Keikyū Zushi Line

The line was opened on 1 April 1930 by the Shōnan Electric Railway as the section between Kanazawa-hakkei and Shōnan-Zushi, laid to standard gauge. On 1 April 1931 Jimmuji Station opened, the line was extended by 0.4 km, and a Hayama-guchi (Hayama-side) boarding point was added at Shōnan-Zushi while the original stop became the Numama-guchi boarding point. The young railway was soon swept up in the wartime consolidation of Japan's private lines: it was absorbed into the Keihin Electric Railway on 1 November 1941, and on 1 May 1942 Keihin in turn merged into Tokyu — the so-called "Greater Tokyu" — making the route part of the Tokyu Shōnan Line.

The war years brought retrenchment as well as expansion. On 1 September 1942 the Hayama-guchi boarding point was closed and the line was cut back to the Numama-guchi stop, which was renamed Shōnan-Zushi. In 1943 a temporary station, Mutsuura-shō, opened on 15 February for naval personnel between Kanazawa-hakkei and Jimmuji, and on 15 October the Kanazawa-hakkei–Shōnan-Zushi stretch was reduced to a single track. Jimmuji Station was moved to its present site on 1 September 1944.

After the war the line returned to Keikyū's hands and steadily recovered. Keihin Electric Express Railway was separated out of Tokyu on 1 June 1948, and that same year the Zushi end was rebuilt: the Zushi-Kaigan terminus revived the old Hayama-guchi on 3 July 1948, the Kanazawa-hakkei–Jimmuji section was re-doubled on 16 August, and through running between Yokohama and Zushi-Kaigan began on 6 September. The wartime temporary stop was replaced by the present Mutsuura Station, relocated and reopened on 1 March 1949, and from 10 July 1949 through trains ran between Shinagawa and Zushi-Kaigan, tying the seaside terminus directly into Keikyū's trunk route toward Tokyo.

The line's two Zushi-area termini were eventually consolidated. Shōnan-Zushi was renamed Keihin-Zushi on 1 November 1963, and on 2 March 1985 Keihin-Zushi and Zushi-Kaigan were merged into a single new station, Shin-Zushi, built at the midpoint between them; this shortened the line by 0.2 km to its present length of 5.9 km. In later decades the service pattern was reshaped around through running to central Tokyo and Haneda: a limited-express (tokkyū) service was introduced on 31 July 1999, the safety system was upgraded to C-ATS on 14 February 2009, and on 16 May 2010 an Airport Express began calling at every station on the line.

The Zushi Line has a distinctive operational feature: part of it is laid with dual-gauge (three-rail) track. Because the Sōgō Sharyō (J-TREC) Yokohama plant — the former Tokyu Car Corporation works — sits beside the Keikyū Main Line near Kanazawa-hakkei, newly built rolling stock is moved over the Zushi Line's three-rail section to and from Zushi Station on the JR Yokosuka Line. This lets standard-gauge Keikyū cars and 1,067 mm narrow-gauge vehicles bound for JR and for Keikyū's through-service partners be transferred between the factory and the national network.

Station numbering was introduced on 21 October 2010, and since that date the 2.8 km between Mutsuura and Jimmuji has been the longest interval between adjacent stations anywhere on the Keikyū network. The terminus, Shin-Zushi, was renamed Zushi·Hayama on 14 March 2020 to advertise access to the resort and former imperial-villa town of Hayama, and from 25 November 2023 the line's Airport Express services were redesignated simply as Express. Hayama itself has no railway station, so visitors reach it by Keihin Kyūkō bus from Zushi·Hayama, and Keikyū markets discount excursion tickets such as the "Hayama Joshi-tabi" pass for the trip; all trains stop at all four of the line's stations.

• 19301 April: the Shōnan Electric Railway opens the line between Kanazawa-hakkei and Shōnan-Zushi, built to 1,435 mm standard gauge.
• 19311 April: Jimmuji Station opens; the line is extended 0.4 km and a Hayama-guchi boarding point is added at Shōnan-Zushi, the original stop becoming the Numama-guchi boarding point.
• 19411 November: the line is absorbed into the Keihin Electric Railway.
• 19421 May: Keihin Electric Railway merges into Tokyu (the 'Greater Tokyu'), and the route becomes part of the Tokyu Shōnan Line; on 1 September the Hayama-guchi point is closed and the line is cut back to Numama-guchi, renamed Shōnan-Zushi.
• 194315 February: the temporary Mutsuura-shō Station opens for naval personnel between Kanazawa-hakkei and Jimmuji; 15 October: the Kanazawa-hakkei–Shōnan-Zushi section is single-tracked.
• 19441 September: Jimmuji Station is relocated to its present site.
• 19481 June: Keihin Electric Express Railway (Keikyū) is separated from Tokyu; the Zushi end is rebuilt — Zushi-Kaigan Station revives the Hayama-guchi (3 July), Kanazawa-hakkei–Jimmuji is re-doubled (16 August), and Yokohama–Zushi-Kaigan through service begins (6 September).
• 19491 March: the wartime temporary stop reopens, relocated, as the present Mutsuura Station; 10 July: through service begins between Shinagawa and Zushi-Kaigan.
• 19631 November: Shōnan-Zushi Station is renamed Keihin-Zushi.
• 19852 March: Keihin-Zushi and Zushi-Kaigan stations are merged into a new Shin-Zushi Station at the midpoint between them; the line is shortened by 0.2 km to its present 5.9 km.
• 199931 July: a limited-express (tokkyū) service is introduced on the line.
• 200914 February: the line's safety system is upgraded to C-ATS.
• 201016 May: an Airport Express begins running, calling at every station on the line; 21 October: station numbering is introduced.
• 202014 March: Shin-Zushi Station is renamed Zushi·Hayama.
• 202325 November: the line's Airport Express services are redesignated simply as Express.