First let me emphasize that the following is only a theoretical discussion
and should not be construed as a ruling. Please consult your local orthodox
It is important to distinguish between the prohibition of yichud and
situations which might be compromising but are not called yichud. Being
alone with a woman in a car at night on a public street is not itself
yichud. Driving off into a secluded area is yichud. Reb Moshe says he does
not allow a man and woman to be in a car at night since this might lead to
yichud - unless there is a pressing need.
He also discusses being alone in an elevator with a woman. Even HaEzer IV
#65.16 page 132-133. [see also #65.22 page 135] He states that if the time
of being secluded is less than the time for sexual relations there is no
prohibition of yichud...
This does not mean that a person does not have to concern himself/herself
about this seclusion - but only that a straight application of the
prohibition of yichud does not apply. A reasonable person - even outside the
framework of halacha - might not want to be secluded with a member of the
opposite sex - or even of the same sex (depending upon the neighborhood).
It is obviously reasonable for a person not to get on an elevator or accept
a ride in a car from someone to avoid the possibility of a compromising
In summary. Reb Moshe's ruling might better be expressed as - being alone
in a car at night is prohibited, without pressing need, because it might
lead to yichud. An elevator is not typically a violation of yichud and
perhaps the need to use it is considered a pressing need. One should try to
avoid all compromising or potentially compromising situations. Most of his
discussion is found in Even HaEzer IV #65 pages 127 - 135.
There is an excellent brief summary of hilchos yichud composed by Rabbi
Neustadt in his weekly parsha sheet provided by Project Genesis and I assume
available in their archives. It also mentions lenient opinions concerning
being in an car at night. It can be found at http://www.torah.org/advanced/
under Parshas Achrei Mos-Hilchos Yichud:Rulings of HaRav Feinstein.