I have received a question from one of my blog readers, asking why JR East operates not electric cars but diesel vehicles on the Senseki-Tohoku Line. That is a good question. Since both the Senseki and the Tohoku sections of the Senseki-Tohoku Line are electrified, it is natural to think that electric cars should be used for this route.
In answer to the question...
Firstly, the electric system is different in each section. The Senseki section has a 1,500 V direct current (DC) system, whereas the Tohoku section has a 20,000 V and 50 Hz alternate current (AC) system. It costs much to make DC-AC dual system trains for the Senseki-Tohoku Line. Secondly, construction of an un-electrified track is cheaper than that of an electrified track as the connecting line between the Senseki and Tohoku sections. As a result, the (hybrid) diesel vehicle is adopted as the Senseki-Tohoku Line train.
Now, the passengers traveling in the Sendai-Ishinomaki area can choose one of two routes, namely, via the Senseki-Tohoku Line or via the Senseki Line. The train via the Senseki-Tohoku Line is suitable for flying passengers, who travel between two major cities (Sendai and Ishinomaki) directly, as it is fast. On the other hand, the train via the Senseki Line is convenient for passengers who get on/off at way stations, as it is operated frequently.
The EMU 205-3100 series is operated on the Senseki Line. It is a 4-car train (2M2T) with snow-resistant brakes and cold-resistant door systems.
