I wrote on Friday about how random sobriety checkpoints were not only unconstitutional searches, but were also ineffective.  The only reason that police organizations support them is because it allows them to randomly search for other things (drugs, people without licenses, etc) without needing probable cause.  They're simply taking advantage of people being afraid of drunk driving, to leverage more power for themselves which they normally would not be allowed to have.

Of course, drunk driving is not the only scare tactic that police organizations use in their attempts to get around the 4th Amendment.  In Washington D.C., they're using terrorism as an excuse to randomly check people's backpacks:

Metro officials announced today that they will begin randomly inspecting backpacks, gym bags and any other containers that riders carry with them onto the bus and rail system, in an effort to deter possible terrorist attacks.
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The inspections will take place when transit police determine that circumstances -- such as an elevated threat level -- warrant heightened vigilance. They will not be announced ahead of time. Inspections will be conducted by five to eight specially trained Metro Transit police officers and a police dog trained to sniff for explosives.
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In the searches, transit police will choose a random number ahead of time, such as 17. Then they will ask every 17th rider step aside and have his or her bags searched before boarding a bus or entering a rail station.

Police said the inspections would take between 8 to 10 seconds. Those who refuse will not be allowed to enter the system with their carry-on items but will not be detained.
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If transit police find illegal items such as drugs, the item will be seized and the person will be arrested. But Metro officials today emphasized that the purpose of the search is not focused on drugs or contraband.

This is essentially the same as a sobriety check point.  There is no evidence to suggest that this will have any effectiveness.  What if the terrorist is the 16th individual in line, and not the 17th?  Oh well?  More importantly, this would only catch stupid terrorists.  If they have a bomb in their bag, and are stopped by the police, they are allowed to refuse the search, and walk away.  So all the terrorist would then have to do is wait half an hour, or go to a different train station and then try again.  The odds are with him that he won't be the 17th individual (or whatever random number they choose) the second time, and so his attack will still be successful.  The cost of failure for a terrorist attempt is zero, while the cost to us for trying to stop terrorism is high, and we have to be perfect and lucky every time.  It just doesn't make sense.

At the same time, we will have pulled individuals away from other jobs where they might be more effective.  Those people manning the checkpoints would do better looking for suspicious behavior or detering crime that is more common on train systems like theft.  But of course, if we happen to catch someone with drugs in their bag during our illegal searches, we will arrest those people.  But hey, we're really doing it to fight terrorism, not drug use, so that makes probable cause requirements go away by magic.

Via Reason.