Oil and gas executive Lynn Lim used to spend up to four hours driving to her workplace in the heart of Kuala Lumpur from her home in the Subang Jaya suburb, as houses in the capital are too pricey.

But a much-delayed extension to the Light Rail Transit (LRT) system reached her doorstep in June last year, shrinking her commute time to 1½ hours.

Ms Lim, 34, now anticipates the full operation, in July, of Malaysia's first Mass Rapid Transit (MRT) line that greatly expands the rail network within Greater Kuala Lumpur.

"In a year, I'll go from having no train option to being able to go to work in KL and work out at the club in Damansara," she said.

"All these years of seeing others using the LRT, I felt left out by the government. It's good to finally be part of Najib's plans."

Last week's launch of the MRT is a huge landmark for Malaysian Prime Minister Najib Razak. After nearly eight years in power, he sees the first of his many mega-projects finally up and running.

"It wasn't easy because nobody planned for a rail corridor in the Klang Valley," a top MRT executive told The Straits Times, referring to protests from those affected by construction works and land acquisition. "It's a huge gamble, but a necessary one."

The initial phase of the first MRT line runs through an upper middle-class segment of the increasingly congested Klang Valley - an older name for the Greater KL region, which includes the suburbs in Selangor surrounding Kuala Lumpur.

This demographic has mostly turned its back on Mr Najib's Umno-led Barisan Nasional government, which is at its weakest point since the 2013 general election.

The MRT line, which will intersect with other train systems, will be Mr Najib's only mega-project to be completed before nationwide polls - due in August next year, but generally expected this year - are called.

"It is a question of leadership," ISEAS - Yusof Ishak Institute deputy director Ooi Kee Beng told The Straits Times. "A national leader needs to formulate, publicise and remedy difficult problems - and of course, in many senses, these are all inherited from past administrations. So having something to show is important, but winning the trust of the public is a bigger issue."

While Tun Dr Mahathir Mohamad is credited with modernising Malaysia - delivering the iconic Petronas Towers, a world-class international airport and highways filled with national cars - Mr Najib is laying down the tracks of a rail legacy.

It was Dr Mahathir who oversaw the first LRT lines, the KTM Komuter inter-city network, the Express Rail Link connecting Kuala Lumpur to the Sepang airport and the KL Monorail.

But these projects were completed in the last third of his 22-year reign to solve the problem of over-reliance on road transport that was caused by the cheap national cars, Proton and Perodua, promoted by Dr Mahathir, critics say.

At the launch ceremony of the LRT network's expansion last July, Mr Najib attacked his mentor-turned-political nemesis. "One of the challenges we face is that of our transport system and this is because my predecessor, who ruled for 22 years, did not pay attention to public transport," he said.

"And because of that, we face under-investment in the sector and an unintegrated system that was owned by many parties, rendering the transport system unable to support the needs of a town and resulting in massive traffic jams."

Mr Najib launched the MRT just three days after Malaysia and Singapore inked an official agreement to build the 350km high-speed rail linking the two countries.

Although he inherited the LRT extension projects and the national railway electrification projects, these were billed to the government during his time. All told, the Najib administration is betting more than RM200 billion (S$64.5 billion) - about an entire year's fiscal revenue - on rail being the solution to Malaysia's transport woes.

Besides two of the three MRT planned lines racking up a bill of more than RM60 billion, there is the controversial East Coast Rail Link that ties the Klang Valley to the Malaysian peninsula's north-east at a projected cost of RM55 billion. Second Finance Minister Johari Abdul Ghani also said last July that he expected high-speed rail construction costs to reach about RM50 billion.

Adding to Mr Najib's rail portfolio may be Malaysia's shortest railway line - the rapid train system. Though details remain sketchy, it will include an extension of Singapore's upcoming Thomson-East Coast Line into Johor Baru.

But to critics, spending huge sums on infrastructure is not enough. Transport advocacy group Transit said that "the government seems to be more interested in spending money than making hard choices about transport".

"The problem is that, until recently, we have not made parallel investments in bus transport and regulatory improvements," Transit spokesman Moaz Ahmad told The Straits Times.

Having staked so much on laying tracks all over the country, Mr Najib will need to ensure the LRT and the MRT significantly improve commuting around Kuala Lumpur, as a showcase of what his leadership could bring the country.

"Umno is seen to be too much on the defensive and too concerned with staying in power to consider national economy-building in a studied and efficient manner," said Dr Ooi. "If not overcome, this dilemma will see Umno lose power sooner or later."