Bridge at Midnight (contributed by Denis Borris) Eleven people on a war
games weekend come to a railroad trestle. It is midnight and there is
no moon. Crossing is very dangerous because the ties are slippery and
unevenly spaced, but they need to get over in the shortest possible
time. The people are of widely differing ages and fitness. The time it
will take the people to cross is 5, 10, 15, 20, 30, 30, 35, 45, 50, 55
and 65 minutes, respectively. Each person knows everyone's time.

They have just 2 small flashlights, and each one casts only enough light
to allow two people to cross safely. Whenever 2 people cross together,
they cross in the time of the slower person.  Once they begin crossing,
both flashlights are in constant motion, being carried across and back
on the bridge. They are never held waiting for someone to arrive. The
flashlights can be handed off at either end, but not part way. Crossers
never turn around or stop on the bridge. The last sets of crossers all
finish together. Also, the two people who need 30 minutes hate each
other and will not cross together.

How long does it take for everyone to cross? How is this accomplished?