WASHINGTON • While few have noticed, United States airport security workers long had the option of using five types of physical pat-downs at the screening line.

Now, those options have been eliminated and replaced with a single universal approach.

And, this time, you will notice.

The new physical touching - for those selected to have a pat-down - will be what the federal agency officially describes as a more "comprehensive" physical screening, according to a Transportation Security Administration spokesman.

Denver International Airport, for example, notified employees and flight crews on Thursday that the "more rigorous" searches "will be more thorough and may involve an officer making more intimate contact than before".

"I would say people who in the past would have got a pat-down that wasn't involved will notice that the (new) pat-down is more involved," TSA spokesman Bruce Anderson said on Friday.

The shift from the previous risk-based assessment on which pat-down procedure an officer should apply was phased in over the past two weeks after tests at smaller airports, he added.

TSA screens about two million people daily at US airports.

The agency does not track how many passengers are subject to pat-down searches after they pass through an imaging scanner.

People who decline to use this screening technology are automatically subject to physical searches.

While passengers may find the process more intrusive, the new screening procedure is not expected to increase overall airport security delays.

However, "for the person who gets the pat-down, it will slow them down", Mr Anderson said.

The change is partly a result of the agency's study of a 2015 report that criticised aspects of TSA screening procedures.

That audit drew headlines because it found that airport officers had failed to detect handguns and other weapons.

An additional change prompted by the report was the TSA's decision to end its "managed inclusion" programme, by which some everyday travellers were allowed to use precheck lanes to speed things up at peak times.

BLOOMBERG