This site is an online media that delivers all sorts of trivia about the six Tohoku prefectures, from sightseeing and gourmet spots to local customs, history, and more
This time,the Ou Main Line and Senzan Lineexpress trains that ran onspecifically those that were operated by diesel railcars (DMUs) even though the entire section from the starting station to the final station was electrifiedwe will introduce Note that there were numerous cases where DMUs were used for special trains, making it difficult to investigate them all, so we will mainly focus on regular scheduled trains.
Furthermore, cases where only a portion of a train set runs under overhead wires for its entire route, even if the train has multiple starting and ending stations, are excluded. (In this case, the express train "Senshu" is excluded. "Senshu" trains had a section connecting Yonezawa Station and Aomori Station in addition to the sectionSendai Station and Aomori Station, the former runs on the non-electrified Rikuu East Line.)
The terms "diesel railcar" and "electrification"article on the Tohoku Main Linewere explained in
The Ou Main Line is a railway line that runsStationfrom FukushimaAomoriYonezawa, Yamagata, and Shinjo in Yamagata Prefecture, Yokote,Omagaripassing through stations such asAomori Prefecture. Since there are some differences in the roles that the line has played between Fukushima Station and Akita Station and between Akita Station and Aomori Station, this articletrains that traveled through the former section between Fukushima Station and Akita Stationwill focus on (trains that traveled through the latter section but did not enter the former section will be covered in future articles).
Until the opening of the Tohoku Shinkansen in 1982, the Ou Main Linea vital role in connecting the Tokyo metropolitan area and Fukushima Prefecture with the three prefectures of Yamagata, Akita, and Aomoriplayed With the opening of the Tohoku Shinkansen, and subsequently the Yamagata and Akita Shinkansen, its role as one of the main routes connecting the Tokyo metropolitan area and the Tohoku region declined. However, some sections are still part of the routes for the Yamagata Shinkansen's "Tsubasa" and the Akita Shinkansen's "Komachi," so it remains important. It should be noted that the names Yamagata Shinkansen and Akita Shinkansen are not the official line names, and the sections through which these trains pass (between Fukushima Station and Shinjo Station, and between Omagari Station and Akita Station) are officially still called the Ou Main Line.
The Ou Main Line was first electrified with DC power between Fukushima Station and Yonezawa Station in April 1949. Next, in November 1960, the section between Yamagata Station and Uzen-Chitose Station was electrified with DC power. In September 1968, the already DC electrified section was changed to AC electrification, and the section between Yonezawa Station and Yamagata Station was further electrified with AC power. In August 1971, the section between Akita Station and Aomori Station was electrified with AC power. Finally,October 1975,the section between Uzen-Chitose Station and Akita Station was electrified with AC power,the electrification of the entire linecompleting
We will not go into detailed explanations about DC and AC, but since the types of power sources used to run trains are different in DC and AC electrified sections, trains that are only compatible with one electrification method cannot run directly between both electrified sections
Following damage caused by heavy rains in July 2024, train service on the Ou Main Line resumed in April 2025 with the electrification equipment removed from the section between Shinjo Station and Innai Station in Akita Prefecture. Therefore, the Ou Main Line is no longer fully electrified. The reason for deciding to remove the electrification equipment is, as mentioned earlier, that the Ou Main Line is no longer the main route connecting the Tokyo metropolitan area and the Tohoku region.
Yamagata Station, one of the main stops on the Ou Main Line
Express "Zaou" (Ueno Station - Yamagata Station)
In June 1960, an express train was launched connecting Ueno Station in Tokyo and Yamagata Station in Yamagata Prefecture via the Tohoku Main Line and Ou Main Line (with stops at stations such as Omiya Station in Saitama Prefecture, Utsunomiya Station in Tochigi Prefecture, and Fukushima Station in Fukushima Prefecture)The. The train was given the nickname "Zao." name is thought to be derived from the Zao mountain range, which straddles the border between Miyagi and Yamagata Prefectures.
When it first appeared, the "Zao" was a traditional-style train with a locomotive pulling the passenger cars. Furthermore, between Ueno Station and Fukushima Station,Matsushimait operated coupled with
The "Matsushima" train operated between Ueno Station and Sendai Station. This was similar to how the Tohoku Shinkansen "Yamabiko" (mainly between Tokyo Station and Sendai Station) and the Yamagata Shinkansen "Tsubasa" (between Tokyo Station and Yamagata/Shinjo Station) later operated in conjunction between Tokyo Station and Fukushima Station.
In October 1963, the name was changed from "Zao" to "Zaō". Also, the number of daily round trips was increased from one to two.
A diesel railcar-based "Zaō" also appeared, and according to the September 1964 timetable, there were two round trips per day by diesel railcars (regular trains that ran daily) and one round trip by passenger cars (seasonal trains that ran only during certain seasons). The travel time between Ueno Station and Yamagata Station was about 6 hours and 10 to 30 minutes by diesel railcar train and about 7 hours and 30 minutes by passenger car train. Between Ueno Station and Kōriyama Station in Fukushima Prefecture,Iide" and "Bandaiit operated coupled with express trains such as
In the timetable for the following month, October 1964, there was one round trip per day for diesel railcars and one round trip for passenger cars. The number of diesel railcar trains was reduced, but in its place, the diesel railcar limited express "Yamabato"was created, connecting Ueno Station and Yamagata Station.
In 1968, with the completion of electrification from Fukushima Station to Yamagata Station, some "Zaō"to be operated by 455 series electric trainswere changed The travel time between Ueno Station and Yamagata Station for the electric "Zaō" trains was shortened to about 5 hours.
455 series train
The system consists of two round trips by electric trains and one round trip by diesel railcars. The diesel railcar trainruns under overhead wires for its entire route,, making it a diesel railcar express train.
The diesel railcar "Zaō" remained init was coupled with the diesel railcar express "Iide"because While there are a few instances of diesel railcars and electric trains being coupled and operated together, it is not generally done. Even if the entire operating section is electrified, if a train is operated in conjunction with a diesel railcar train, it must be operated by a diesel railcar.
Express Zao No. 1 Ueno 9:06 - Yamagata 15:05, bound for Koriyama. It was a seasonal train, so when it was cancelled, the Dewa, which was used in conjunction with it, also had fewer cars. pic.twitter.com/mzMT2bHmDA
The "Iide" was a train that ran between Ueno Station and Niigata Station, via the Tohoku Main Line, Ban'etsu West Line, and Shin'etsu Main Line. Because the section of the Ban'etsu West Line from Kitakata Station in Fukushima Prefecture to Niitsu Station in Niigata Prefecture was not electrified, it was impossible to make the "Iide" an electric train (as of 2025, the electrified section of the Ban'etsu West Line has been shortened to run from Koriyama Station to Aizu-Wakamatsu Station).
With the timetable revision in March 1972regular "Zaō" trains were discontinued, and all trains became seasonal or extra trains that only ran during peak seasons. The main reason for the reduction in "Zaō" service was that it was upgraded to the limited express "Yamabato," which ran on the same route.
After that, there was no major activity for a while, but with the opening of the Tohoku Shinkansen in June 1982, a regular "Zaō" train service was introduced with one round trip per day in the timetable revision implemented on November 15th. It is noteworthy that during this period, the "Zaō" train was coupled with the "Matsushima" train, which it had previously coupled with, between Ueno Station and Fukushima Station. In addition, one round trip of the seasonal "Zaō" train was also introduced, operating between Fukushima Station and Yamagata Station.
with the November 1982 timetable revisionthe diesel railcar "Zaō"was discontinued The "Iide" train, which was coupled with the diesel railcar "Zaō," was also abolished.
In March 1985, the regular "Zaō" service disappeared again, and only temporary trains continued to operate. The service ran between Ueno Station and Yamagata Station, or between Ueno Station and Shinjō Station. Also, at least all of the temporary "Zaō" trains listed in the timetable for that month were passenger trains.
The "Zaō" express train, which operated as a temporary service, was discontinued in August 1991 to allow the Yamagata Shinkansen "Tsubasa" to run on the Ōu Main Line. However, in November, the name "Zaō" was revived as the name of a rapid train running between Fukushima Station and Yamagata Station. The rapid "Zaō" reportedly operated until around 1999. Currently, there are no rapid trains operating between Fukushima Station and Yamagata Station.
Express "Oga" (operated by diesel railcar between Ueno Station and Akita Station)
In October 1961, a night train connecting Ueno Station in Tokyo and Akita Station in Akita Prefecture via the Tohoku Main Line and Ou Main Line (passing through stations such as Omiya, Utsunomiya, Fukushima, and Yamagata)Ogawas upgraded to The name likely originates from the Oga Peninsula in Akita Prefecture. Two years later, in October 1963,Ogait was renamed
Until 1968, the "Oga" was an overnight train pulled by a locomotive, but a major change occurred in October 1968. A using diesel railcars, the "Oga," , was introduced, running one round trip per day. For the first few years after its introduction, the DMU trainHakkodaran between Ueno Station and Fukushima Station, sometimes coupled with
The daytime diesel train "Oga" took over 10 hours to travel from Ueno Station to Akita Station. In a world where there are also overnight trains and the limited express "Tsubasa" that run the same route, I wonder if there were really people who used the daytime "Oga" for the entire journey.
, which was the route for the "Oga"completed in October 1975, so it should have been possible to switch from diesel railcars to electric trains after that. However, since diesel railcars continued to operate even after the electrification was completed, it became a diesel railcar express train that ran the entire route under overhead wires.
The Kiha 58 series Express Oga No. 1 daytime train was a regular diesel railcar service, while the Express Oga No. 1 was a nighttime or seasonal passenger train. While the passing 115 series trains are air-conditioned, the Express Oga No. 1 trains are all non-air-conditioned. pic.twitter.com/w8L7Mp1KRV
The reason the "Oga" train wasn't replaced by an electric trainthe electrification system changes along its routeis likely because The Tohoku Main Line, on which the "Oga" runs, had a dividing line at Kuroiso Station in Tochigi Prefecture: south of the station, the electric trains used 1,500V DC power, while north of it, they used 20,000V AC power (the current boundary is no longer within the Kuroiso Station premises but north of Kuroiso Station). To run across both electrification systems, an electric train compatible with both would be necessary. On the other hand, a diesel railcar could run directly regardless of the electrification system.
That being said, the "Zaō" train, which I mentioned earlier, also runs on the Tōhoku Main Line, but it has been replaced with the 455 series electric multiple unit (DC) train, which is capable of operating on both AC and DC power (excluding trains that are coupled with the "Iide" train). So why did the "Oga" train, which is not coupled with any other diesel multiple unit trains, remain a diesel multiple unit? It is probably because DC and DC electric multiple units were expensive, and there was likely a shortage of such vehicles. I think there were circumstances such as being able to electrify the "Zaō" train but not being able to procure the electric multiple units needed for the "Oga" train.
In 1982, with the opening of the Tohoku Shinkansen and Joetsu Shinkansen lines, a large-scale reorganization of limited express and express trains running on conventional lines in the Tohoku region took place. With the timetable revision on November 15, 1982, the daytime diesel express train "Oga"was discontinued. It had been in service for a short period of 14 years since its establishment in 1968, and until its discontinuation, there had been no change in its operation to diesel trains.
The "Oga" service was reduced to just one round trip of a seasonal overnight train using passenger cars. The remaining passenger train "Oga" was changed to an extra train that only ran during peak seasons in 1985, and after the beginning of 1995, it ceased operation altogether.
For more information on "Oga", please see the article below
Express "Komakusa" (Yamagata Station - Akita Station, Aomori Station)
The express train "Komakusa" debuted with the October 1970 timetable revision. It operated between Yamagata Station and Akita Station, with a journey time of approximately 4 hours. From its inception, it was operated using diesel railcars.
Incidentally, Komakusaan alpine plant that grows wild in the Zao mountain range and other areas.
In October 1975,the electrification of the section on which the "Komakusa" operatedwas completed, but it continued to be operated by diesel railcars, making it a diesel railcar express train that operated under overhead wires for the entire route.
In October 1978, the operating section was changed to Yamagata Station to Aomori Station. Since the electrification of the Ou Main Line from Akita Station to Aomori Station had been completed in August 1971, the "Komakusa" continued to be a diesel railcar express train operating under overhead wires for the entire section. Incidentally, the journey time for the southbound train from Yamagata to Aomori was 6 hours and 42 minutes, but the journey time for the northbound train was 7 hours and 41 minutes,a difference of 59 minutes for some reason.
At Aomori Station,Seikan Ferrythe train schedule allowed for transfers to For more information about the Seikan Ferry, please see the article below.
reason the "Komakusa" remained a diesel trainthe train it was coupled with was also a diesel trainis likely because The southbound train from Yamagata to AomoriGassan No. 1was coupled with Gassan No. 1 traveled from Shinjo Station via the Rikuu West Line, then south on the Uetsu Main Line from Amarume Station to Nezugaseki Station on the Sea of Japan side of Yamagata Prefecture. Since the Rikuu West Line is not electrified, it was not possible to make the "Gassan" an electric train.
Incidentally, the "Gassan No. 1" trainUetsu No. 2was coupled with This "Uetsu" was also a diesel railcar express train that ran entirely under overhead wires, so I plan to write an article about it later.
between Akita Station and Omagari StationTazawa No. 4was coupled with Furthermore, from Shinjo Station to Yamagata Station, it was coupled with the "Gassan No. 6" train from Nezugaseki to Yamagata.
"Tazawa No. 4" was a train that departed from Akita Station, traveled via the Tazawako Line from Omagari Station, and then headed south on the Tohoku Main Line from Morioka Station to Sendai Station. At the time, the Tazawako Line was not electrified, so electrifying "Tazawa" was impossible. Incidentally, the Tazawako Line was electrified in 1982 and is now part of the route of the Akita Shinkansen "Komachi," so it can be seen as a precursor to the "Komachi."
With the timetable revision on November 15, 1982and absorbed into the "Tsubasa" limited express on the Ou Main Linewas discontinued It seems that it was operated by diesel railcars with only one round trip per day until the very end. For more information about the "Tsubasa" limited express before the opening of the Yamagata Shinkansen, please see the article below.
Approximately 10 years after the discontinuation of the express train "Komakusa," in July 1992, the Yamagata Shinkansen's "Tsubasa" began operating between Tokyo Station and Yamagata Station. From Yamagata Station, where the "Tsubasa" departs and arriveslimited express train, "Komakusa,"began operating to Shinjo Station or Akita Station. However, prior to the extension of the Yamagata Shinkansen to Shinjo Station in December 1999, the limited express "Komakusa" was rerouted to operate only north of Shinjo Station and changed to a rapid train in March 1999. In December 2002, the rapid "Komakusa" also disappeared.
Currently, the only express trains operating between Shinjo Station and Akita Station are two down trains from Shinjo to Yokobori, one up train from Yokobori to Shinjo, and one down train from Yuzawa to Akita
Senzan Line
Senzan Line Route Map Lincun – Map: Own work by the uploader. Data used: Ministry of Land, Infrastructure, Transport and Tourism National Land Numerical Information (Administrative Area (N03), Railway (N02), Lake (W09)), CC BY-SA 3.0 https://commons.wikimedia.org/w/index.php?curid=97569553,
The Senzan Line isSendai Stationin Yamagata City, Yamagata PrefectureUzen-Chitose Stationa railway line connecting However, there are no trains that start or end at Uzen-Chitose Station; trains continue onto the Ou Main Line and run directly to Yamagata Station. In effect,a line connecting Sendai Station and Yamagata Station.
The current Senzan Line primarily serves commuter and school transport within the Sendai metropolitan area. While it also connects Sendai and Yamagata, express buses appear to be more dominant in this regard. However, in the past, it also played a role in connecting Sendai and Niigata, via lines such as the Senzan Line, Ou Main Line, and Yonesaka Line (passing through stations in Yamagata, Yonezawa, and Sakamachi in Niigata Prefecture).
The electrification of the Senzan Line began in November 1937 with the use of direct current (DC) between Sakunami Station and Yamadera Station. Meanwhile, in August 1955, the section between Rikuzen-Ochiai Station and Kumagane Stationelectrified with alternating current (AC), making the Senzan Line a mixed line of DC and AC electrified sections.
In September 1957, the sections between Sendai Station and Rikuzen-Ochiai Station, and between Kumagane Station and Sakunami Station, were electrified with alternating current. The area within Sakunami Station became the boundary between DC and AC electrification.
In November 1960, the section between Yamadera Station and Uzen-Chitose Station was electrified with DC power. At the same time, the section of the Ou Main Line between Yamagata Station and Uzen-Chitose Station was also electrified with DC power, so the section from Sendai Station to Yamagata Station became electrified.
In addition, in November 1968, the DC electrified sections were changed to AC electrification, and the entire Senzan Line became an AC electrified line, which remains the case to this day
Although the Senzan Line was initially electrified with direct current (DC), it was later converted to alternating current (AC) electrificationbecause it was chosen as an experimental site for the practical application of AC electrification. The data and technology obtained from the Senzan Line tests led to the subsequent electrification of main lines, mainly in the Tohoku, Hokuriku, and Kyushu regions, using AC. In addition, sections of the Senzan Line and the Ou Main Line that were already electrified with DC were also converted to AC electrification, similar to the electrification methods of surrounding lines.
Furthermore, all Shinkansen lines, including the Tokaido Shinkansen which opened in 1964, are electrified with alternating current without exception. The results of the tests conducted on the Senzan Line also contributed to the birth of the Shinkansen.
The express train "Senzan" (which operated under overhead wires using diesel railcars between Sendai Station and YamagataStation)
The "Senzan" train service began operation in October 1963 with the revised timetable, connecting Sendai Station to Yamagata Station and Kaminoyama Station (now Kaminoyama Onsen Station) via the Senzan Line and Ou Main Line. It initiallya semi-express trainwas
The sections of the Senzan Line and the Ou Main Line between Yamagata Station and Uzen-Chitose Station were already electrified. Therefore, the "Senzan" service, which ran two round trips a day between Sendai Station and Yamagata Station,a diesel railcar semi-express service operating under overhead wires for its entire route from the beginningwas Similarly, for the train that ran one round trip a day between Sendai Station and Kaminoyama Station, the non-electrified section was only a mere 12.1 km from Yamagata Station to Kaminoyama Station.
In October 1968, the "Senzan" trainwas upgraded to an express train. All three round trips per day then ran between Sendai Station and Yamagata Station.
Furthermore, both the northbound and southbound trains, specifically trains 1 and 2, were replaced with electric trains. Train 3, however, continues to operate using diesel railcars, even though the entire section is electrified. I speculate that the reason it remained a diesel railcar is either because there wasn't enough electric train, or because the diesel railcars used for train 3 were being repurposed for other diesel railcar trains. The travel time between Sendai Station and Yamagata Station differed considerably: about 1 hour and 10 minutes by electric train and about 1 hour and 40 minutes by diesel railcar.
Ten years after its upgrade to an express service, in October 1978,the last remaining round trip operated by diesel railcars was also converted to electric trains, thus ending the 15-year history of diesel railcar express trains operating entirely under overhead wires, which had continued since 1963.
The 455 series on the Senzan Line still retains its green green car stripe! Even though it was only for operational reasons, the combination of the Showa-era express train "Senzan-Risshakuji" and this temporary train, which had a green car for only about an hour of service, is quite impactful. It even has a defroster! The Kiha 55s lined up at Yamagata Station are also lovely. pic.twitter.com/UDP3gbNVa0
With the timetable revision on November 15, 1982, the Senzan was downgraded to a rapid train, ending its history as an express train
In March 1985, all regular trains running on the Senzan Line, including local trains, were converted to electric trains, and there is no longer any trace of the old diesel railcars and passenger trains that once ran on the line
The "Senzan" rapid train service continued for some time, but its name was discontinued in 2004. However, rapid trains on the Senzan Line still operate as of 2025.
![1620px-JR_East_Innai_Station_Platform,_Akita_Pref](https://jp.neft.asia/wp-content/uploads/2024/12/1620px-JR_East_Innai_Station_Platform_Akita_Pref-150x150.jpg.webp "Trains will no longer be able to run!? What does "de-electrification" mean for the Ou Main Line? [Akita/Yamagata]")
