The Chicago Transit Authority (CTA) in the US is set to start a $30m track improvement project to modernise the Purple Line Express and eliminate slow zones.
As part of the project, improvements will be carried out on tracks between the Jarvis and Lawrence stations.
The project will upgrade track infrastructure and provide a faster, smoother and more reliable service to customers.
Chicago mayor Rahm Emanuel said: "Modernising our rail lines has been a critical piece of the comprehensive investment we’re making in Chicago’s world-class transit system.
"This major investment in the Purple Line Express complements improvements we are making to rail service throughout the city, and will provide better service to customers who live in Chicago or are commuting into the city to work, go to school or visit this great city."
CTA has also recently made several improvements to the Purple Line service, which includes the ongoing Ravenswood Connector project that is rehabilitating tracks shared by Brown and Purple Line Express trains between Armitage and the Merchandise Mart.
The work also follows a major track improvement project completed in 2013 that rehabilitated tracks and removed slow zones between Howard and Linden.
CTA president Dorval Carter Jr said: "The CTA is committed to modernising our rail system for the more than 13,000 daily riders on the Purple Line Express.
"Once work is completed, the Purple Line Express will provide customers with a more reliable and comfortable commute."
Work under the four-month $30m project is scheduled to start this month with construction expected to be completed by the end of November next year.
The scope of work will include replacement of track ties, restoration of track alignment and partial replacement of running rail along aging Purple Line Express tracks that serve more than 3.5 million passenger trips each year.
The CTA noted that construction on the tracks will take place on solely on week nights and weekends to minimise impacts to neighbouring homes and businesses.