That depends what you mean by "security." As I have posted many times in the past, unless we search each and every person traveling in and out of Grand Central Station and Penn Station, there is absolutely nothing that can be done to stop an attack, whether it be a suitcase nuke, backback dirty bomb, or a briefcase packed with conventional explosives, unless you have advance intelligence of the who, what, when, and where, and stop the attackers before they even step foot in the station. Nearly a million people travel through both Grand Central and Penn Station each work day. That's nearly two million people that would need to be searched or profiled. ME types easily blend in with the dozens of other ethnic groups that use the mass transit system during the week. Although so-called security might be a bit more relaxed on a Sunday (although not much from my observations), ME types would be more, not less visible on a Sunday because the traffic through Grand Central and Penn Stations on a Sunday is measured in the thousands as opposed to millions.
Did you see MnC's post about Sunday in London?