A system of cameras used to track traffic on major Long Island roads is back on line after being knocked out by a computer glitch for about four hours Thursday, the state Department of Transportation said.

The informny.com system outage came around noon, just before the start of one of the busiest traffic holidays of the year, the Fourth of July.

The glitch was on the server, DOT spokeswoman Eileen Peters said. The cameras were returned to service shortly after 4 p.m., she said.

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She said the problem only affected people who wanted to view traffic on the website and did not affect the overhead message boards along highways or the automated alerts sent to people who sign up for them.

"It's just the people who would look at the Web before they leave on a trip," she said.