Police are seeking witnesses after the arson attack at 3am damaged signal cables on the line between Oerlikon and Zurich airport.
Train travel between the city and Kloten airport was disrupted for around 16 hours yesterday, though trains were finally running again at 7pm, said news agencies.
The damage caused by the fire, which forensics revealed was started deliberately, runs to several hundred thousand francs, police said in a statement.
The fire “resulted in numerous cancellations and had an impact on the entire rail traffic in the region,” police said.
“Thousands of train passengers reached their destination only very late and with a lot of patience.”
Forensic specialists are investigating the damaged tracks and Zurich police are calling for witnesses.
The incident has raised questions over security on the line and the ease with which the signal cables were damaged.
Speaking to 20 Minuten, Kurt Schreiber of Pro Bahn Schwiez said "Even a child could do it", though he speculated: "I expect it was a former employee who knew exactly where the weak point in the system is."
Under Swiss law the arsonist could get up to a year in prison, or between three and 20 years if it's proven that he or she put people's lives in danger.
SBB could also claim compensation for the damage caused.
Stark bleiben, Pendler! Die Bahnstrecke zwischen Oerlikon und Zürich Flughafen bleibt bis 20 Uhr gesperrt. https://t.co/ztpJ8Hd9Hp— TA Zürich (@tagi) June 7, 2016
The problems caused commuter chaos, with large queues gathering to use trams between the airport and the city, and reports of taxis over-charging for the journey.
Speaking to news agencies, a spokesperson for Zurich airport said the incident had no impact on flights themselves, though 130 passengers attempting to use public transport to get to the airport missed their flights.
The fire was started under a viaduct near Schärenmoosstrasse between Oerlikon and Kloten airport.
Anyone with information should call police on 044 411 7117.