Light rail, loosely defined as a rapid-transit style urban rail transport network with lower speeds and capacity than heavy rail, is an enticing solution for a growing number of cities around the world.
With government transport budgets more strained than ever, global carbon emissions running rampant and many city centres becoming unbearably clogged, this lighter rapid transit option is attractive on several levels.
The argument for implementing modern light rail systems for urban transport is a convincing one. Environmentally, light rail and tram networks hold significant advantages over heavy rail and bus systems as most light rail vehicles are powered electrically, with no emissions at the point of use and a more efficient use of energy.
Light rail's pros and cons
Light rail scores highly in other areas, too. High passenger capacity and low overheads makes for comparatively inexpensive operating costs, and unlike heavy rail systems, light rail vehicles can integrate with existing transport infrastructure, minimising expense by allowing tracks to be laid alongside existing streets or road reserves.
Quieter operation and generally more appealing aesthetics also often makes light rail more palatable to a city's residents than its transport alternatives.
Factors such as these are the reason behind the Obama administration's U-turn on light rail in the US in 2010, making it easier for light rail projects to secure funding in cities across the country.
"We want to base our decisions on how much transit helps the environment, how much it improves development opportunities and how it makes our communities better places to live," said US Secretary of Transportation Ray LaHood during the announcement last year.
For US Representative Earl Blumenauer, who saw his native Portland's Streetcar light rail system unable to expand under the Bush administration's strict regulations, this decision is a major economic and ecological boon. "This means quicker and better funding for streetcars, light rail and bus projects that improve transportation, revive local economies and reduce global warming pollution," he said.
Implementing a major new light rail system in a city is not a risk-free venture, however. Initial construction costs can vary wildly depending on local conditions, such as the need for tunnelling in poor soil conditions, as well as underground or elevated sections.
While some light rail transit (LRT) systems can cost as little as $15 million a mile, difficult conditions can inflate that cost by ten times or more.
Seattle's Link light rail system, which has two lines operational and four planned for the future, has been the US' most expensive LRT project, reportedly costing approximately $179 million a mile.
Building a light rail system in a heavily populated area can also pose delicate social challenges.
Here we look into three high-profile light rail projects, each at a different stage of development and dealing with different challenges, to find out about light rail development in the modern age.
Ride the tide: Norfolk's light rail 'proof of concept'
With a population of around 250,000, Norfolk in the US state of Virginia is set to become the smallest city in the country to be served by a light rail system, dubbed The Tide.
As such, it could be seen as the US' proof of concept for light rail in cities with smaller populations, as conventional wisdom dictates light rail systems make back their development costs through large passenger numbers.
Due to begin operations on 19 August this year, the project certainly didn't get off to a strong start, with planning complications and high initial cost estimates seeing it scaled back from an 18-mile link between the city centre and Virginia Beach to a 7.4-mile line serving Norfolk only.
The project has also been plagued with cost overruns and delays. The Tide's total cost eventually ran to $338.3 million, more than $100 million over budget, and the line's opening has been delayed several times since its proposed launch of January 2010.
It appears that many of the project's issues stemmed from unrealistic cost expectations, as the original budget was simply not enough to build a sufficiently advanced system. The increase in cost and project time allowed for extensive testing and the installation of a safety signal system and communication system, features that were not originally planned.
But the system is now operational and ready to take its first passengers through the line's 11 stations, carried by nine 95ft electric cars powered by overhead catenary wires; daily use is expected to start at 2,900 people and rise to 7,000 by 2030.
If the line prompts private investment and economic growth in Norfolk, as it is expected to do, it seems only a matter of time before other small US cities start making plans of their own.
Ottawa: betting big on LRT
Over the border to the north, Canadian capital Ottawa is in the very early stages of its own LRT, the latest in an impressive line-up of light rail projects in the country being funded in Vancouver, Calgary and Toronto, among others.
Ottawa's C$2.1bn light rail plans are intended to relieve rush-hour congestion in the bus-reliant city centre. The project, which will implement an east-west, 12.5-kilometre, 13-station light rail line with an underground tunnel for a downtown section, was approved by city councillors on 14 July.
Like Norfolk's Tide light rail project, Ottawa is also seeking to control costs for its LRT system to keep the project at its C$2.1bn budget. Cost-cutting measures include shorter platforms and simplified facilities at stations and moving Campus Station from underground to the surface, but most significant is the decision to move the line's underground section to beneath Queen Street, allowing for a shallower tunnel (15-16 metres rather than 39-40 metres) that will reportedly reduce total tunnelling costs from C$793m to C$493m.
This will primarily be achieved by employing the 'cut and cover' method, a more basic, inexpensive but potentially much more disruptive shallow tunnelling technique.
Even though the project is at its very earliest stages - after the approval, contractors will be awarded in 2012, with construction set to run from 2013 to 2018 - one particular challenge of inner-city rail development is already becoming apparent.
As the line is being built through some of the city's most treasured downtown areas, observers are concerned about the line's effect on important heritage sites. For example, top staff at the city's National Arts Centre (NAC) and Arts Court are concerned noise and vibration from the line could disrupt performances.
"Anything that relates to noise or vibration would disrupt the performances inside the building," NAC spokesperson Carl Martin told CBC News. "In our case the building exists already so you can't go back and isolate the building. There are engineering issues that are very complex."
Jerusalem's controversial light rail project
With construction started in 2002 and completed in 2010, Jerusalem's new light rail line should by rights be fully operational and carrying passengers by now.
The $1.2bn project is expected to offer a greener alternative to the city's existing carbon-heavy public transport and stimulate economic growth by boosting tourism to the city's holy sites.
But a host of technical problems combined with complex political tensions and poor management have caused an endless stream of delays for the project. For many in East Jerusalem, the predominantly Palestinian area of the city that was annexed by Israel after the 1967 Six-Day War, the upcoming line represents a new avenue of Israeli settlement expansion.
This criticism has plagued the project from the start, leading to European rail companies Alstom (which provided the vehicles for the line) and Veolia selling their shares in CityPass, the consortium responsible for building and operating the line.
This tension, amplified by security concerns for the project, has seen the project delayed countless times, pushed back from an original launch date of 2006 to August this year, a date that could possibly be delayed again, according to city officials.
Technical problems abound on the project as well, with synchronisation between the city's traffic lights and the new trains a particular problem. Although the line, which runs through 23 stations from Air Force Street to Mount Herzl, is due to come online on 19 August, total journey times have been revised from 40 minutes to 80 minutes as the trains will have no right-of-way at traffic lights. The original journey times will not be achieved until October at the earliest, when synchronisation is due to be completed.
Nevertheless, Jerusalem Mayor Nir Barkat remains optimistic about the line's potential to bring the city together. "This is an effective way to create a network which enables all residents, regardless of their religion, to move from any source to any destination," he told Reuters this month.
Jerusalem Transport Management Team strategic advisor Shmuel Algrabli also believes the pain of the project's development will be outweighed by its benefits once operational. "It's been a long, difficult birth," he said. "But we are almost there."