Hong Kong has so many road tunnels that the thought of another coming into service would not usually cause much interest beyond those who use it. But the one that begins partial operation on January 20 by linking Central and North Point with a bypass beneath the harbour-side shores of the busy districts of Wan Chai and Causeway Bay, is reason for wider attention. Aiming to reduce congestion, travel times during peak hours are expected to be cut by dozens of minutes. The ramifications go much further, though; the diversion of traffic provides the chance to transform crowded and polluted streets to better reflect the needs of an international city.

Limited area means narrow streets, leading to congestion in busier districts. But the government has been reluctant to impose measures in wide use elsewhere such as road pricing and vehicle limits or bans. That has meant heavy roadside pollution in Central and Causeway Bay and a rejection of most efforts for pedestrian zones. The 3.7km tunnel was viewed as a vital part of the solution and authorities pledged to consider further measures after it opened.

With the eastbound section opening on January 20 and the westbound expected a month or so later, plans can now be considered. A crucial element will be easing bottlenecks on the approaches to the Cross-Harbour and Eastern tunnels, and enacting the pledge of Chief Executive Carrie Lam Cheng Yuet-ngor in October to double tolls at both and reduce them at the Western tunnel should help. Fewer vehicles will presumably improve roadside air quality, but that is only part of an approach to making streets on the north side of Hong Kong Island friendlier to shoppers and workers.