stop such vehicle before the stop line (if present) and not less than 15 feet from the nearest rail of such track, and while so stopped shall listen and look in both directions along such track for any approaching train and for signals indicating the approach of a train and shall not proceed until it is safe to do so. After stopping as required, upon proceeding when it is safe to do so, the driver shall cross only in a gear of the vehicle that will not require manually changing gears while traversing such crossing and the driver shall not manually shift gears while crossing the track or tracks.
  2. This section shall not apply at:
     1. Any railroad grade crossing at which traffic is controlled by a police officer or flagger;
     2. Any railroad grade crossing at which traffic is regulated by a traffic-control signal;
     3. Any railroad grade crossing protected by crossing gates or an alternately flashing light signal intended to give warning of the approach of a railroad train;
     4. Any railroad grade crossing at which an official traffic control device gives notice that the stopping requirement imposed by this section does not apply.
  3. The (commissioner or other appropriate State official or agency) shall adopt regulations, as may be necessary, describing the vehicles that must comply with the stopping requirements of this section. In formulating those regulations, the (commissioner or other appropriate State official or agency) shall give consideration to the number of passengers carried by the vehicle and the hazardous nature of any substance carried by the vehicle in determining whether such vehicle shall be required to stop. Such regulations shall correlate with, and so far as possible, conform to the most recent regulation of the United States Department of Transportation.

Each State has its own traffic laws, which may vary from those above. The pertinent sections of the State code and the State driver licensing handbook should be consulted for more information.

Vehicle

The design and operation of a railroad grade crossing should reflect the number and types of vehicles that can be expected to use it. In this regard, crossings are exposed to the full array of vehicle types found on highways, from motorcycles to truck tractor/triple-trailer combinations, although the use of crossings by the largest vehicle types is rare. Typically, the largest vehicles that will use an at-grade crossing are full-size passenger buses or design trucks such as WB-50. The vehicles utilizing highway-rail grade crossings have widely different characteristics that will directly influence the design elements of the crossing. Equally important is the cargo these vehicles carry, especially children in school buses and hazardous materials in trucks.

Table B-2 summarizes collisions at crossings by vehicle type. Rates are defined as collisions per billion miles of travel. The data provides some indication of the relative hazards for each of the vehicles. Trucks have the highest collision rates of all vehicle types. Motorcycles have a higher fatality rate, probably because of the lack of operator protection provided by the vehicle.

Several physical and performance characteristics influence the safety of vehicles at crossings. These include vehicle dimensions, braking performance, and acceleration performance.

Vehicle Dimensions

The length of a vehicle has a direct bearing on the inherent safety of the vehicle at a grade crossing and, consequently, is an explicit factor considered in the provision of sight distances. Long vehicles and vehicles carrying heavy loads have longer braking distances and slower acceleration capabilities; hence, long vehicles may be exposed to a crossing for an even greater length of time than would be expected in proportion to their length.

Vehicle length is explicitly considered in determining the effect of sight distance, and the corner sight triangle on the safe vehicle approach speed toward the crossing and in determining the sight distance along the track for vehicles stopped at the crossing. The design lengths of various vehicles are specified by the AASHTO and shown in Table B-3.

Table B-2. Motor Vehicle Collisions and Casualties at Public Crossings by Vehicle Type, 2017

–	Automobilesa	Buses	Trucksb	Motorcycles	Total
Total collisions
Number	1,828	7	587	9	2,431
Ratec	0.67	1.05	2.59	0.90	0.84
Percent	75.19	0.29	24.15	0.37	100.00

–	Automobilesa	Buses	Trucksb	Motorcycles	Total
Total fatalities
Number	204	0	35	2	241
Ratec	0.08	0.00	0.15	0.20	0.08
Percent	84.65	0.00	14.52	0.83	100.00

–	Automobilesa	Buses	Trucksb	Motorcycles	Total
Total injuries
Number	648	7	225	5	885
Ratec	0.24	1.05	0.99	0.50	0.31
Percent	73.22	0.79	25.42	0.57	100.00

–	Automobilesa	Buses	Trucksb	Motorcycles	Total
Vehicle miles of travel (billions)	2,719.32	6.64	226.51	10.05	2,890.89
Registered vehicles	228,276,000	795,000	8,171,000	5,781,000	236,761,000
Collisions per million vehicles	8.01	8.81	71.84	1.56	10.27

^a "Automobiles" includes passenger cars, pick-up trucks, vans, and sport utility vehicles.

^b "Trucks" includes both single-unit trucks and combination trucks.

^c "Rate" is the number of collisions, fatalities, or injuries divided by billions of vehicle miles traveled. Source: FRA and FHWA.

Table B-3. U.S. Customary Lengths for Design Vehicles

Design vehicle type	Designation	Length (feet)
Passenger car	P	19
Single-unit truck	SU	30
Buses
Intercity bus (motor coaches)	BUS-40	40
	BUS-45	45
City transit bus	CITY-BUS	40
Conventional school bus (65 passengers)	S-BUS 36	35.8
Large school bus (84 passengers)	S-BUS 40	40
Articulated bus	A-BUS	60
Trucks
Intermediate semitrailer	WB-40	45.5
Intermediate semitrailer	WB-50	55
Interstate semitrailer	WB-62*	68.5
Interstate semitrailer	WB-65** or WB-67	73.5
"Double-bottom" semitrailer/trailer	WB-67D	73.3
Triple-semitrailer/trailers	WB-100T	104.8
Turnpike double-semitrailer/trailer	WB-109D*	114
Recreational Vehicles
Motor home	MH	30
Car and camper trailer	P/T	48.7
Car and boat trailer	P/B	42
Motor home and boat trailer	MH/B	53

*Design vehicle with 48-foot trailer as adopted in the 1982 Surface Transportation Assistance Act.

**Design vehicle with 53-foot trailer as adopted grandfathered in with the 1982 Surface Transportation Assistance Act.

Source: From A Policy on Geometric Design of Highway and Streets, 2011, by the American Association of State Highway and Transportation Officials, Washington, DC. Used by permission.

The AASHTO recognizes 20 design vehicle classes. This reflects the increase in the size of tractor-semitrailers, which began with the passage of the Surface Transportation Assistance Act of 1982, as well as the increasing presence of articulated buses in the U.S. transit fleet and the increasing popularity of recreational vehicles and motor homes.⁽⁸⁷⁾

Unless trucks are prohibited at the crossing, it is desirable that the design vehicle be at least a tractor-semitrailer truck (WB-15 SI Metric, or WB-50). Typically, the design vehicle should be a "double-bottom" vehicle (WB-18 SI Metric, or WB-60) for those crossings on routes designated for longer trucks, although consideration should be given especially to long vehicles where applicable. On major arterials with significant truck traffic, the design vehicle should be an "interstate" semitrailer truck (WB-62 or WB-65).

The width of the vehicle may be an issue when selecting the crossing surface. Since the passage of the 1982 STAA, trucks and intercity buses are permitted to have widths of 102 inches, as indicated in Table 2-1b of the AASHTO: A Policy on Geometric Design of Highways andStreets/*⁷

Braking Performance

One component of stopping sight distance is a function of a vehicle's braking performance. If a crossing experiences a significant percentage of heavy trucks, any given sight distance will dictate a slower speed of operation to allow for the braking performance of these vehicles.

Acceleration Performance

Acceleration of vehicles is important to enable a stopped vehicle to accelerate and clear the crossing before a train that was just out of sight or just beyond the train detection circuitry reaches the crossing. Large trucks that have poor acceleration capabilities coupled with long lengths are particularly critical in this type of situation.

There are three phases of operation for a truck that has stopped at a crossing: start-up when the clutch is being engaged; acceleration from the point of full clutch engagement; and continued travel until the crossing is cleared.

Another aspect of the acceleration performance of vehicles at crossings is the design of the crossing approaches coupled with the condition of the crossing surface. Crossings and approaches on a steep grade are difficult and time-consuming to cross. Also, vehicles will move more slowly over crossings that have rough surfaces.

Special Vehicles

The following three vehicle types are of particular concern for crossing safety: trucks carrying hazardous materials; any commercial motor vehicle transporting passengers; and school buses. Collisions involving these vehicles can result in numerous injuries and/or fatalities, perhaps in catastrophic proportions if certain hazardous cargoes are involved.

In a special study conducted by the NTSB, it was determined that an average of 62 collisions involving a train and a truck transporting hazardous materials occur annually. NTSB's examination of the collision data revealed that these collisions tend to occur near truck terminals.⁽⁸⁸⁾

Requirements for commercial vehicles to stop or slow at highway-rail grade crossings are contained in 49 CFR 392.10, which requires that the driver of a specified commercial motor vehicle:

Except as provided in paragraph (b) of this section, the driver of a commercial vehicle specified in paragraphs (a) (1) through (6) of this section shall not cross a railroad track or tracks at grade unless he/she first: Stops the commercial motor vehicle within 50 feet of, and not closer than 15 feet to, the tracks; thereafter listens and looks in each direction along the tracks for an approaching train; and ascertains that no train is approaching. When it is safe to do so, the driver may drive the commercial motor vehicle across the tracks in a gear that permits the commercial motor vehicle to complete the crossing without a change of gears. The driver must not shift gears while crossing the tracks.

Vehicles to which this rule pertains include but are not limited to the following:

• Every bus transporting passengers and vehicles transporting migrant workers. ("Bus" is defined at 49 CFR 390.5 as "as any motor vehicle designed, constructed, and or used for the transportation of passengers, including taxicabs.")
• Every commercial motor vehicle which, in accordance with the regulations of USDOT, is required to be marked or placarded with hazardous materials including the following:
  • Poison Gas
  • Flammables
  • Chlorine
  • Poison
  • Oxygen
  • Combustible liquids

As required by 49 CFR 398.4, all such motor vehicles shall display a sign on the rear reading, "This Vehicle Stops at Railroad Crossings."

Finally, 49 CFR 392.11 provides that:

Every commercial motor vehicle other than those listed in §392.10 shall, upon approaching a railroad grade crossing, be driven at a rate of speed which will permit said commercial motor vehicle to be stopped before reaching the nearest rail of such crossing and shall not be driven upon or over such crossing until due caution has been taken to ascertain that the course is clear

Provisions to enhance safety for these special vehicles are further discussed in Chapter 6, Special Topics.

Pedestrians

In 2017, collisions involving pedestrians at crossings accounted for 8.1 percent, or 172, of all crossing collisions. As might be expected, these collisions almost always result in an injury or fatality. In 2017, there were 86 pedestrian fatalities, comprising 31.7 percent of all crossing fatalities. These statistics do not include pedestrian collisions occurring elsewhere along railroad tracks. Excluding collisions and incidents at crossings, 535 trespasser fatalities occurred on railroad property during 2017. This represents 63 percent of all railroad-related fatalities.

Table B-4 shows the number of highway-rail grade crossing collision fatalities and trespasser fatalities from 2008 to 2017. During this 10-year period, crossing collision fatalities and trespasser fatalities fluctuated. Each year since 2008, the number of trespasser fatalities has been greater than the number of highway-rail grade crossing collision fatalities.

Table B-4. Highway-Rail Grade Crossing Collision Fatalities versus Trespasser Fatalities, 2008-2017

Year	Highway-Rail Grade Crossing Collision Fatalities	Trespasser Fatalities
2008	290	457
2009	248	416
2010	261	441
2011	246	399
2012	231	405
2013	232	427
2014	262	470
2015	236	449
2016	253	465
2017	271	535

Source: Federal Railroad Administration Safety Data website (safetydata.fra.dot.gov/officeofsafety).²

² Updated data can be found on the FRA's Office of Safety Analysis website (also known as Safetydata) at https://safetydata.fra.dot.gov.

Roadway

A major component of the crossing is the physical configuration of the highway on the approach and at the crossing itself. The following roadway characteristics are relevant to the design and control of highway-rail grade crossings:

• Location–urban or rural
• Type of road–arterial, collector, or local
• Traffic volumes
• Geometric features–number of lanes, horizontal and vertical alignment, sight distance, crossing angle, etc.
• Crossing surface and elevation
• Nearby intersecting highways
• Illumination

Urban crossings often carry more vehicular traffic than rural crossings and have sight restrictions due to developed areas. Urban crossings also involve obstructions to continuous traffic flow, such as controlled intersections, driveways, business establishments and distracting signs, significant lane interaction, and on-street parking.

All other factors being the same, for a given train volume, collision frequency increases with increasing traffic volume. However, traffic volume alone is not a sufficient forecaster of collisions at crossings.

The geometric features that can affect traffic operations at highway-rail grade crossings include the following:

• Number of lanes and pavement width
• Horizontal and vertical alignment
• Crossing angle
• Crossing elevation

These features, in turn, affect sight distances to and at crossings. Number of Lanes

Less than 10 percent of all public crossings are on highways with more than two lanes.⁽⁷⁵⁾ It is not known how many crossings with two lanes have an approach width greater than two lanes. The reduction of lanes at a crossing can cause vehicle-vehicle collisions as well as collisions with trains.

At two-lane crossings, a pullout lane may be provided for trucks or buses that may be required to stop for the crossing. By providing a pullout lane, the likelihood of rear-end collisions may be reduced.

Crossings with more than two lanes are usually candidates for cantilevered flashing light signals to improve the visibility of the signals for drivers.

Horizontal Alignment

Sight distance to the crossing is affected by the vertical and horizontal alignment of the crossing and by the crossing angle. Crossings located around a curve or over the crest of a hill may require special attention from the motorist and may need additional signing or active advance warning devices. For new crossings, or major reconstruction, it is desirable to have the crossing angle as close to 90 degrees as possible.

Crossing and Approach Surfaces

The roughness of a crossing surface and the profile of the surface and its approaches may be major areas of concern for road users. A rough surface may contribute to a collision by diverting the road user's attention from the prime tasks of observing the crossing signals and looking for a train.

Crossing Elevation or Profile

Another aspect of the crossing is its elevation. Vehicles that cross the tracks from a stopped position cannot accelerate quickly on steep grades. In addition, trucks with low ground clearances may become trapped on high-profile or "hump-backed" crossings, delaying highway and rail traffic and, possibly, being struck by a train.

Intersecting Highways

Frequently, roads parallel the railroad, and intersecting roads intersect the railroad, resulting in a crossing near the highway intersection. The higher occurrence of collisions at these intersections is due in part to a short storage area for vehicles waiting to move through the crossing and the intersection. If the intersection is signalized or if the approach from the crossing is controlled by a STOP sign, queues may develop across the crossing, leading to the possibility of a vehicle becoming "trapped" on the crossing. Also, there are more distractions to the motorist, leading to the possibility of vehicle-vehicle conflicts.

Crossings within a close distance to a signalized or STOP-controlled intersection should be carefully evaluated for proper controls. STOP controls should be evaluated where either the crossing or the intersection, or both, is not signalized. Traffic signal timing should be carefully evaluated, and an interconnection circuit installed if needed. Joint inspections of interconnected or preempted signals by the railroad and the highway agency should be made on a regular basis to assure that the crossing signals and the highway traffic signal are functioning properly and that the phasing and timing plans are still appropriate.

The critical distance between a highway-rail crossing and a highway-highway intersection is a function of the number of vehicles expected to be queued up by the intersection traffic control.

For additional information, refer to MUTCD Section 4D.27 Preemption and Priority Control of Traffic Control Signals.

Illumination

Illumination of the crossing can definitely aid the motorist. Illumination may be effective in reducing collisions at night; as it will assist road users, including bicyclists and pedestrians, in traversing the crossing at night. USDOT Inventory reports that commercial power is available at more than 90 percent of public crossings. Therefore, lighting is feasible at most crossings; depending, of course, on the reliability of the power source.

Traffic Control Devices

The responsibility for the design, placement, operation, and maintenance of traffic control devices normally rests with the governmental body having jurisdiction over the road or street. For the purpose of installation, operations and maintenance of devices constituting traffic control devices at highway-rail grade crossings, it is recognized that any crossing of a public road with a railroad is situated on a right of way that is available for the use of both highway traffic and railroad traffic on their respective roadway and tracks. This requires joint responsibility in the traffic control function between the public agency and the railroad.

The determination of need and the selection of devices at a grade crossing are normally made by the public agency having jurisdiction. Subject to such determination, the design, installation, and operation of such devices shall be in accordance with the principles and requirements set forth in MUTCD.

Due to the character of operations and the potentially severe consequences of collisions, traffic control devices at highway-rail grade crossings and on the approaches thereto need to be viewed as a system. The combination of approach signs and pavement markings on the roadway approach and the Crossbucks or signals at the crossing provides the road user with multiple notices of the presence of the crossing and the likelihood of encountering a train.

For those sections where rail tracks run within a roadway, which is a common practice for light rail and streetcar operations, traffic control may be provided by a combination of signs, pavement markings, and typical "highway" type control devices such as STOP signs and traffic signals. However, for the broader case, where rail tracks are in a separate ROW with designated crossings of highways and pedestrian pathways, traffic is typically controlled with one of three types of devices, each requiring a distinct compliance response per the UVC, various Model Traffic Ordinances and State regulations:

• A Crossbuck is a type of YIELD sign–The driver should be prepared to stop at least 15 feet before the near rail unless, and until, the driver can make a reasonable decision that there are no trains in hazardous proximity to the crossing and it is safe to cross.
• Operating flashing lights have the same function as a STOP sign–A vehicle is required to stop completely at least 15 feet short of the near rail. Then, even though the flashing lights may still be operating, the driver can proceed after stopping (subject to State or local laws), when safe to do so.
• Flashing lights with lowered gates are equivalent to a red vehicular traffic signal indication– A vehicle is required to stop short of the gate and remain stopped until the gates go up.

Motorist comprehension and compliance with each of these devices is mainly a function of education and enforcement. The traffic engineer should make full use of the various traffic control devices as prescribed in MUTCD to convey a clear, concise, and easily understood message to the driver.

RAILROAD COMPONENTS

Train

Headlights

FRA regulations require that, for locomotives operated through one or more public highway-rail grade crossings at speeds greater than 20 miles per hour, auxiliary lights are to be placed at the front of the locomotive to form a triangle with the headlight.⁽⁸⁹⁾ The inclusion of auxiliary lights helps crossing users determine the distance and approximate speed of an approaching train.⁽⁹⁰⁾

Train Horns

Locomotives are equipped with air-powered horns to sound a warning of a train's approach to a crossing and for various other signals in railroad operations. FRA requires the horn to produce a minimum sound level of 96db(A) and a maximum of 110 db(A) at 100 feet forward of the locomotive. The locomotive engineer sounds the horn in advance of a crossing in a sequence of two long blasts, followed by a short blast, then followed by one long blast. Additional information can be found under Title 49 CFR 222.21 and Title 49 CFR 229.129.^(89, 91)

Reflectorization

FRA regulations governing the reflectorization of rail freight rolling stock (49 CFR Part 224) apply to "railroad freight cars and locomotives that operate over a public or private highway-rail grade crossing and are used for revenue or work train service."⁽⁹²⁾

These reflectorization regulations require railroads to install yellow or white reflective materials on freight cars and locomotives before placing them in service. Figure B-1 illustrates the application on a typical freight car.

Figure B-1. Reflectorization Example–Standards Applicable to Boxcars

Source: Reflectorization of Rail Freight Rolling Stock final rule, 70 FR 62166 (October 28, 2005).

Braking

Primarily because of their enormous weight, railroad trains are slow to accelerate and decelerate. Numerous factors affect a train's acceleration capability, such as the number of locomotive units, the horsepower rating of each unit and, of course, the number and weight of freight cars. At low speeds, a commuter train may accelerate at 1.5 miles per hour (mph) per second; a fast freight train may accelerate at 0.3 mph per second. As speed increases, the acceleration rate decreases. A freight train with 4.0 horsepower per ton can accelerate at only about 0.1 mph per second at 70 mph.

The braking system used on trains is the air brake that provides adequate uninterrupted pressure from car to car. The single air hose at the end of each car is manually connected to its neighbor, then the brake system is charged. When braking is required, the pressure in the brake pipe leading back through the train is reduced. This causes the valve on each car to use air from the auxiliary reservoir to build pressure in the brake cylinder, thus applying the brakes. For an emergency application, the brake valve opens the brake pipe to atmospheric pressure and the resulting rapid rate of brake pipe pressure reduction causes the car valves to dump the contents of both auxiliary and emergency reservoirs into the brake cylinder.

Braking distances are dependent on many factors that vary for each train, such as the number and horsepower rating of locomotives; number and weight of cars; adhesion of wheels on rails; speed; and grade. Therefore, the braking distance of a train cannot be stated exactly. An estimate is that a typical 100-car freight train traveling at 60 mph would require more than one mile to stop in emergency braking.

Track

In the United States, railroad track is classified into nine classes based upon maximum allowable operating speed. FRA's Track Safety Standards set maximum train speeds for each class of track, as shown in Table B-5 and specified in FRA's regulations at 49 CFR 213.9 and 213.307.

Initially, there were many different track gauges; however, in 1863, President Lincoln designated 4 feet, 8.5 inches as the gauge for the railroad to be built to the Pacific coast. Other railroads then began changing to this gauge.

The rolling resistance that provides many of the technological advantages for railroads as a means of transportation is made possible by the steel wheel rolling on a steel rail. This steel-wheel-to-steel-rail contact involves the transfer of pressures from the rail to a steel plate under the rail (tie plate), which spreads the load over a tie, which spreads the load over ballast (crushed rocks or other materials), which spreads the load to a sub-ballast (usually gravels, cinders, or sand), which spreads the load to the subgrade consisting of either the native soil below or some superior material obtained off site.

Table B-5. Maximum Train Speeds by Class of Track³

Class of track	Freight	Passenger
Class 1	10 mph	15 mph
Class 2	25 mph	30 mph
Class 3	40 mph	60 mph
Class 4	60 mph	80 mph
Class 5	80 mph	90 mph
Class 6	110 mph	110 mph
Class 7	125 mph	125 mph
Class 8	160 mph	160 mph
Class 94	220 mph	220 mph

³ Trains operating at Class 6-9 speeds must be qualified in accordance with 49 CFR sections 213.329 and 213.345. There are additional requirements for freight trains and trains operating at or above 125 mph, as provided in 49 CFR 213.307(a).

⁴ Federal Register Volume 78, Issue 49 (March 13, 2013). https://www.govinfo.gov/app/details/FR-2013-03-13/2013-04679.

Rail is rolled from high-quality steel. Rail being rolled today weighs from 115 to 140 pounds per yard and is 6 to 8 inches high. Currently, the standard rail length is 78 feet. In track, these rails are held together by bolted joint bars or are welded end-to-end in long strings. Bolted joints are, however, less rigid than the rest of the rail so that the rail ends wear more rapidly. Continuously welded rail is often used today, particularly on mainline tracks. Rail is welded into lengths of about 1,500 feet and taken to the point of installation. The remaining joints can be eliminated by field welding in place.

The steel rails are spiked to ties typically made of wood with preservative impregnated to prevent decay. The ties hold the rails to gauge, support the rails, distribute the load to the ballast, and provide flexibility to cushion impacts of the wheels on the rail. Pre-stressed concrete ties have come into greater use on railroads in recent years.

Spikes or other rail fasteners are used to fix the rail to the ties for the primary purpose of preventing the rail from shifting sideways. Because rail tends to move lengthwise, rail anchors can be used, particularly on heavy-duty track.

Ballast is used to hold the ties in place, to prevent lateral deflections, and to spread out the load. Ballast should be able to resist degradation from the effects of tie motion that generates "fines" that may "cement" into an impervious mass. FRA regulations (49 CFR 213.103) require that ballast provide good drainage, which is especially important for the strength of the subgrade and prevents mud from working its way up to contaminate the ballast.

Railway track is normally maintained by track gangs (small groups of maintenance-of-way employees) for small scale repairs or by sophisticated, high production, mechanized equipment for large scale projects. As an example, track surface is maintained by tamping machines that raise the track and compact the ballast under the ties. In this process, it is often necessary to raise the track a few inches. The best track stability will occur if this raise can continue through the crossing area instead of leaving a dip in the track. Lowering track is a very costly operation and can lead to subgrade instability problems.

Similar to highways, railroad track is classified into several categories dependent on its utilization in terms of traffic flow. Main tracks are used for through train movements between and through stations and terminals. Branch lines typically carry freight from its origin to the mainline on which it moves to its destination or to another branch line to its destination. Passing tracks, normally called sidings, are used for meeting and passing trains. Side tracks and industrial tracks are generally used to store cars and to load or unload them. Table B-6 provides a tabulation indicating the number of tracks present on various categories of track.

Table B-6. Public At-Grade Crossings by Type of Track, 2017

No. of Tracks	Type of Track
	Main	Siding	Yard	Transit	Industry
0	14,825	80,152	79,972	85,831	77,313
1	102,963	7,710	4,911	110	8,454
2	10,441	924	1,119	130	889
3	543	177	330	0	149
4	61	47	146	1	34
5	12	11	67	0	15
> 5	28	8	60	0	29
Total	128,873	89,029	86,605	86,072	86,883

Source: Unpublished data from Federal Railroad Administration.⁵

⁵ Updated data can be found on the FRA's Office of Safety Analysis website (also known as safety data) at https://safetydata.fra.dot.gov