They're taking the low road

This year, the Boston Marathon goes underground, if only for a couple of hundred yards during the final mile.

To ease the Back Bay gridlock that results from closing the Massachusetts Avenue intersection to traffic, the runners will proceed through the underpass instead of using the surface road.

''I guess you could say we've reached a new low," joked race director Dave McGillivray, who noted that the bottom of the underpass will be 1 foot below sea level, the lowest point on the course.

The impact on times, he said, should be negligible.

''We're only talking about a drop of 13 feet," McGillivray reckoned. After the runners emerge, they'll take the traditional right onto Hereford Street, which leads to the final sprint down Boylston.

The second leg of the new million-dollar World Marathon Majors series, which debuts here Monday, comes a week from tomorrow with the London race, which has assembled the greatest men's field of all time. Besides Olympic champion Stefano Baldini, world titlist Jaouad Gharib, and the current (Paul Tergat) and former (Khalid Khannouchi) global record-holders, there's defending champion Martin Lel, former champ Evans Rutto, Chicago victor Felix Limo, former New York titlist Hendrick Ramaala, and double Olympic track medalist Haile Gebrselassie. ''It will be a bookie's nightmare," predicted race director Dave Bedford. Even with the late pullout of world champ Paula Radcliffe, the women's field includes former London champion and Boston record-holder Margaret Okayo, US record-holder Deena Kastor, and New York runner-up Susan Chepkemei.

How serious is the Hansons-Brooks team about its mass debut here? Besides coming in for a dry run on the course during the winter, they've been working out on a ''Boston Simulator" dreamed up by co-founder Kevin Hanson along the trails where they train in the Detroit suburb of Rochester Hills. ''I wanted them to be able to visualize where they are on the course," said Hanson, who rigged an ''Entering Newton" sign, among other landmarks. To simulate the stretch along Wellesley College, Hanson's 7-year-old daughter created a poster showing lingerie ads . . . This is a bumper year for Boston Marathon-related books, all published by Rodale. New to the shelves are John Brant's ''Duel in the Sun," about the classic 1982 showdown between Alberto Salazar and Dick Beardsley; ''The Last Pick," a motivational volume by McGillivray; and ''26.2 Marathon Stories," by Kathrine Switzer and Roger Robinson, an illustrated history of the 26-miler.