Meditating on Public Transport
Is meditation itself possible/recommended on public transport?
Proper practice revolves around an integration of mindfulness meditation into daily life. Sitting (cushion) meditation practice is meant to develop mindfulness to such a degree that it can be transferred into daily life and ultimately into constant mindfulness until one can ultimately become free from Samsara. Walking meditation is another great way of bridging ones practice into daily life.
Meditation in gradually noisier environments will be challenging but that's the idea. If one only practices at home but can't use the practice outside of ones sitting practice, then it's not beneficial.
It's beneficial to meditate everywhere and all the time.
As an example; when I have patient consultation, I'm mindful of my abdomen rising and falling with each breath, the feeling of my lips moving when talking, the sound of my own voice, the seeing that goes on when seeing a patient, the feeling of pressure from sitting on a chair, the sound of birds chirping outside etc. One object at a time.
Even though it might be difficult to practice in public transport it should be done and with time it will become effortless. Don't worry about the quality it will become refined with practice. It's like learning to shoot a bow. With time and consistent practice one will finetune the movements, reduce energy consumption and eventually be able to do it effortlessly. It's the same with meditation practice in noisy environments.
At some point the mind will begin to incline towards being mindful due to the purity and simplicity of being in the present moment. When that happens there will be a strong momentum driving the mind towards mindfulness and away from unmindfulness. At that point it begins to become effortless. One does not have to apply and direct (vitakka and vichara) the mind anymore.
Would the quality of such meditation, if lesser, diminish the quality of general meditative practice?
No, never. It will build, develop, cultivate and add to "general meditation practice".
A doctor who specializes in a field will be good but a doctor who specializes in several fields will be even better.
A fighter who specializes in one school of martial arts will be good. A fighter who specializes in several schools of martial arts will be even better.