Northern Line has four tunnels shown in the table below.
(a) Judging from the result of regular cross-section inspection, deformation or the like is not progressed and therefore, these tunnels are considered to be stable.
(b) These tunnels are constructed in accordance with the construction gauge of the standard railway gauge. Therefore, there is a large gap between the construction gauge and the car gauge and thus, there may be no problem even if car vibration increases.
(2) Bridge
(a) The outline of bridges on Northern Line are shown below by the values of three permanent-way maintenance depots for reference.
(b) The bridges were successively constructed in accordance with the construction of Northern Line. Therefore, though they were constructed between 1901 and 1926, most bridges were constructed before 1910.
