The route from Leeds out to Selby runs roughly parallel, and between 0.6 and 2 miles (1 and 3 km) south of the route of the Leeds and Selby Railway.
The route begins just east of Leeds city centre at a junction with the A61, although, before its February 2009 realignment along the new East Leeds Link Road, it began at a junction with the A64 in the Halton Moor area of the city (now signed as the B6159). The road passes through the Knowsthorpe and Cross Green areas, as Pontefract Lane; despite being of dual carriageway standard, is subject to a 40 mph speed limit, and incorporates peak-time HOV lanes. At the end of this dual carriageway section, the route meets the M1, and the road continues north along the motorway for one junction then resumes as the A63.
From junction 46 of the M1, the Thorpe Park roundabout, the route continues east, meeting the A642 at Garforth. There is a turning for Lidgett Lane (B6137) to the left, next to Garforth Academy, with the Shell garage on the right. It crosses the Leeds Country Way (a former railway), and there is the B6137 to the right for Kippax. On the Garforth/Micklefield parish boundary is a roundabout with the A656 Roman Ridge.
At the Boot and Shoe junction, with the former A1, there is the Esso Boot & Shoe Service Station, and the Best Western Milford Hotel. There is a grade-separated left turn for the B1222 (for Sherburn-in-Elmet). This dual-carriageway section of the former A1, follows the Leeds – North Yorkshire boundary (Ledsham and South Milford), and was built as part of the Brotherton-Micklefield scheme in November 1964 by Dowsett Engineering Construction. At the Selby Fork junction south of the Selby Fork Hotel, the A1246 continues southwards along the former A1, and the road enters the district of Selby, in North Yorkshire.
It crosses the A1(M) at junction 42 at South Milford. It meets the A162 at a roundabout, crosses a railway, and passes through Monk Fryston. It follows Causeway Dike and passes through Hambleton, where to the east it crosses the Selby Diversion of the East Coast Main Line, and the A1238 (former A63) at a roundabout. The route follows the six-mile £44 million Selby Bypass and £5 million Barlby Bypass, the latter of which is shared with the north-south A19, although the A19 still passes through Selby itself. On the bypass the road passes Selby Golf Club, meets the A19 at a roundabout at Brayton, crosses the Selby Canal, crosses the Doncaster-Selby railway, meets the A1041 at a roundabout, and crosses the River Ouse (Ouse Swing Bridge) and the Selby-Hull railway. The short section around Barlby follows what was the old East Coast Main Line railway before the Selby Diversion opened in the early 1980s. An alternative route eastwards from the Selby bypass, to the M62, is the A1041 via Camblesforth, then the A645 past Drax power station. The route out to Hull is shadowed by the Selby-Hull railway line.
It leaves at the Barlby Roundabout (completed May 2013; formerly a dangerous road junction) to the right, passing Osgodby then over the railway line and passes Hemingbrough. A planned bypass at Osgodby (2002) was cancelled due to increases in prices of land. It crosses the River Derwent and enters the East Riding of Yorkshire. It passes through Newsholme before passing straight through Howden next to Howden Minster. It passes through the town as Bridgegate and Hull Road, passing Howden School, where it meets the A614 at a roundabout at the BP Longs Corner Garage. Access to the M62 is via junction 37 to the west, along Boothferry Road (A614).
From Howden, the A63 is renamed to be the B1230, at the Howden end but is still signposted as the A63. The B1230 continues and carries the A63 traffic over the M62 motorway and onwards into Gilberdyke. When the B1230 was originally the A63, the main road through Gilberdyke was a dual carriageway for about three miles to the other side of Newport. Where the B1230 crosses the M62 motorway at Newport, the M62 finishes and the A63 starts. Before the last eastern section of the M62 to be built, the motorway terminated at a temporary junction at Balkholme onto the A63 (now B1230). Before the M62 opened, the single carriageway A63 was Hull's main route to the South of England, causing many bottlenecks.
The section from junction 38 of the M62 (its terminus) to the A1034 junction near South Cave was single carriageway before the M62 opened in May 1976. The section was constructed as the dualling of the Caves Bypass and opened when the last eastern section of the M62 opened, completing the dual carriageway link to the outskirts of Hull. From junction 38, the B1230 leads to North Cave (and in the direction of Beverley) along the former A63. The BP Triangle North Cave is alongside the junction.
There is the Beacon Service Area on the eastbound side, with the South Cave East Little Chef and Shell Beacon, situated just south of Everthorpe and Wolds prisons. The road skirts the southern edge of South Cave, and near Ellerker it crosses the former route (and Ermine Street from Brough, then known as Petuaria, to York) at the A1034 junction.
The 2.5 miles (4 km) Elloughton bypass was built in October 1971, from the A1034 to the Welton/Brough junction passing Brantingham to the west. It replaced the former road through Elloughton and Brough. This section skirts the southern edge of the Yorkshire Wolds.
The Welton/Brough – North Ferriby section opened in 1961. At the Elloughton-cum-Brough-Welton parish boundary, there is a grade-separated junction for Brough to the south and Welton to the north. The road passes on the south side of South Hunsley School (with a leisure centre) at Melton, part of the parish of Welton.
A new grade separated junction was constructed east of Melton near North Ferriby in 2006/7. The Shell Grand Dale filling station is on the westbound side, west of the Melton interchange. The Yorkshire Wolds Way crosses at this point.
The North Ferriby bypass and North Ferriby – Hessle sections opened in 1961. The former route is partly the B1231 (for Swanland). The road meets the A15 at a grade-separated junction. The former route, before the South Docks Road improvement, followed the current A1105 into Hull.
The road continues through the Humber Bridge Country Park, across the Hull-Selby railway, and under the Humber Bridge. The Humber bridge was designed to take some of Hull's traffic southwards, but the vast majority takes the A63 westwards, towards the M18. The road passes on the south side of Hessle, next to Hessle railway station, and follows the Hull to Selby railway line closely on the southern side as far as the outskirts of Hull near the western docks.
The section from Hessle into Kingston upon Hull is named Clive Sullivan Way, after the rugby league player Clive Sullivan, (originally titled the South Docks Road) . There is a junction with Priory Way, and at Gipsyville it meets the A1166 at a grade-separated roundabout near St Andrew's Quay. Near the Albert Dock, there is a fly-over where it rejoins the former Hessle Road next to the Smith & Nephew factory to the south.Castle Street
The A63 meets the A1079 (for central Hull) at a junction, beyond which the road is named Castle Street. The Castle Street section of the road (2011) had significant air pollution problems (NO2 levels), with over 55,000 vehicles per day, and had heavy congestion, having been at full capacity for around a decade; much of the traffic is heavy goods vehicles originating as a result of Ro-Ro activity at Hull Docks. The road section also was experiencing high accident levels, as well as forming a barrier to local north-south movement within the town centre. Improvement schemes for the road had been planned since the 1980s, but were subject to funding delays.
Consultation on the design of a solution began 2009. Split level junctions including underpassing or overpassing the A63 were considered for the bottleneck at the Mytongate roundabout, with additional congestion easing measures, and pedestrian bridges. Other options included an extended viaduct and tunnel options – the consultation showed a preference for an underground solution. In March 2010 the Highways Agency established a preferred scheme – the A63 would be lowered 23-foot (7 m) at the Mytongate bottleneck, and the north south connecting roads raised slightly (3.3-foot (1 m)), creating a split level junction; additionally the eastbound carriageway would be widened, and pedestrian crossings created. If funded construction was planned to begin in 2016 for completion in 2019. The cost has been estimated at between £150 and £200 million. In May 2012 the design and consultation work was initiated. In June 2013 the government announced the go ahead for a £160 million improvement to the road after 2015.Garrison Road
It crosses the River Hull at Myton Bridge (a swing-bridge), near the Hull Tidal Surge Barrier and The Deep. The stretch over Myton Bridge and within the ward of Drypool is known as Garrison Road. Within Drypool there is a northwards junction with the A1165 (Great Union Street), and southwards junction connecting the Victoria Dock Village housing estate at the same point. The road terminates at a junction for the A1033 (Hedon Road).