I'll wait for the next train rather than get on the crush carriage. I absolutely detest being crushed up against my fellow man - I need my personal space. I even get twitchy when someone sits next to me...

Traffic engineers, in our stubbornly technocratic ways, use a Level of Service rating (A thru F) based on density, similar to those used for traffic flow.

Of course, like anything else developed through academic empirical observation, there is no way to relate how much individual "transportation consumers" value the trade-off of cost vs. comfort.

In market-based transportopia, I suspect much of the LoS terminology would be banished in favour of "whatever people seem to want".

Or it would be banished in favor of what is most profitable for the roadway and transport network owners. Which I'm going to imagine will take the form of fairly high densities, ranging to roadway failure at least as frequently as the current roadway system. One environmental benefit might be that it would push people towards driving less, since direct payments for goods and services tend to make people less likely to use them than indirect payments.

Well, when we decide to travel first class (in either rail, or any other kind of transport) we are paying more money for more space, and for a few other things as well. Often we don't know how much space we are going to get when we buy lower class ticket. Second class rail travel is often fine when there are few passengers in the carriage, and not so when there are more. Similarly, flying a long distance on a Boeing 747 is far less unpleasant when you have a row of four empty seats all to yourself.

What we cannot generally do is change our class of travel and the amount of space we have on the fly depending on the level of crowdedness we discover on the day. Perhaps there is scope for electronic pricing systems that allow us to upgrade (and ideally also downgrade) as appropriate, even if we hold season tickets. Oyster cards and the like would certainly make it easier than with traditional ticketing systems.

I like Patrick's reference to passenger comfort or passenger space. The recent TV programe showing overcrowding on the Wimbledon to Blckfriars line is completely unacceptable. We should remember that some passengers like to stand, even when seats are available. The Southern Region of BR always had standing passengers in the peak hour, one of the worst lines being the Dartford Loop. The London Undergrond has always had crushed conditions in the cental area of London, not very pleasant. Public transport endeavours to respond to allow all walk on passengers to be caried. In this country, trams and buses have statutory load factors. It is interesting that this is not controllable on the new bendi-buses in London. Or is it?
Continental passengers have a different approach.
Trams departing from Basel Hbf, Zurich Hbf and Amsterdam are extremely heavily loaded in the morning peak after arrival of a train. However, the majoroty of passengers only travel up to three stops, and the remainder of the journey is in comfort. Also on the continent, the tram driver has no method of controlling the passengers joining, as motor and trailer cars have at least two doors. But everyone appears satisfied!. For longer journies in Germany, Holland and Switzerland, the trains are strengthened in the peak hours, and passenger 'comfort' is considerably better than in this country. Now we are back as to who Pays!
Before the introduction of open rolling stock in this country, the Regions of BR used a lot of compartment stock which gave the opportunity with 16 spaces in a compartment for most people to have a seat. Modern designs, and the desirability of using rolling stock to the optimum, and having fewer peak hour vehicles has led to more standing passengers and less passenger 'space' in this country. There is a depth of comon sense in Patricks' thoughts, which many in the industry should take on board.