Hail All! 
Sorry if this seems a little OT, but for what it's worth I thought that I would post it anyway...
I see the old seat belt chestnut has been brought up again by people elsewhere:
They have obviously forgotten about this report:
Airline-style seatbelts on trains could cause more injuries to passengers than they prevent, rail experts have said.
http://news.bbc.co.uk/1/hi/uk/4542952.stm
I noticed this being the standard view on Greyhound buses when I was in the U.S. earlier this year. Anyone who uses National Express will know that most/all of their coaches have seat-belts fitted, which I personally use whenever they are available. When I got to the U.S. and rode on a Greyhound for the first time, I mentioned to the driver before departure my concerns at having no seat-belt available, where he cited the common opinion in America that coach passengers are safer
without airline-style belts.
From what I know about physics etc, the seat-belts on aircraft are
not so much intended to protect passengers from injury in the event of an emergency landing or head-on collision (With an airport vehicle etc.), but rather designed to keep passengers safely in their seats. Commonly, this is during take-off (In the event of a bumpy runway or irregular ascent), landing (Where up to 2G of forward force may be exerted on passengers), and turbulance (Where passengers may experience up to -1.5G of "airtime", as we call it in the rollercoaster enthusiast community)...Although they do contribute to passenger safety in the event of an emergency landing and thus should be worn whenever possible.
Looking at the differences between "airline" and "car" style seat-belts in a normal 60mph collision (Where a forward force of up to 8G may be exerted on objects inside the vehicle) a "car" style belt holds the passenger in their seat at the lap, but also keeps the torso on the back of the seat with the sash portion across the chest.
Conversely, "airline" style lap belts do keep the passenger in their seat, but as there is no torso support the passengers upper body will be thrown forward, leading to the passengers head making contact with any objects (Dashboard or seat back) that are in front of them. Aside from the obvious head and upper body injuries that this can cause, there is also the scope for injuries at the waist caused by the belt "cutting" into the passenger, and possible spinal damage or seperation at the lower back due to the forward force of the unrestrained torso against the restrained waist area.
If seat-belts were fitted onto trains, I would use them there as well...Although for the reasons and explanation that I've outlined above, I think that a three-point belt would be a much better option than a lap-belt.
However, the obvious impracticality of this is that not only would the train be heavily delayed through staff checking that passengers have their seat-belts on before departure, what would be done about standing passengers on busier services? Anyone who's ever used a Sunday afternoon service from Birmingham NS to Euston will know how crowded the train can get most of the time, which sometimes results in First Class being declassified and standees throughout the length of the train.
Back in the 80's, BR had a "no standing" rule in force on their APT services. That may have worked back then (Wasn't the APT a reservations compulsory service?) but it wouldn't work today due to the increased number of passengers using the network in a "walk up" fashion.
Finally, there would be the additional problem of seat belts wearing out quickly in heavy use by passengers, and the associated extra maintenance costs and vehicle downtime involved in installing/replacing seat-belts.

hock:
To make a quick-ish summary:
I'm personally not too bothered about having no seat-belt when I'm on board a train, although if they were fitted I would use them. I feel that three-point belts are safer than two-point ones.
However, my tip for increased safety (At least against a head on collision) would be to choose a rear-facing seat. Should the train come to a sharp emergency stop, your body weight (Remember that it would be up to eight times higher than normal) would be pushed back into the seat and the weight would be placed upon your back, which is better designed to widthstand such compression forces than the front.

Personally I prefer to face forward when I'm travelling, but I usually keep one restraining hand on the table or back of the seat in front so that in the event of a collision I can restrain myself. My arm will only widthstand up to 4G of forward force though.
(As an additional side note, this is why the DSA recommend that drivers hold the wheel in the "ten past two" or "quarter to three" positions - This would allow the driver to brace themselves against the wheel in the event of a collision. An especially important tip for drivers of older cars like my own that do not have air-bags fitted.)
Farewell, and pardon my ramblings!
>> Death <<