Historically, Italy had two unusual dominant track gauges which were legally defined depending on the terrain encountered. The gauge of was used for the national Italian rail network and was very similar to the standard gauge commonly used elsewhere in the world.
Since the 1930s, the gauge has been adopted as the standard and gradually replaced the track gauge. Thus, in Italy, only a few older tram systems, such as the Milanese tramway network, remain equipped with .
The other popular gauge, a narrow gauge, was defined at and is very similar to the metre gauge – – commonly used in many other parts of Europe and thus came to be known as "the Italian metre gauge".
Italian law has defined its track gauges in terms of the distance between the centres of each rail,[1] rather than the inside edges of the rails, giving some unusual measurements. According to the law of 28 July 1879, the only legal gauges in Italy were,, measured between the rail centres, which correspond to and between the rail inside edges.
The narrower gauge has 1,000 mm between the centres of the rails, which explains the name Italian metre gauge, but it is 950 mm in gauge when measured from the inside of the rails, as gauges are normally measured in other countries.
A disadvantage of measuring from the centre of the rail is that the width of the rail varies and affects the gauge. It is easier and more reliable to measure from the inner edges of the rails.
The following systems survive today:
Outside Italy, the Madrid Metro also uses this gauge.
See main article: Rail transport in Italy. The Italian standard gauge railway system has a total length[2] of 24227km (15,054miles) of which active lines are .[3] The network is recently growing with the construction of the new high-speed rail network.
See main article: Narrow-gauge railways in Italy. In Italy, track gauges of,,,, and are or were present.
The aforementioned "Italian metre gauge" was also used in the former Italian colonies of Eritrea (Eritrean Railway), Libya (Italian Libya Railways), and Somalia (Mogadishu-Villabruzzi Railway).