'The move will make passage across the river more efficient, reduce transport costs and allow the bridges and tunnels to be more fully utilised.' State newspapers said the plan would improve the investment climate in Shanghai and give a helpful push to the next stage of development in Pudong, the sprawling but less populated district on the Huangpu's east bank.

However, city planners had not realised just how many people in Shanghai would go along for a free ride.

Traffic backed up for kilometres from the main tunnel linking the two halves of the city. The honking horns and angry motorists gave planners pause for reflection.

Only two weeks later, state media - with a bit less fanfare this time - announced an abrupt U-turn in the effort to make full use of the bridges and tunnels.

Smaller-engine cars were banned from the main tunnel while taxis - which are usually larger cars - were restricted if they wanted to cross during the busiest 12 hours of the day.

A taxi with an odd-numbered licence plate could use the Yanan Road tunnel on Mondays, Wednesdays and Fridays while those with even numbers had Tuesdays, Thursdays and Saturdays.

Sundays were fair game for all.

This has led to somewhat comical scenes of passengers jumping into cabs only to hop out once they discover their chariot of choice cannot go through the tunnel. Sometimes passengers bail out - like bungee jumpers with second thoughts - just as their taxi nears the tunnel - much to the consternation of passing cars.

However, there are no such restrictions on the bridges and some taxi drivers gamefully suggest taking an alternative route.

That could mean a little Shanghai-style sightseeing, occasionally proving to be as direct as going from Central to Tsim Sha Tsui via Macau.

If you insist on such misguided travel on a regular basis, you might want to join a 'Mileage Plus' programme entitling you to a free trip once in a while.

The new and improved traffic system demands a bit of alertness on the part of passengers. They must briefly put down their newspapers, halt casual conversations or pause from clinching a promising business deal - just to ensure the approaching cab has the correct licence number.

It is also not recommended for those who have less than perfect vision to bravely venture out alone. One near-sighted friend relates a tale of frantically waving to a succession of cabs. Once they pulled up it became apparent they all had the wrong number.

The hapless traveller had to turn them away one after the other - like a fisherman throwing back a catch too small to keep.

Taxi drivers are also less than thrilled with the latest traffic improvements.

'It's a nuisance. Passengers paid the toll before anyway,' lamented one cabbie.

But the nice thing about a one-party system is never having to say you are sorry. Asked to explain the current predicament in the mainland's most open city, officials at the central office for traffic police helpfully suggested asking someone else.

The same question was directed at the city planning committee which recommended it be put in writing. Their answer is still anxiously awaited.

So commuters can only go with the flow - or lack of it.

Of course, they could always wait for Sundays.