Rush hour traffic has caused long delays and eyewitnesses have claimed drivers are ignoring signs and travelling on the wrong side of the road.
One nearby businessman says the road closures mean the business is losing more than £40,000 a week.
A £214,000 project by Southern Gas Network to renew gas mains with modern polyethylene pipe started on Monday July 21 and the project looks set to continue until at least November.
Mill Green Road, which leads to Haywards Heath's railway station, has been closed for several weeks and businesses and drivers have expressed their frustration.
But gas works moved to Commercial Square on Monday and the situation has got worse.
Taxi drivers have witnessed most of the chaos as cars have been blocking up the station forecourt.
Francis Jennings, a taxi driver who works from Haywards Heath station, said: "People are coming under the bridge and not taking any notice of the road signs. I have seen a number of people coming up the wrong way and into the head on traffic, it is very dangerous.
"Commuters are very unhappy because taxi fares have gone up because of the long queues from the station."
Managers at the Elite Garage, opposite Haywards Heath station, say the situation is a nightmare.
Standing on the forecourt at 5pm on Tuesday, manager Chris Bhowler said: "Normally, there are ten cars here with every one of the pumps working – now there are three. I can't say exactly how much we will lose but it's going to be about £40,000 a week – possibly more."
The figure also covers proceeds from the tyre workshop where manager Kim Farmer said: "It's a nightmare. There's not enough work for everyone. We had to make our own signs and put them out by Sainsbury's to show people we're still open."

Full report in this week's Mid Sussex Times