The Transpennine Route Upgrade (TRU) is a major investment being made in the railway between York and Manchester via Leeds and Huddersfield in the north of England. It is the 76 miles (122 km) northern route over the Pennines, most of which is also known as the Huddersfield line. As of 2024^[update], the line is heavily used but is slow and lacks capacity. It has Victorian infrastructure, covers difficult terrain including the 3-mile (4.8 km) Standedge Tunnel, and has poor access roads.

Since the closure of the Woodhead line, there are three remaining transpennine rail lines that connect Lancashire and Yorkshire. To the south of the Huddersfield line is the Hope Valley Line which traverses even more difficult terrain including the 3.5-mile (5.6 km) Totley Tunnel, and which in 2021 was allocated £137 million investment to improve capacity and connectivity between Manchester and Sheffield. To the north the Calder Valley line connects Manchester and Leeds via Rochdale and Bradford (where trains have to reverse). This line has been strengthened to allow its use as a diversionary route while the Huddersfield line is upgraded.

Reopening the Woodhead line as a potential alternative Pennine crossing was ruled out early on. The Skipton–East Lancashire Rail Action Partnership is a campaign that is seeking the reopening of the 12-mile (19 km) railway line that used to run between the Lancashire town of Colne and the Yorkshire town of Skipton. This could provide an additional transpennine route for both a commuter service and a relief transpennine freight route.

Since the rejection of Northern Powerhouse Rail's aspiration for a new high speed line within Yorkshire, it has been questioned whether an upgraded Huddersfield line will provide sufficient capacity for the region's needs. However, the Integrated Rail Plan for the North and Midlands (IRP) that was announced in November 2021, did include full electrification between Manchester and York, and subsequently W12 loading gauge to accommodate 2.9 m × 2.6 m (9.5 ft × 8.5 ft) refrigerated shipping containers throughout. The whole £9–11.5 billion programme has been defined as phase one of Northern Powerhouse Rail, and is claimed to be the biggest infrastructure project in the UK. It consists of a succession of sub-projects designed to give incremental benefits to rail users over a period of time, with an anticipated overall completion date of between 2036 and 2041. Following completion of the upgrade trains will be able to run at top speeds of 125 mph (201 km/h). In Manchester, the project interfaces with the Northern Hub.

There were up to 50 million passenger journeys per year on this line pre COVID-19 on fast (including TransPennine Express), semi-fast and stopping trains, as well as freight trains. The existing passenger service is widely accepted as being very unsatisfactory in terms of journey time, frequency, punctuality and level of passenger comfort. At its worst, 15% of passengers had to stand in peak times. The 50-mile (80 km) railway line between Leeds and Manchester links two key population centres. Leeds is the largest city in Yorkshire, and forms the main area of the City of Leeds metropolitan borough. It is the central city of the Leeds City Region which has a population of over 3 million, making it the second most populated metropolitan city region in the United Kingdom, behind Greater London. Manchester is the most-populous city and metropolitan borough in North West England. It lies within the third most-populous county, at around 2.8 million people. Manchester is often referred to as the second city of the United Kingdom, although this is disputable. York was voted European Tourism City of the Year in June 2007. Linking these population centres together by a low-polluting, low-carbon mode of transport such as electric trains is now seen as both desirable and essential.

The equivalent transpennine road link is the M62 motorway, which provides the most practical route for heavy goods vehicles and other commercial traffic between Manchester and Leeds. However, the section between junctions 18 and 29 through Greater Manchester and West Yorkshire has been identified as one of the most congested roads in Britain. Three of the five largest metro areas in England that contain a significant number of warehouses requiring deliveries to and from the ports at Merseyside and the Humber, are linked by the M62. Annual average daily traffic flows of 100,000 were recorded east of the Pennines at junction 22 in 2006 and 78,000 west of the Pennines. The UK government has long recognised the advantages of modal shift from road to rail.

Most main railway lines in England radiate out from London with very few, such as the transpennine routes, going at right angles to these. It is widely accepted that there is a North–South divide in England, with government spending per person on drivers of growth such as transport infrastructure, being far higher in the South-East than the North. London has a directly elected mayor with control over public transport whilst most Northern cities have transport policies decided by Westminster. In 2021, the Conservative government launched a Levelling up policy to address the North–South divide as part of a broader objective. All of the above factors mean the Transpennine Route Upgrade is high on the political agenda for all parties.

In March 2021, Parliament's Transport Select Committee published a report in the series of Trains Fit for the Future enquiry. It recommended a rolling programme of electrification. There was also a call for the Department for Transport (DfT) to publish without delay a list of “no regret” electrification schemes, and then for the industry to act on them. The report also reached the mainstream media with headlines of “MPs call for a rolling programme of electrification”.