Here are answers to some of the most frequently asked questions about light rail:
Why this FAQ?
Light rail could be one of the most effective tools for protecting and helping restore the environment.
What is light rail?
Light rail is a form of urban rail passenger transportation that has evolved from trams (also referred to as streetcars or trolleys). It has characteristics intermediate between those of trams and rapid transit, including generally higher speeds and greater capacity than conventional trams and lower construction costs, greater routing flexibility and, often, increased user convenience as compared with rapid transit.
Light rail vehicles typically have larger passenger capacities than trams, mainly because of a greater length, but also in some cases because they are wider. They mostly operate on dedicated rights-of-way, including adjacent to streets, in tunnels and on elevated structures, thereby minimizing interference from road traffic, but they can also operate on tracks embedded in streets, in transit malls and even on conventional railroad tracks. Most are powered by electricity supplied through overhead wires, although some use other technologies.
Why is it called "light rail"?
The term light rail derives from the much older, and somewhat more descriptive, term light railway, which is a form of rail transportation that uses lighter weight vehicles and has lighter weight rails than most conventional railroads. It was coined in the United States in the 1970's to promote a new generation of streetcar systems that were emerging at that time in both Europe and the U.S. The existing terms streetcar and tram were widely associated by the public with slow, noisy and "old fashioned" rail vehicles that both frequently got stuck in traffic and were regarded as impeding traffic. An alternative term for light rail favored by some is second generation tramway.
What is the difference between light rail and trams or streetcars?
A main difference is that, whereas trams (or streetcars) mainly operate on tracks embedded in streets together with automobiles and other road traffic, light rail tracks are usually mostly located on exclusive rights of way, which are often strips of land adjacent to streets or in the medians of streets. They can also be located elsewhere at surface level, including in streets with other traffic or in transit malls for parts of their routes, and in some cases they utilize sections of track belonging to existing tram lines. As with rapid transit, they can additionally operate on elevated structures or underground and they can even operate over conventional heavy rail tracks.
The predominantly off-street operation of light rail vehicles allows them to travel at substantially faster speeds than most first-generation trams. Also contributing to the higher speed is the frequent use of signal priority at intersections, both where the light rail vehicles operate in streets and where they operate on exclusive rights of way. Overall speed typically is also enhanced by a greater distance between stops than for trams as well as multiple doors that allow faster boarding and exiting by riders.
However, the distinction between streetcars and light rail is not always clear. One reason is that some streetcar systems have lines that have light rail characteristics. Also, especially in Europe, many older streetcar systems are in the process of being gradually upgraded to light rail standards. Thus, it is not uncommon to see modern light rail vehicles on some of the same tracks as older streetcars that have been operating there for many decades — or even a century or more.
Do people really want to ride light rail? Don't they usually prefer their own automobiles?
There is a variety of reasons that even some people who have access to automobiles choose to ride light rail and other public transportation. One is that public transportation can be cheaper, especially when the full costs of automobile use (including gasoline, parking, depreciation, maintenance and insurance) are taken into consideration. A second is that in some cases it can be faster. A third is that it can allow passengers to do other things during the journey, including working, reading and sleeping. A fourth is that it can avoid the problem of searching for a parking place. In addition, some people prefer transit because they are concerned about the environment.
In what ways is light rail better than rapid transit?
Its greater flexibility with regard to routing, including the ability to operate in or adjacent to streets as well as in transit malls rather than always requiring tunnels and elevated structures, gives light rail a much lower construction cost than rapid transit. Such surface operation is convenient for users because it allows them to board and alight vehicles without having to descend into tunnels or ascend up to elevated structures.
When is rapid transit superior to light rail?
Rapid transit can typically provide greater speed and greater passenger capacity than light rail. The former is mainly because it always operates on an exclusive right of way rather than partially in or adjacent to streets, and the latter in large part a result of the higher speeds. Because of its much higher construction cost, this mode is best suited for heavily traveled routes in very large cities.
Aren't monorails superior to light rail?
Monorails have long been viewed by many to be the transportation of the future. Although a number of monorail lines have been constructed since the first experimental one opened nearly two centuries ago in England, they still account for only a tiny minority of urban transportation systems because of several inherent problems.
Particularly important is their lack of flexibility because the track switches are much more complex and far more costly to install than light rail switches, thereby limiting their use to routes with few if any branch lines. Another problem is that they cannot operate at ground level, including in streets, roadway medians and transit malls, in contrast to light rail, thus requiring the construction of costly elevated structures and making them less convenient for boarding. The requirement for elevated structures also makes monorails unsuitable for use through most historic areas.
Construction costs for monorail systems are not necessarily lower than for light rail systems. In addition, maintenance costs can be higher due to their proprietary technology and specialized components, which often need to be custom produced. Light rail systems, in contrast, generally use standardized parts for the vehicles and tracks that are produced in large volumes and are available from a variety of competing sources.
Aren't buses better than light rail because they are more flexible?
There are many differences between bus and light rail transportation. Each has its advantages and disadvantages, and which is best for a particular situation depends on a number of factors.
In general, buses have the important advantage that new routes can be implemented very quickly, much faster than for new light rail lines and at much less cost. Likewise, routes can be modified quickly and at minimal cost. However, these advantages diminish for enhanced bus service, and especially for bus rapid transit.
Buses also have major disadvantages as compared with light rail. One is that they are generally much less energy efficient because much more energy is required to push an equal weight on rubber tires on a concrete or asphalt roadway as compared with steel wheels on steel rails.
Also, light rail systems produce much less air pollution and greenhouse gas emissions than internal combustion engine buses because they are almost always electrically powered, and increasingly that power is obtained from non-polluting energy sources. Although electrically powered buses are becoming increasingly common, they have other disadvantages, including greater power consumption and increased roadway wear due to their greater weight because of the heavy batteries they carry.
Another disadvantage of buses is they have much less capacity than light rail vehicles, with maximums of about 60 passengers for standard buses, 120 for articulated buses and 160 for double deck buses, including standing passengers. Maximums for light rail are about 220 for standard vehicles or well over a thousand for multi-car light rail trains.
In addition, conventional bus services are typically substantially slower due to traffic congestion, slower passenger entry and exiting, and slower acceleration and deceleration. Moreover, they can be less comfortable for riders because of their more cramped interiors, jerkier movement and greater noise.
Why do people prefer riding light rail to riding buses?
Light rail systems can provide several important advantages over buses for passengers. One is that they can be faster when they use exclusive rights of way and have intersection signal priority. A second is that they are generally more comfortable because the rides are typically smoother and quieter and the vehicles are more spacious.
Is light rail superior to bus rapid transit?
True bus rapid transit (BRT) is similar to conventional rapid transit, including its use exclusive rights of way and multi-door boarding and exiting. However, it differs mainly in that the vehicles have rubber tires that run on paved surfaces rather than steel wheels on steel rails. BRT systems can provide a much faster and more reliable service than conventional bus systems because they do not get stuck in traffic, do not have to wait for road traffic signals, and have faster boarding and exiting.
The biggest advantages of BRT as compared with light rail include a lower system construction cost and faster implementation. It can additionally offer a greater flexibility of operation if the buses used are are capable of also operating on conventional streets. However, buses on some true BRT systems are not optimized for running on ordinary streets because of their larger size.
A main advantage of light rail as compared with BRT is a much greater passenger capacity. This is because the vehicles can be larger and connected together to form trains. Other advantages include lower maintenance costs, longer vehicle lifespans, greater passenger comfort, lower energy consumption, and less environmental harm including from dust and runoff from the brakes and the tires on the paved surfaces.
Why were most tram systems scrapped during the middle of the twentieth century?
A major reason was the emergence of an attitude that trams were "obsolete" because buses were more flexible and had a lower cost of operation. Many systems also suffered from substantial deferred maintenance due to the Great Depression and then World War II and would have required very large expenditures to restore them. Also, powerful business interests, particularly in the U.S. and especially automobile manufacturers and tire producers, pushed for the scrapping of rail systems in order to promote automobile sales.
Why did some cities retain their first generation trams despite the prevailing post World War II trend to scrap them?
Some cities survived this great scrapping because of differences in economic conditions, in attitudes regarding urban planning and economic efficiency, in commercial pressures and in the physical characteristics of systems. For example, many systems in Central and Eastern Europe survived largely because of the strong desire to preserve their traditional high-density cities and architectural heritage, the expense or difficulty of obtaining gasoline, and the absence of strong commercial pressure to scrap their systems, in contrast to the situation in the U.S.
But aren't trams an old, outdated technology?
No, quite the contrary. Light rail technology has continued to advance in numerous ways, resulting in enhanced passenger convenience and comfort, higher speeds, reduced operating costs and greater safety. For example, fully low-floor vehicles have been developed and are now becoming commonplace, thereby making entry and exit easier, faster and safer. This is particularly important for persons with limited mobility as well as for passengers with wheelchairs, baby carriages, bicycles, etc.
Advances in electronic hardware and software have allowed improved real time information for system managers and passengers as well as automated obstacle detection and even semi-automated operation. Also, various technologies have been developed to eliminate the need for overhead wires.
What is the "tram renaissance"?
After decades of scrapping existing tram systems throughout much of the world, a dramatic reversal of attitudes emerged beginning in the 1980s that has resulted in a boom in the construction of new light rail systems and the expansion and upgrading of existing light rail and tram systems worldwide.
This occurred is a result of ever-increasing traffic congestion and growing awareness about the harmful effects of air pollution. It is also because city planners and environmental experts have increasingly recognized that this form of urban transportation can, with good planning, be far superior to ever more cars, ever wider freeways, and ever more parking lots for increasing mobility, minimizing energy consumption, reducing air pollution, and generally improving the quality of life.
What are some specific examples of the tram renaissance?
One of the most outstanding examples is that of France. That country replaced most of its numerous tram systems with buses beginning in the 1930s so that eventually just three truncated lines remained, and they remained only because they would have been difficult to replace with buses. Typical reasons given for this swift dismantling were that trams were "obsolete," that they were obstacles to automobile traffic, and that buses allow a lower cost and more flexible operation.
However, it gradually became clear that this approach was not working. Traffic became more and more congested, due to the continued increase in the number of automobiles which, in turn, was in part due to the decline in the speed and quality of public transportation.
In 1985 Nantes, a city of about 320,000 in western France, became the first in Europe to restore trams where they had previously been scrapped. The resounding success of this new, second-generation surface rail system has so far resulted in more than 30 French cities of all sizes likewise constructing new tram systems, often in conjunction with creating automobile-free tram malls in central areas, restoring historic building facades, adding street furniture, and making other improvements along the new light rail routes. Still more new systems are being planned in France and many of the new systems are already being expanded.
This pattern is being repeated in many other countries, both in Europe and elsewhere. For example, in the United States, where only about a half dozen light rail or streetcar systems remained, the number of new or expanded systems has soared to more than two dozen and many more are being planned or discussed.
How can the success of the tram renaissance be measured?
This success has been manifested in various ways. Ridership has generally been much greater than for the bus routes that the new light rail lines replaced, and often substantially greater than projections. Local air pollution and traffic congestion have decreased as a result of many trips being taken by light rail instead of by private automobile. And the introduction of light rail has often revitalized nearby neighborhoods and led to much new construction. Another indication of the success is the fact that the number of new and planned light rail lines continues to increase worldwide.
How can light rail help protect the environment?
Light rail systems can contribute greatly to protecting the environment, in addition to offering other important benefits. Most fundamentally, they can provide an excellent alternative to the use of automobiles in many situations. Although automobiles and other road vehicles can be very convenient, their mass production, usage and disposal, together with the vast roadway, energy and other infrastructure they require, has been one of the largest causes of the earth's environmental destruction and one of the top causes of injuries and death.
Decreased automobile use as a result of increasing the availability and use of light rail can reduce greenhouse gases and other harmful emissions. Light rail also facilitates compact urban development, including minimizing land used for roads and parking, and can be an important tool for minimizing sprawl. Compact urban development reduces the distances people need to travel for daily activities, thereby encouraging walking and bicycle riding as practical and pleasant alternatives to driving.
What are the environmental benefits of light rail as compared with buses?
Light rail vehicles are inherently more energy efficient than buses because the energy required to push a weight with steel wheels on steel rails is much less than that for an equal weight on rubber tires. Also, light rail systems produce less pollutants than comparable bus systems both because of this greater energy efficiency and because they use electric power rather than internal combustion engines. Although buses are increasingly using batteries, the batteries are very heavy, thus adding to bus energy consumption.
Another way in which light rail can be superior to buses with regard to protecting the environment is that it attracts more riders than buses because of its generally faster and more comfortable rides. Thus, by further inducing a shift away from automobile travel, it can be more effective in promoting dense, walkable neighborhoods as an alternative to more sprawl.
Are there any other benefits of light rail beyond helping to protect the environment?
Yes, there are considerable additional benefits. One is that it can increase mobility, and thus improve the quality of life, by providing a speedy and quality alternative to automobile and bus transportation. This is important for people who cannot drive due to age, disability, financial situation, preferences etc. as well as those who could drive but don't like being stuck in traffic congestion or would rather read or sleep while making their trip.
A second benefit is that it can reduce the large expenditures for new and enlarged roads that would otherwise be necessary to accommodate more vehicular traffic. In addition, it can help promote urban density and walkability, including by reducing the use of land for parking lots.
Still another non-environmental benefit of light rail is that it can reduce the share of road transport in total local transportation and thus reduce injuries and death from road traffic accidents. In many countries, including the U.S., traffic accidents are a top cause of premature death and disability and the total number of deaths from automobile use greatly exceeds the total number of deaths from wars.
Constructing light rail systems can be very costly. Wouldn't it be better to spend the funds on expanding road capacity instead because most people choose to travel by automobile?
Not necessarily. A major reason is that widening existing roads, building new ones and adding more parking lots to increase capacity will almost inevitably result in increased environmental damage, including more air pollution and more greenhouse gas emissions.
Another is that such expenditures often do little in the long run to reduce traffic congestion and increase speeds because of induced demand.
Moreover, it should be kept in mind that some of the preponderance of automobile use in urban areas may be due not to any inherent preference by drivers for that mode but rather to the fact that they have little choice because there has been relatively little investment in alternative modes, particularly rail, for many decades.
Can light rail be profitable?
It is difficult for light rail systems to be profitable in the conventional monetary sense that revenue received from passengers covers all costs, including those of both construction and operation. However, such profitability is not useful as the sole measure of the value of a light rail system, just as the value of trees, sidewalks, fire departments and public health services can not be measured in terms of monetary profitability. A much more useful way to evaluate an existing or potential system is by using cost-benefit analysis.
This is not to say that traditional consideration of monetary profitability should be completely ignored. But, rather, it should be used as just one measure of efficiency, including for making comparisons with other systems, and for evaluating what can be done to minimize financial losses without greatly reducing the other, non-monetary benefits of the system.
What size cities is light rail most suitable for?
Although light rail is often thought to be best suited for cities with at least 100,000 inhabitants, it can also be suitable for smaller cities in some circumstances. In fact, there are even a few towns with populations of less than 10,000 inhabitants that have short systems.
Several other factors are at least as important as size in determining the suitability of light rail for a city. They include density, the desire to preserve historic areas, concern about the environment, and existing rail infrastructure that could be utilized.
Can light rail also be used to connect cities or towns rather than just operate within single urban areas?
Connecting cities was common in the first decades of the twentieth century with interurbans, which were essentially light rail lines or networks between cities or towns. Many of them also provided local streetcar services within the cities and towns. Some also provided freight services. A number of examples still exist, mainly in Europe.
Can light rail also be used for freight?
In the early twentieth century many light rail systems provided both passenger and freight services. This applied to some conventional streetcar systems but particularly to interurban light rail lines. Even today a few systems still provide freight services. There has been much interest and some experimentation recently, particularly in Europe, regarding the use of existing urban tram networks for some types of freight in order to reduce truck traffic.
Can light rail really reduce traffic congestion?
Not necessarily. Although light rail and rapid transit projects are frequently promoted as a means of reducing traffic congestion, often there is little reduction, especially on major trunk roads. However, this should not be seen as a failure of these projects, but rather it is a result of the inevitable induced demand for road transport as well as of poorly planned or implemented road transportation and land use policies. Also important to keep in mind is the fact that the most important benefits of rail are other than reducing congestion.
Why should vast amounts of money be spent building light rail systems if they cannot reduce traffic congestion.
One reason is that a well-planned light rail system can keep congestion from getting even worse. A second is that it can provide quality transportation for the substantial numbers of people who cannot or do not want to drive automobiles or who do not want to ride slow-moving buses. A third is that, with appropriate land use policies, it can help create dense, walkable neighborhoods and slow the spread of urban sprawl.
How can light rail be used to reduce traffic congestion?
Light rail — or heavy rail or rapid transit — can be most effective in reducing traffic congestion if it is part of a broader transportation and environmental protection strategy. That is, it can help reduce congestion if it provides a higher quality of service, a large part of which is a faster speed, than driving together with measures to reduce road traffic, particularly congestion pricing, but also levying parking taxes and adding transit malls. Road pricing by itself often has little effect on reducing congestion in the absence of good alternative transportation, but a high quality rail system that is not affected by road congestion can provide that alternative.
Why should light rail sometimes operate on streets that are also used by automobiles and other road vehicles?
One reason is that it can greatly reduce construction costs as compared with putting it underground or on elevated structures. Another is that there is often insufficient space to build a separate ground level right of way for light rail in high density urban areas. Also, many light rail lines, particularly in Europe, utilize the tracks of existing first generation tram lines that are located in streets for portions of their trips. Moreover, it can be more convenient for passengers to be able to board and exit at street level. In addition, the greater visibility of light rail vehicles that operate at surface level rather than underground may encourage more people to use them.
The adverse effects of operating light rail in streets can be mitigated or eliminated in several ways. One is by restricting the operation of automobiles and other road vehicles on the tracks. Another is by providing signal priority.
Why do light rail vehicles sometimes also run on conventional railroad tracks?
This is the tram-train concept, a relatively new and rapidly growing type of rail passenger transportation.
What are tram-trains?
Tram-trains are a hybrid form of transportation that combines the characteristics of both trams and conventional railway passenger trains. These vehicles are designed to operate on tramway tracks in city centers and on conventional railway tracks elsewhere. This use of existing rail infrastructure can be much more economical than constructing new light rail lines to outer areas. It can also have the advantage of providing more convenient access to multiple locations in central cities than can the conventional railway stations used by conventional local railway services.
What is being done to upgrade first generation tram systems to light rail standards?
A major part of this upgrading is modifying the track and other infrastructure to allow the safe operation of heavier and faster vehicles as well as to provide smoother rides, reduce noise and accommodate low floor trams. This includes separation from road vehicles where practical and economical by such means as relocating tracks to exclusive grassy strips parallel to roads and by creating transit malls. In addition, signaling and communications systems are being added or upgraded.
At the same time, new vehicles are being added that have greater passenger capacities, faster acceleration and speed, reduced power consumption per passenger, smoother rides and better passenger amenities. Among the most important ways in which passenger convenience and safety is being improved is by utilizing low floor technology. Also important are the addition of advanced fare payment systems and unobtrusive passenger information systems.
What are low floor trams?
Low floor trams are designed to improve accessibility for passengers by eliminating the steps between the vehicle entrances and the passenger cabin. This curb-level access makes it easier for individuals with mobility challenges, such as those with knee injuries or using wheelchairs, or people pushing strollers or having heavy luggage, to board and exit. Another major benefit is higher average travel speeds because of reduced station dwell times. Moreover, both this easier access and the consequent faster speed can encourage more people to use the system.
The major disadvantage of low floors is that maintenance costs for both the trams and the rails can be as much as 20 percent higher than for conventional high-floor tram systems due to the greater complexity of the wheel mechanisms and their greater wear on the rails. However, this is mitigated to some extent because of the less robust track infrastructure required owing to the lighter vehicle weight.
Although low-floor trams were first developed more than a century ago, their use was limited and it wasn't until the 1990s that modern, fully low-floor trams were developed and began to see widespread use. They are now becoming common on systems throughout the world.
What are some of the other amenities being provided by light rail systems?
Light rail systems are being increasingly designed to provide a range of amenities that enhance the passenger experience and attract more riders. In addition to higher speeds, smoother rides and the use of low floor vehicles, they include more payment options, unobtrusive real-time information systems, bicycle facilities, free wifi and enhanced security. Additionally, at some stops they include shelters, seating, restrooms, retail and food options.
How does light rail affect land use patterns?
Light rail can significantly influence land use patterns, particularly by encouraging the construction of high density and walkable neighborhoods near stations as an alternative to distant, automobile-dependent suburbs. It is particularly effective when used together with zoning and other land use policies that encourage higher densities and discourage sprawl.
Are there any tram systems that are powered by renewable energy?
Powering trams by renewable energy is an important new trend. Many systems are partially powered by clean energy and several are fully powered. The Melbourne tram network, the world's biggest, claims to have become fully offset by renewable energy from several large solar farms.
Can electrically powered light rail operate without overhead wires?
Wireless operation is another important trend in light rail technology. Ways in which it is being achieved include the use of a ground-level "third rail" and batteries. The former, which is embedded between the two running rails, is divided into small sections so that only the segments that are directly under the tram are energized, thus making the system safe for pedestrians. Because it is much more expensive to install than overhead wires, it is only being used in limited areas, such as historical districts. Several systems use batteries or high-performance capacitors instead of overhead wiring for parts or all of their routes.
Are there any alternative power sources for light rail?
Diesel and fuel cells are being used on a few systems.
What is being done to reduce the costs of light rail systems?
Various things are being done to minimize the costs of light rail systems without reducing the quality of service. Infrastructure costs can be minimized by locating new lines in exclusive rights of way in street median strips and in transit malls as well as on existing railroad rights of way instead of in expensive tunnels or elevated structures. In addition to being much cheaper and faster to install, such ground level operation can be more convenient for users.
Developing standardized designs for infrastructure and vehicles across multiple systems can minimize construction and operational costs because of economies of scale and by preventing vendor lock-in. Increasing capacity utilization by increasing the number of riders can lower the cost per passenger. Automation is increasingly being used for some operations, such as maintenance, to reduce labor costs and improve operational efficiency, including power consumption.
What are the criteria for determining whether a new transit line or system should be bus, light rail, rapid transit, heavy rail, or some other mode?
The best way is to evaluate each alternative is by using cost-benefit analysis that takes into consideration all factors including construction and operation costs, existing infrastructure, population size and density, possible effects on land use patterns, historic preservation, environmental effects and public health effects. The "other modes" could include bus rapid transit, trackless trolley, monorail, funicular and aerial gondola.
What are the negative externalities of light rail?
The negative externalities can include disruption during construction, visual intrusion of overhead wires, delaying street traffic, removal of traffic lanes, exposure to energized wires such as during adverse weather conditions, stray currents, displacement of residents or businesses due to rising property values near stations, operational noise and accidents.
What is being done to eliminate or reduce these negative externalities?
Disruption during construction can sometimes be minimized through scheduling some construction at night in commercial areas, using special measures to maintain access to local businesses during construction and providing subsidies to affected businesses. Overhead wires in certain segments, especially in historic areas, where they can cause visual intrusion, are often eliminated in new systems. The removal of traffic lanes for use by trams can actually be beneficial because it can reduce air pollution and traffic noise.
What is being done to reduce light rail noise?
Noise and vibration from light rail operations can adversely affect both passengers and the surrounding communities. Those related to the motion of the vehicles on the steel rails are being reduced by the installation of sound and vibration-absorbing materials under the rails, the use of noise barriers, the use of continuously welded rails and improvements to track switches. Regular rail grinding, often by track mounted rail grinding vehicles, can also provide substantial reductions in noise and vibration.
Noise from public information systems in the vehicles and at stops can also be a problem on some systems, especially for riders and nearby residents who are especially sensitive to noise. Ways in which this can be minimized include reducing the number of announcements and keeping the volume low, creating quiet areas in vehicles and at stops, and a greater use of visual displays instead of acoustic announcements.
How can light rail safety be maximized?
Although light rail and other forms of rail are typically much safer than driving, safety can still be a problem. Among the many things that can be done to maximize safety include the use of dedicated rights of way rather than street tracks when practical, installing fencing or other barriers along tracks, use of crossing gates and signals at road intersections, creating public awareness campaigns, and safety training for transit vehicle operators, automobile drivers, bicycle riders and pedestrians.
The use of low floor vehicles can also make a valuable contribution to passenger safety. Vehicle interior design is also important, including plenty of handrails, sufficient seating for handicapped passengers, systems for emergency communication with the vehicle operator, and video monitoring of vehicle interiors and stops.
How many cities have light rail?
There are now approximately 400 systems worldwide, and the number is continuing to increase. More than half of these are in Europe.
What city has the world's largest tram system?
The largest tram system is in Melbourne, Australia, with a total length of roughly 250 kilometers and about 520 trams. This is followed by St. Petersburg, Russia at around 205 kilometers and then Berlin at about 193 kilometers.