An overhaul of rail services will lead to the end of "cattle truck" overcrowding on the county's cramped mainline rush-hour trains.
Under the shake-up, announced by ministers yesterday, the under-threat Gatwick Express will be saved while 12,000 extra seats will be provided every day for commuters travelling from Sussex stations to London.
The announcement comes after a three-year review into how one of the country's busiest commuter routes could be improved.
Nicholas Soames, MP for Mid-Sussex, said: "It is very good news. The Gatwick Express is absolutely vital but it is also vital to have more capacity all along the line.
"We are woefully under-invested as far as infrastructure goes. I hope the hard-pressed commuters, who have a tough time of it every day, will notice a difference as soon as the service goes ahead."
Trains from Brighton to London carry 25 per cent more passengers between East Croydon and London than they should. Gatwick Express trains, meanwhile, are on average only 43 per cent full at peak times which led to plans to scrap the airport link.
The London to Gatwick airport route - used by millions of holidaymakers travelling to and from the West Sussex airport - could have been axed under new rail plans.
But the Department for Transport said the service would be retained as a non-stop route and would keep its 15-minute frequency.
At the busiest times of day the service will also run beyond Gatwick to Brighton, doubling the number of express trains between Brighton and Victoria station in London in peak times. Some services will call at intermediate stations including Preston Park, Hassocks, Burgess Hill and Wivelsfield.
Unused coaches will be taken from storage and reconditioned to provide the extra trains.
Christine McLean, councillor on Haywards Heath Town Council, said: "In principle it seems like a good idea and will be welcomed by all our commuters.
"Anything that helps with the overcrowding and encouraging public transport which helps the economy has got to be good."
Brighton commuter Ann Noon, who works in Haywards Heath and often goes to London and Gatwick for meetings, said: "Anything that gives you more choice has only got to be a good thing - I would defintely be in favour.
"If there were more trains it would be easier to get to Gatwick for early morning flights to meetings and generally make travelling easier."
The changes will provide more than 3,700 seats into and out of London at the busiest times.
It was also announced that an extra 48 carriages will be made available on the Thameslink route operated by First Capital Connect (FCC). The first 16 are due to begin operating on the line, which runs from Bedford to Brighton through Central London, by the end of 2007 with all 48 in place by December 2008.
This allows FCC to double the remaining four-carriage services to eight carriages during the peak. As a result, the company says it can add almost 8,300 seats during the busiest times.
Transport Secretary Douglas Alexander said: "Not only are we adding more seats and more trains on some of the country's busiest rail routes, we are also keeping the fast, frequent Gatwick Express. We have done this by making better use of track space, taking carriages out of storage and approving the building of new trains."
Figures published by The Argus 17 months ago showed that 5,833 of the 75,228 people crammed into Southern carriages during the average week-day morning peak period were on trains already officially classed as full, with many commuters forced to stand for the length of their journey.
The capacity of modern trains for standing passengers is 35 per cent of the number of seats meaning that the average carriage is overcrowded and carrying excess passengers once 65 have taken their seats and 23 more are standing.
Gill Mitchell, head of transport at Brighton and Hove City Council, said: "This is overall good news for Brighton in that we have got extra trains to London and new rolling stock.
"It is good news not only for commuters but for the city's economy. A good efficient transport system is absolutely key.
"The council did not want to see the Gatwick Express saved to the detriment of commuter trains but they seem to have come up with a balance. We have got some extra trains while retaining Gatwick."
The new arrangement means that National Express, the current operator of Gatwick Express, is losing the franchise which will now become part of Southern, a joint venture between the Go-Ahead Group and French-based company Keolis.
Mark Froud, chief executive of Sussex Enterprise, welcomed the announcement on saving the Gatwick Express.
But he added: "We are concerned that extending the service down to Brighton will do little to ease the problem of commuter congestion.
"It is a short-term fix which looks good on paper but won't work practically. Mixing commuters with air passengers just won't be effective as they have completely different needs.
"Instead of trying to squeeze out more capacity by tampering with the Gatwick Express service the Government should be thinking on a much larger scale and be looking at radical plans to upgrade the entire rail infrastructure."
Shelley Atlas, chairwoman of the Brighton Line Commuters, said: "Obviously any extra express trains are going to be good for passengers as long as it doesn't have an impact on intermediary stations.
"It is important to monitor how things go and update services according to how they are used and how other things are affected."
Passenger Focus, the independent national rail consumer watchdog, said: "It is good news for commuters travelling directly from Brighton and Haywards Heath to Gatwick and London who will benefit from the Gatwick Express trains.
"However, it is not clear how the new plans will impact on passengers at intermediate stations and we would like assurance that commuters along the line will not lose out as a result of the changes."
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