Bus riders, watch that one step when you exit.

The MTA’s new “low-floor” buses are causing straphangers to stumble, with the number of accidents rising 7 percent in 2009, compared to 2008, NYC Transit officials said Monday.

People assume the bus is the same level as the street and then trip on the sidewalk, said officials, who reported that most of the accidents occur at the front door.

“We unexpectedly introduced a bus without steps, and we wind up having more accidents,” said Joe Smith, senior vice president of buses for transit.

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According to an MTA study, only 5 percent of riders on the system’s 1,800 low-floor buses hold on to the door handle when they get off, as opposed to 90 percent of those leaving buses with stairs.

The MTA is also rolling out a public education campaign to tell riders to watch out for that step.