Question: How developed is the road based transportation system in Mongolia?
About the article "Mongolia", section "Transportation".

Candidate passages:
The transportation system in Mongolia consists of a network of railways, roads, waterways, and airports. 
GNSS road pricing enables road pricing policies based on time, distance and place (TDP).
TDP road pricing is very much based on the road pricing principles outlined by William Vickrey.
In such a system, vehicles are charged based on when, where, and how much they drive.
Some transportation experts see TDP road pricing as a fairer, more effective means of charging road users and managing travel demand. 
The Trans-Mongolian Railway is the main rail link between Mongolia and its neighbors.
It begins at the Trans-Siberian Railway in Russia at the town of Ulan-Ude, crosses into Mongolia, runs through Ulaanbaatar, then passes into China at Erenhot where it joins the Chinese railway system.
A separate railroad link connects the eastern city of Choibalsan with the Trans-Siberian Railway.
However, that link is closed to passengers after the Mongolian town of Chuluunkhoroot.
Mongolia has a number of domestic airports with some of them having international status.
However, the main international airport is Chinggis Khaan International Airport, located approximately from downtown Ulaanbaatar.
Direct flight connections exist between Mongolia and South Korea, China, Thailand, Hong Kong, Japan, Russia, Germany, Kyrgyzstan, and Turkey.
MIAT Mongolian Airlines is Mongolia's national air carrier operating international flights, while other domestic air carriers such as Eznis Airways, AeroMongolia and Hunnu Airlines are serving both domestic and regional routes.
Many overland roads in Mongolia are only gravel roads or simple cross-country tracks.
There are paved roads from Ulaanbaatar to the Russian and Chinese border, from Ulaanbaatar east- and westward (the so-called Millenium Road), and from Darkhan to Bulgan.
A number of road construction projects are currently underway.
Mongolia has 4,800 km of paved roads, with 1,800 km of that total completed in 2013 alone.
Mongolia Cup is the top football knockout tournament in Mongolia. 
Post war.
Modernization efforts.
With the end of the war, Mongolia embarked on a policy of “construction of the foundations of socialism."
Proclaiming it “necessary to exterminate the concept of property,” Choibalsan looked to modernize the country based on the Soviet model while expanding the communal agriculture sector.
Funded largely through Soviet aid, the country’s first five year plan (1948-1952) focused on economic development, infrastructure construction, and doubling the country’s livestock – a goal it failed to achieve.
Initiatives also were taken to redevelop the agrarian, industrial, transportation.
Under his government the Nalaikh coal mine, the electric grid, Züün Bayan petroleum factory, other metal and mineral factories, the Naushk-Ulaanbaatar rail road and other transportation systems were developed.
and communications sectors, to establish modern mining, and improve education and health services.
In addition to establishing the country's first major university, Choibalsan initiated policies to increase literacy rate and developed the 10 year elementary, middle and high school system.
The 1949 Communist victory in China eliminated, at least temporarily, the threat on Mongolia's southern border allowing the MPR to begin reducing its 80,000-troop army.
Defense expenditures dropped from 33 percent of the total budget in 1948 to 15 percent in 1952.