Dr Smith has vetted international travel by other MPs, other than those on official trips, since he abolished the use of their taxpayer-funded discounts for private journeys. MPs can still get the discounts if the Speaker agrees their travel is work-related.
Dr Smith said that while in the US, he would try to ensure New Zealand's desire to move on with the TPP was not ignored as Washington dealt with America's economic problems.
"New Zealand is keen to make progress on that leading up to Apec this year to see if it's possible for President Obama to say something about it at Apec."
Dr Smith hoped he could "open doors" for New Zealand using his position in New Zealand and the officials and politicians he knew from the 1990s, when he, too, was involved in Apec.
Prime Minister John Key said Dr Smith's contacts from his time as trade minister would be useful, and he indicated Dr Smith was dispensable on the election campaign. "It is probably not appropriate for him to campaign given he's the Speaker, so it seems a good use of his time."
Labour MP Trevor Mallard also said Dr Smith's travel was appropriate, given the level of bipartisan agreement on the TPP. Dr Smith would have some influence, given the importance of the role of the Speaker in the United States and Dr Smith's background in trade.
However, he could not resist adding a dig about speculation Dr Smith will be offered the plum diplomatic posting of high commissioner in London in the next term.
"I'm working on the basis that he's actually going to London, not Washington DC, to look at the house."
Dr Smith said he was not tagging holidays to the end of his trip.
Greens co-leader Russel Norman said he had no objections to Dr Smith travelling to do business. "We want New Zealand to be part of the world." However, it was inappropriate for the Speaker to be promoting the TPP.
"Surely the role of the Speaker isn't to get involved in partisan politics and not everyone in Parliament agrees with what National and Labour are doing," Dr Norman said.
Dr Smith heads an official "Speaker's Tour" each year, taking some MPs overseas. In January, he is also expected to attend a meeting of Commonwealth Speakers.
Dr Smith said he had cut the costs of running his office by about 50 per cent since becoming Speaker in 2008.
THE ITINERARY
Where: Washington DC
When: October 11-19
Flights: $20,000-$30,000 (estimated business-class return flights for Dr Smith and staff).
Accommodation: Mostly at ambassador's residence with Mike Moore.