Despite long queues at bus stations and overcrowded buses, no more services can be added on the two busiest bus routes in the Expo site for fear of traffic jams, the city's traffic authority said on Monday.

There are always long lines of passengers waiting to board on the Shibo Avenue and Cross-River bus routes.

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The shortest interval between buses on the two routes has been shortened to 13.6 seconds, Zhou Huai, deputy director with the Urban Transport Management Bureau, told a press conference on July 5.

The five bus routes in Pudong and another four in Puxi serve the equivalent of 635,000 people on average a day, more than double the average daily attendance. The Shibo Avenue and Cross-River routes are the busiest.

About 60 buses have been added to the routes since Expo test operations began on April 20, bringing the total number of buses to 201.

However, they still can't keep up with demand. Visitors still have to wait for more than 30 minutes to get on at some busy stops. Many buses drive by without stopping as they are already packed.

Zhou said there had been plans to remove seats on the buses to increase capacity, but this was a non-starter because some batteries were placed under the seats of the new-energy buses.

All the buses at the Expo use clean energies and the event is also serving as an experiment before the buses are put into use outside the site after the Expo ends.

There had been very few problems with any of the cutting-edge new-energy vehicles at the Expo since test operations began, Zhou said.

Thunderstorms and hot weather had no impact on the buses' operations, he added, although all the buses stopped for 13 minutes on Sunday during a sudden thunderstorm, but Zhou said was because of low visibility rather than problems with the vehicles.

Another reason for a bus not running would be if the air conditioning system needed repairs, Zhou said.

The public transport system in the 3.28 square kilometer core area of the site serves the equivalent of about a million visitors every day, accounting for more than 13 percent of the total capacity of the city's transport system.

Meanwhile, non-Expo taxis will be allowed to pick up visitors at all nine Expo entrances from 7pm from next week to meet the increasing demand for taxis in hot weather, Zhou said.

Only 4,000 Expo cabs are allowed into the 7-square-kilometer restricted area at present to pick up passengers during the day. Non-Expo taxis can pick up visitors after 9 pm.