Post-independence

Numerous improvements were implemented on Federal Route 1 after the independence of Malaya in 1957 and the formation of Malaysia in 1963. Among the earliest improvements was the construction of the Merdeka Bridge at the Penang–Kedah state border. It was constructed to replace the old bridge that was destroyed in 1942 during the Second World War. The bridge assumed its name for being opened to motorists during the year of Malayan independence.^[5]

In 1966, the Tanjung Malim–Slim River Highway FT1 was opened to motorists, becoming the earliest toll road in Malaysia.^[11] The two-lane highway bypassed the former section between Slim River to Tanjung Malim, which would later be downgraded to Perak State Route A121 and Federal Route 193.^[4][12]

The improvements of the FT1 route were also being implemented within the Federal Territory of Kuala Lumpur as well, in order to improve the highway network within the city. A lack of proper highway planning was blamed for the severe congestion in the city. At that time, the FT1 route within Kuala Lumpur consisted of Jalan Cheras, Jalan Pudu, Jalan Tun Perak (formerly known as Java Street and then Mountbatten Road), Jalan Tuanku Abdul Rahman and Jalan Ipoh (both previously known as Batu Road).^[13] Under the recommendation from the 1979 Klang Valley Review Report, the FT1 route in Kuala Lumpur was rerouted to a new road system consisting Jalan Loke Yew, Jalan Maharajalela, Jalan Kinabalu and Jalan Kuching as a traffic dispersal means as well as providing the constant continuity of the FT1 route in Kuala Lumpur.^[14] One of the components of the new road system was the Jalan Kinabalu viaduct, which was opened on 15 March 1963.^[15]

The government in 1977 proposed to build an alternative road that would later be known as North–South Expressway, due to severe congestion along Federal Route 1,^{[16][better source needed]} but economic uncertainties caused delays and the project was only revived in the 1980s under Mahathir Mohamad.^[1]

The most controversial development of the FT1 highway in Kuala Lumpur was the toll collection at Jalan Kuching FT1. The nine-year concession of Jalan Kuching FT1 was awarded to Kamunting Corporation Berhad, signed on 15 April 1985. In the original concessionaire agreement, Kamunting Corporation Berhad was required to build an interchange at Kepong Roundabout and to upgrade the Jalan Kepong FT54, in return for the nine-year toll collection rights starting from 1987 until 1996. However, in 1987, the concessionaire agreement was amended, and Kamunting Corporation Berhad was required to add two more lanes from the existing four lanes along Jalan Kuching FT1, resulting in another 7-year extension of toll concession which was ended in 2003.^[17] The toll collection at Jalan Kuching FT1 had sparked fury among Kuala Lumpurian motorists, and numerous protests were held to urge the government to end the toll collection there.^[17][18] The toll collection at Jalan Kuching FT1 was finally abolished on 8 January 2003.^[19]

Where the Jitra–Bukit Kayu Hitam section was constructed as an upgrade of the existing Federal Route 1 section into a divided highway with partial access control and at-grade intersections.^[16] At that time, the construction of the Kuala Lumpur–Seremban Expressway E2 was still ongoing, and therefore the expressway would later form the pioneer route for the southern route. Unlike the other sections of the North–South Expressway, the Jitra–Bukit Kayu Hitam section did not comply with the expressway standards defined by the Arahan Teknik 8/86: A Guide on Geometric Design of Roads which was only published by the Malaysian Public Works Department (JKR) later in 1986, resulting the section to be grandfathered as a part of the North–South Expressway E1.^[16] After the North–South Expressway was completed in 1994, the expressway took the role of the Federal Route 1 as the main backbone route in Peninsular Malaysia.^[20]

Apart from the Jitra–Bukit Kayu Hitam section that was being upgraded to be a part of the North–South Expressway E1, there are some other sections of the FT1 highway that have been upgraded to toll roads and controlled-access expressways. For example, the Skudai Highway FT1 was completed in November 1985 as a tolled divided highway until 1 March 2004.^[21] Meanwhile, Jalan Cheras–Kajang FT1 was upgraded from the former two-lane road into an eight-lane controlled-access expressway known as the Cheras–Kajang Expressway E7/FT1. The expressway was opened to traffic on 15 January 1999.^[22]

Much of the road remains in use, although in September 2009, portions of the road north of Ipoh were temporarily closed to facilitate double tracking and electrification along the Ipoh–Padang Besar railway line. In December 2022, a 9.4 km segment of the Ipoh-Butterworth trunk road has been renamed to "Jalan Tun Dr. S. Samy Vellu " in a tribute to the former works minister. This renaming, as per the Federal gazette, encompasses the stretch commencing at the Kinta-Kuala Kangsar district border and culminating at the junction of Taman Makmur in Sungai Siput, Perak.^[23][24]