How they are powered.

The speed.

The cost as well as the power needed to operate..

A CAR HAS FOUR WHEELS ,A BIKE TWO WHEELS ,AND A TRAIN A LOT  OF WHEELS,

Where they drive. A train runs on tracks, bicycle runs on sidewalks or paths sometimes the the road, and a car drives on the street or highway. Unless you've been drinking to much.

the size

Time has allowed technology to improve the function of all three of them in efficiency, manufacture, and materials they are produced from. All of them are far removed from how they were originally designed, as many of the original models were known for injuring their operators to varying degrees, in ways that are for the most part forgotten about these days.

Size, weight, power, speed, brakes, wheels, lights, horns, acceleration, fuel quanity, length....etc.

Oops double gator, thanks hector...

A bike is manual powered and the various models mountain etc. The train system in the U.S.A are intercontinental track systems and the trains powered by diesel engines.The typical passenger car 4 wheels 4 to 8 cylinder internal gasoline motor  and the 18 wheeler semi tractor trail diesel powered vehicles

Nothing really , they all need a human being to operate them.

You might like to know that a 100 year old Frenchman covered almost 25km in an hour on a bicycle recently. Though I suppose his bike was not 100 years old.