ON March 28 the mayor of Budapest Mr István Tarlós and Hungary's prime minister Mr Viktor Orbán opened Budapest's fourth metro line. Line 4, which is also now known as the green line, is 7.34km long and has 10 stations including the termini at Kelenföld vasútállomás and Keleti pályaudvar, two existing Hungarian State Railways (MÁV) stations.

The opening was an event over 40 years in the making. Plans for Line 4 date from 1972 and the line was originally intended to connect Budaörs with the Rákospalota district. However, only the first phase was planned in detail due to ever rising costs, something which would continue to affect the project as it struggled to get off the ground.

In 1992, an international call for tenders was made for a 5.4km-long line from Kelenföld pályaudvar to Kálvin tér but this was cancelled two years later. An estimate from 1996 put the cost for construction of the line at Forints 132bn ($US 598m), and by May 2003 the plan was extended to Keleti at a revised cost of Forints 195bn. The Hungarian government and the City of Budapest finally signed a contract to build the line from Kelenföld to Keleti station that year, with the government expected to cover 70% of the costs. Construction subsequently began in December 2004 and boring of the dual-bore tunnels, each with an internal diameter of 5.2m, began in early 2007 and was completed in July 2010.

However, with costs ballooning, the project almost ground to a halt at this point after the government refused to provide further investment. A period of contract renegotiation ensued, which resulted in further delays to the project and with the global economic recession beginning to hit hard, dissenters who claimed that the new line was unnecessary, were gaining support.

Indeed arguments against centred on the fact that a former bus link between the terminal stations of Line 4 only took a little longer than the metro's 13-minute journey time. The addition of dedicated bus lanes which improved services in the city also added weight to claims that the metro was an unnecessary expense.

budapestFollowing a change in national government and in the city's administration in 2010, a decision had to be made of whether to proceed, or to cancel Line 4 and potentially lose the money that had been invested up to this point. With city-centre traffic remaining intense, and central bus routes now at capacity, sense prevailed, and following a successful renegotiation of contracts to reduce overall costs, work continued to fit out the tunnels and complete the project by March 2014, just before the next national election.

The total cost of the project eventually came in at Forints 452.5bn, including Forints 67.5bn in contingencies for possible future compensation and penalties to contractors. Of the total cost, Forints 180.8bn was financed by the EU's Cohesion Fund, Forints 193.7bn from the Hungarian government, and Forints 78bn by the City of Budapest, of which Forints 15bn was from an EIB bankloan.

Line 4 is now served by a fleet of 15 four-car Alstom Metropolis metro trains, which operate at a maximum speed of 80km/h. Initially the trains are fitted with drivers' cabs at either end, but these will be removed when the manual operation test period concludes and the line switches to automatic operation, possibly in October.

Siemens supplied its Trainguard MT communications-based train control (CBTC) system for the line which supports automation. Trainguard MT's moving block signalling can offer headways of 90 seconds, although the minimum headways on Line 4 are 2min 45s during peak periods, and 5-10 minutes at other times. The Forints 39bn contract with Siemens also included the supply of CCTV, telecommunications and fire alarm systems, as well as the third rail electrification system, which mimics that used on lines 2 and 3.

Instead of platform screen doors, a key feature of most automated metros, Line 4 utilises a radar system which monitors the track. Sensors are positioned 15cm apart, and if more than one is activated, trains are automatically stopped. Lights in the platform floor show the safety line and blink when a train is approaching, with orange lights showing that the incoming train is heading towards Keleti, and purple lights indicating that the train is bound for Kelenföld. There are also pedestrian walkways throughout the tunnels for straightforward evacuation.

Despite the entire line being underground, natural light has been used wherever possible with most of the stations being relatively close to the surface, apart from around the crossing of the Danube where the tunnels are 33m deep. For example at Rákóczi tér station a surface mirror system reflects sunlight into the station through two vertical tubes.

So what do the people living or working in Budapest think of Line 4, the city's largest single infrastructure investment in the past 25 years? As a means of transport it was integrated into the life of the city very quickly. And while it is still too early to judge how the service will change long-term travelling habits, building the line has changed the appearance of many important city locations and in terms of its early use it is living up to, if not exceeding expectations, with 100,000 passengers a day now using the service.

Following the completion of construction and the successful start of operations on Line 4, attention has shifted to proposed extensions. However, Tarlós was quick to announce that a four-station cut-and-cover extension from Keleti towards Bosnyák tér is indefinitely postponed as there is no financial support to build it. He added that any future extension would more than likely take place at the western terminus to Budaörs, but there are no immediate plans to carry out this project, while the European Commission has been reluctant to discuss supporting it.

Most traffic planners are of the opinion that a four-station eastern extension will eventually be required, but have suggested an initial link to Gazdagrét as a realistic first stage for the western project. However, Budapest Transport Centre (BKK), which operates metro, bus and tram services in Budapest, appears to favour investments in its surface routes including filling in missing links and adding circular tram lines over further metro construction. These are intended to ease the strain on the city centre's services, decreasing the immediate need to further extend Line 4. EU funding also appears to be more readily available to support projects to upgrade the existing tram network, with changes in the funding application process meaning that BKK could potentially secure up to 99% of the funds required from the EU.

While Brussels and Budapest appear to be against extending Line 4, this is not the only metro extension under consideration.

An extension of the cut-and-cover underground Line 1 a few stops northeast from Mexikói út in parallel with the M3 highway is a relatively straightforward project. Another much-discussed plan is the creation of a north-south axis that will link the suburban HÉV lines leading to Szentendre and Csepel. This would require a 5km underground link from Batthyány tér to Boráros tér that would also need to cross under the Danube.

An alternative would be to run the HÉV trains along the tram tracks on the surface, but this would mean using tram lines 4 and 6 which avoid the centre of the city and already operate a service every minute during peak hours. Furthermore, the loading gauge is restrictive with the Siemens Combino Supra trams that currently use the line only 2.4m wide. Using tram Line 2 along the Danube is also not a realistic option as stations are not long enough to accommodate more than one tram while the line uses a 500m-long viaduct built in 1900 that would need replacing. Development in the area is also inhibited by its status as a Unesco World Heritage site.

While the debate over what is next for Budapest's metro and tram network is set to continue, one thing is clear: the city is simply too large to be able to serve its busiest entrance point with a metro line that terminates at Kelenföld and the city centre. The concept for extending this important route is clearly there, but unfortunately the finances and political desire to undertake the project is distinctly absent.

By allowing surface routes to feed into Line 4 and by failing to serve Bosnyák tér in the first phase, many commuters from the more distant suburbs will be forced to make more than one transfer during their journeys into Budapest for decades to come. On the other hand, as the line is only designed for four-car trains, only a limited number of people can use the service. As a result serving highly-populated areas may quickly lead to overcrowding.

Was it right to build Line 4 to serve very high levels of peak-hour traffic with lower use during the day? Or should stations have been built to accommodate five-car trains? Changes in traffic trends will certainly need close observation until the finances for an extension become available so the right choices can be made in future projects. In the meantime, Line 4 will continue to offer added convenience to those who have embraced the service in its first few months of operation.