Alpha 9, better known as A9, is described in military terms as the "Main Supply Route" to the troubled Jaffna peninsula.
But even in civil terms, it is the main link and the shortest link between the Sinhala-speaking South Sri Lanka and the heartland of the Tamils, the Jaffna peninsula.
The road passes through a vast area called Wanni, controlled by the LTTE. It touches the LTTE's political headquarters at Kilinochchi.
The road has two highly guarded entry/exit points - at Omanthai, just north of Vavuniya at the southern end, and at Muhamalai, just south of Chavakacheri at the northern end.
The LTTE took over the Wanni area between Jaffna and Vavuniya after the Indian Peace Keeping Force (IPKF) left in 1990, and used it as a refuge when Jaffna fell to the Sri Lankan army in 1995.
During the ding dong battle over the Wanni and the road, between 1994 and 2002, the A9 remained closed.
But with the beginning of the peace process in February 2002, the road was opened.
The LTTE agreed to open it because it was unofficially allowed to collect taxes, road tolls and customs durties from the users of the highway.
Estimates vary, but the Ministry of Defense says that collections range between SLRs 200 million and SLRs 300 million ($2.8 million) per month.
However, the recent series of military operations, which began in late April, escalated to a point in August when the LTTE made a bold bid to crash into Jaffna through Muhalamai.
The bid failed miserably, and the government used it as an excuse to close the A9 at the northern end.
With Jaffna thus cut off, traffic ceased, and the LTTE's revenue touched rock bottom. Banned in the European Union and under FBI pressure in the US, the LTTE was chocking financially. The need to get the road became critical.
The government knew that the LTTE's shoe was pinching. It said that it would use only the sea route to send essential supplies to the 600,000 people of Jaffna.
The LTTE refused to assure safe passage, but the government was undeterred, though the supplies sent by ship were never adequate.
The fact that only a fourth of the requirement of the civilians of Jaffna was being met, and that the people were on the verge of starvation, helped the LTTE build a strong case against the government on humanitarian grounds.
But despite diplomatic pressure from Norway and the West, the Rajapaksa government decided to stick to its position that an open A9 would only help fill the war chest of the LTTE and pose a major threat to the government's position in Jaffna.