Southern District

The route begins at the eastern end of Aberdeen Praya Road [zh] outside Ocean Court. Beyond the starting point, the road continues along the Hong Kong Island coast towards Tin Wan and Pokfulam. Immediately after the starting point, the route intersects with Ap Lei Chau Bridge at a trumpet interchange, providing the sole road connection to the eponymous island.

Route 1 continues along Wong Chuk Hang Road, with a short viaduct over the intersection with Nam Long Shan Road [zh]. At the end of the viaduct, there is another trumpet interchange connecting Ocean Park. The route then enters a T-interchange, where Wong Chuk Hang Road diverges from Route 1 and continues towards Repulse Bay and Stanley. Route 1 instead heads northeast towards Aberdeen Tunnel, the only highway tunnel connecting northern and southern Hong Kong Island. After passing through the toll plaza, the route enters the southern tunnel portal.

• Interchange with Ap Lei Chau Bridge
• Wong Chuk Hang Road and viaduct at night
• Aberdeen Tunnel southern portal

Wan Chai District

Upon leaving the tunnel, traffic runs on the Wong Nai Chung Gap Flyover [zh]^{[lower-alpha 1]} after exiting the tunnel at Happy Valley, running above Wong Nai Chung Road. At this point, a diamond interchange connects Wan Chai and Causeway Bay with Route 1 via Queen's Road East and Leighton Road.

Route 1 then continues into the Canal Road Flyover, with another pair of on/off-ramps outside Times Square accessible from the north. It then descends to the ground level into Wan Chai Interchange, a complete interchange intersecting with Gloucester Road (part of Route 4 before 2019), allowing traffic to head west into Admiralty and Central; or eastwards to Tin Hau and further onto the Island Eastern Corridor.

The route then heads into the Cross-Harbour Tunnel, the first underwater road crossing across the Victoria Harbour. The Central-Wan Chai Bypass (current route of Route 4) passes directly beneath the southern portal, but is not connected to Route 1.

• Wong Nai Chung Gap Flyover (top) and Wong Nai Chung Road (bottom)
• Canal Road Flyover
• Wan Chai Interchange before the opening of the tunnel
• Inside the Cross-Harbour Tunnel

Kowloon

Upon reaching Kowloon, Route 1 passes through the toll plaza and bus interchange of the Cross-Harbour Tunnel, situated between Hung Hom station and the Polytechnic University. It then merges into Hong Chong Road [zh], a short trunk road that ends at the junction with Chatham Road North (Route 5), where traffic to/from the Cross-Harbour Tunnel is connected with both directions of Route 5 via ramps laid out in a trumpet interchange fashion. Immediately after this junction, Route 1 is joined by traffic from Chatham Road South and Hung Hom Bypass [zh].

At this point, route 1 continues to head north on Princess Margaret Road, between the neighborhoods of King's Park and Ho Man Tin. It intersects with Fat Kwong Street at a partial cloverleaf interchange. Continuing northwards, it travels over Argyle Street via an overpass, before merging into Waterloo Road which originates from Yau Ma Tei. It then reaches another overpass across Prince Edward Road West and Boundary Street, which are single-directional arterial roads stretching across Kowloon in the westbound and eastbound directions respectively. At here, traffic from Sham Shui Po can switch to both directions of Route 1; southbound traffic on Route 1 can also exit and head towards Mong Kok or Kowloon City.

Route 1 then continues northwards, cutting through the middle of Kowloon Tong. The stretch between Flint Road and Suffolk Road is the only section of the route that is not a controlled-access highway, with numerous signal-controlled intersections. After Suffolk Road, Route 1 enters a 650m-long overhead viaduct, allowing grade separation from the ground-level intersections with Junction Road and Cornwall Street [zh].

After leaving Kowloon Tong, Route 1 climbs a steep, curvy incline to reach a partial clover interchange with Lung Cheung Road (Route 7), where ramps allow traffic from both directions of Route 7 to merge into Route 1 towards the north. Route 1 then heads into the 1.4km-long Lion Rock Tunnel, travelling under Lion Rock and heading into the New Territories.

• Cross-Harbour Tunnel
• Traffic congestion at Hong Chong Road
• Princess Margaret Road near Hong Kong Metropolitan University
• Waterloo Road at Kowloon Tong
• Southern portals of Lion Rock Tunnel

Sha Tin

After passing through the toll plaza at the northern end of the tunnel, Route 1 continues into Lion Rock Tunnel Road, continuing in a northeastern direction roughly along the eastern edge of the Sha Tin New Town. It then intersects with Hung Mui Kuk Road at a trumpet interchange, which continues into Tai Wai. After passing Sun Tin Wai Estate, Route 1 then runs along Sha Tin Road, diverging from Lion Rock Tunnel Road which heads into Sha Tin town centre instead.

The remaining 3 km section along Sha Tin Road is the only expressway section of Route 1. At Sha Tin Wai, the Sha Lek Highway splits off, heading towards an interchange with Route 2 towards Ma On Shan or Kowloon East. This is immediately followed by a diamond interchange with Sha Tin Wai Road. The route then turns northwards, passing by City One with a partial diamond interchange leading onto Tai Chung Kiu Road [zh]. It then crosses over the Shing Mun River via the 500m-long Dragon Bridge.

Across the river, Route 1 reaches another partial diamond interchange with Yuen Wo Road [zh], accessible from the northern side. It then joins Tai Po Road - Sha Tin at Fo Tan, where the traffic continues northwards via Route 9 towards Tai Po and Fanling. On the northbound direction, Route 1 continues along Tai Po Road for another 250m as the outermost vehicular lane, reaching another exit ramp towards Penfold Park before merging into Route 9.

• Lion Rock Tunnel toll plaza
• Sha Tin Road passing under Tuen Ma line tracks
• Dragon Bridge

Expansion of Lion Rock Tunnel

The Highways Department has proposed to enlarge the existing Lion Rock Tunnel and widen its connecting roads,^[2] in order to refurbish the tunnels which has shown signs of aging and deterioration, as well as to help alleviate congestion around the tunnel and adjacent sections of Route 1.^[3]

Upon completion, the existing southbound tube will be refurbished and widened to three lanes, and a new three-lane tube will be constructed between the existing tubes, taking over the northbound traffic. The existing northbound tube (Second Lion Rock Tunnel) will be taken out of regular use, and serves as a backup carriageway during emergencies.^[4] In addition, the section of the Lion Rock Tunnel Road from the Sha Tin portals to Fung Shing Court will be widened from two to three lanes in both directions. To the south of the tunnel, the two slip roads connecting Lung Cheung Road to / from the east (Wong Tai Sin direction) will be widened from one to two lanes.^[3]

The project is currently expected to start construction by 2025 and projected to be fully open by 2033.^[5]

Trunk Road T4

The proposed Trunk Road T4 [zh], which is currently under design works,^[6] will be connected to the Route 1. Diverging from Sha Tin Road to the west outside Pok Hong Estate, the new route would cross the Shing Mun River and merge into Tsing Sha Highway (Route 8) and Shing Mun Tunnels (Route 9). In addition, an entrance slip road from Lion Rock Tunnel Road outside Tsang Tai Uk towards northbound Sha Tin Road will be built.^[6] Construction is expected to start in late 2023.^[7]