So I've been doing the bike commute for about 2 years, with some stretches of driving because of my bike getting stolen.
And I've seen the same people over and over again riding the train with me and then I've seen some people who got frustrated and returned their bikes to the dustpile. The thing is, ten years from now, I probably can't be as effective of a voice as I can be now because some of it is still very much new to me too.
I can assure you that, especially if you've been living a fairly sedentary lifestyle, it's at least 50 times better than you think it is. Here are some things you should be aware of:
I started out around 240 pounds and reaching new levels of out of shape. But on the Bike forums, there are people who needed supplemental oxygen so they started biking with a tank strapped to their back. The thing is, the bike is one of the most efficient ways to convert human energy to motion. So if you can still walk, you can probably bike and even reach a fairly decent speed.
Give it a year or two of commuting regularly, and you'll be shocked at how far and fast you can bike.
So I started out, pretty out of shape, and started biking 5 miles. I started every other day and then worked up to every day. I've gotten progressively faster over time as my muscles have gotten better and I've figured out how to adjust my bike better, so after a few months, it was not a big deal to ride.
Hills are the same way. You might start at the foot of a hill and wonder what the hell you are doing trying to climb. Do that hill every day for a year and it'll be easy.
Everything gets easier. The racks on VTA light rail are actually fairly awesome as far as getting a bunch of bikes packed into the car without cutting too much passenger capacity and without getting the bike wet in the rain or anything not welded to the frame blown off. The first few times, it sucks to use them. After a month or so, I've got muscle memory and I can do it while the train's jolting with astonishing ease.
When you start to look at the time you will spend behind stop signs or at traffic lights, you start to realize just how much time your car spends sitting doing nothing. So I've found that it doesn't actually take me that much longer to get to work via bike than it does to get there via car.
It takes me two to three times as much time to get to work via bus than it does via bike.
In the end, the extra time I spend on the bike is offset by the added energy I have over the rest of the day and that I'm getting an astonishing amount of exercise but not actually needing to spend an hour or so in the gym every day.
It turns out that any decrease in lifespan that you are subjecting yourself to by not having a metal cage around you to protect you from other cars is well offset by your reduced likelihood of developing Type 2 Diabetes, having a stroke or a heart attack, or other such obesity and inactivity related health problems.
So, everybody can do a few miles... but you don't live a few miles from work, do you?
In Silicon Valley, we've got a fairly spotty transit system. We've got a bunch of really useful pieces of infrastructure... mostly rail lines. But down where I live, there's not enough density to have reasonable bus or trolley or train service across the whole area. But I'm 5 miles from a train station and the trains start early and run late.
If I didn't bike, I'd have to keep a very tight schedule that I simply cannot keep in order to get home without a car or without walking those 5 miles because the bus stops running too early.
Most transit systems have lines with better service that you can bike to. Or train stations. Or maybe you can bike to a friend's and carpool. I have always been either five miles from my job or five miles from a useful transit point. Even when I lived in the midwest. Plus, your grocery store and probably some of your other regular errands are also probably five miles away.
For five miles, anything will do. As long as it works and has a seat, of course.
You may already have a bike in your garage. Or maybe your friend has one they don't use and want to get rid of. Even if it's old, you can still replace broken parts and make it ride just fine.
I tend to think that Wal Mart and other similar places aren't so good for getting a bike. The big problem is that bikes are shipped disassembled in crates and they will be assembled by somebody who may or may not know what they are doing and probably won't read the manual. So there have been some cases where they've really botched the assembly and somebody got hurt.
So it's better to go to a real bike shop. But there are other options. You can get somebody's unloved used bike. Even if you spend some money overhauling it yourself, you can still come out ahead. Or you can take advantage of the Internet and order almost-assembled bikes online.
There are a lot of different kinds of bikes out there and some of them are fairly expensive. You can evaluate them based on various characteristics.
Hipster folk tend to choose fashionable bikes like "cruisers" and "fixies". Cruisers are those retro bikes that look like a Schwinn from the sixties. Fixies are any style of bike, but with the simplest possible transmission. If they make you feel better about yourself, you can get one, but they aren't necessarily optimal for all forms of cycling.
Most bikes tend to be somewhere between "mountain bike" and "road bike". Mountain Bikes are designed to plow through all sorts of nasty, muddy terrain. They tend to have suspension to level out bumps and knobly tires and other features like that. They also tend to be very heavy and not as efficient on pavement. Road bikes are designed for biking long distances at high speeds on pavement.
There's a lot of room in the middle for a bike that's mostly like a mountain bike but is good on pavement or a road bike that's good off pavement. And realistically, many well designed road bikes can go on a lot of off-road pavement just fine.
The cheapest and most approachable decent bikes tend to be "Hybrid" bikes. This means that they are part mountain bike and part road bike. The exact percentages change depending on the bike. Sometimes they are little more than low-end road bikes designed so that you ride them upright with a flat handlebar. Sometimes they are mountain bikes with some of the features that you only need on rocky, muddy, nasty terrain removed.
On the very high end, most bikes tend to be oriented towards extreme usages. So you get a very heavy mountain bike that is meant for very hard off-road rides or a very light road bike that is oriented towards racing. Neither one is particularly useful for an average rider who wants to ride for fun and exercise and transportation.
It turns out that you really don't know what you really want out of a bike until you've been riding for a while, so it behooves you to get a reasonably inexpensive biking starting out and then see about replacing it with something fancier when you know exactly what you want.
If you are heavier, the big thing to remember is that you want to avoid carbon fiber or especially lightweight metal frames and make sure that your wheels are sturdy. The wheels should have 32 or 36 spokes each and be properly tensioned.
Cheap is also good because people like to steal bikes and the police generally do much about it, so you don't want to plunk down a bunch of money for a bike and then have it stolen.
The problem is, your bike is worth at least the price of one rock of crack. And if somebody steals a bike, they can ride it home. Even if you live in a nice neighborhood, there will be at least one kid who's rich parents cut off his allowance. And you should always lock the bike up. Even if it's on a third story balcony.
It might seem safer for it to be in the secured parking of your building or in a bike-room in the basement, but I'm not really sure about that. I'm at the point where I keep my bike inside the foyer of my apartment because I just don't feel comfortable any other way.
My figure of five miles is also notable because you can do it in street clothes without getting too uncomfortable. Most of the clothes are there because they looks sporty and because it comes in handy if you are biking 100 miles.
I have a theory that, the less you look like a hardcore cyclist, the better drivers will treat you. It's also nice to not have to spend money on it starting out.
Pretty much, you want to start out with just about nothing and then see what you really need. You can get a helmet if it makes you feel safer. If your hands chafe (mine did) you can get some biking gloves. If you keep getting your pants leg caught in the gears, you can get a leg-strap or just tuck them into your socks. If you want to ride longer distances, maybe a pair of bike shorts will come in handy. If you get really sweaty, there are tons of wicking shirts and pants made from wool or polyester or other fabrics that won't get wet and cling to your skin like cotton will. They even have nice dressy shirts and t-shirts made out of this sort of material, not just funky looking biker jerseys.
But there are women who ride in dresses and heels. There are men who ride in suits.
Given the cost of a bike and the cost of having somebody do it for you vs. the cost of keeping a car up, you really don't need to be able to do anything other than drag your bike to a bike shop when it breaks or starts to act flakey. You may want to know some basic repairs if you don't want to be walking five miles to the nearest bike store with a flat, but it's only as much as you want. You will still come out ahead fiscally.
You might look out while driving during a rainstorm and see a drenched cyclist and feel warm and cozy in your car.
Honestly, the only part that really sucks is when you aren't prepared for it. I've got a pair of loose-fitting fully waterproof pants and then a "Breathable" jacket that lets my sweat out so I don't show up just drenched from sweat instead of rain. If it looks like it might rain, I'll make sure I've got them ready to put on.
We've got fairly predictable and mild weather here. There's a rainy season and a dry season. But I know plenty of people who do bike in snowstorms.
On the other hand, it's also the case that if you skip out when it looks really nasty, you have still made far more impact on yourself and the environment than the person who drives to work every day. So don't feel too bad about it.