Track bikes are not very good for onroad use.
Track geometry tends to be very upright with angles of 75º or more and have very short wheelbases. This makes the bike very twitchy when it comes to handling, and if you aren't used to it will more than likely make you end up laying on the ground if you aren't concentrating. They also tend to be, well, fragile. Remember, track bikes only make left turns and are only used on closed courses.
The most common difference between a single speed and road frame is the rear wheel spacing. Most [modern] road wheels have rear hub widths of 130 or 135mm while most single speeds have 120 or 126mm widths. No, you can't just put in a single speed wheel and "squeeze" the frame... this will upset the chainline and if the frame is made from anything but steel could possibly- make that probably- cause catastrophic frame failure.
A steel frame can be PROFESSIONALLY reset to the correct width, but by this time you'll have spent enough money to buy a new bike.
There are hubs that have taken the width issue into consideration, and there are a few frames that have dropouts that can be swapped out (strange but true) to "make up" for the different widths. Again, I would research the cost of a new bike versus the cost of redoing an old one.
Track geometry tends to be very upright with angles of 75º or more and have very short wheelbases. This makes the bike very twitchy when it comes to handling, and if you aren't used to it will more than likely make you end up laying on the ground if you aren't concentrating. They also tend to be, well, fragile. Remember, track bikes only make left turns and are only used on closed courses.
The most common difference between a single speed and road frame is the rear wheel spacing. Most [modern] road wheels have rear hub widths of 130 or 135mm while most single speeds have 120 or 126mm widths. No, you can't just put in a single speed wheel and "squeeze" the frame... this will upset the chainline and if the frame is made from anything but steel could possibly- make that probably- cause catastrophic frame failure.
A steel frame can be PROFESSIONALLY reset to the correct width, but by this time you'll have spent enough money to buy a new bike.
There are hubs that have taken the width issue into consideration, and there are a few frames that have dropouts that can be swapped out (strange but true) to "make up" for the different widths. Again, I would research the cost of a new bike versus the cost of redoing an old one.