The problem is likely to be a dull drill bit.
That guard rail is most likely made of mild steel that has a Rockwell
Hardness of about Rc5. Your drill bit looks like just a high speed
steel bit, and it's got a hardness of about RcP or so. So, if that
were a sharp bit, you should have made some progress.
If you were wanting advice from me on buying a new SET of drill bits,
I'd tell you to buy a set of cobalt steel drill bits. These are the
brownish coloured ones that look like this:
Cobalt steel bits provide for the best economy because they're made from
a considerably harder kind of steel than high speed steel. Cobalt steel
has a Rc hardness of about 65 or so. That results in the drill bit
dulling slower than a HSS bit. And, if you dull a cobalt steel drill
bit, you can have it sharpened, and you've effectively got a new drill
bit for the $2 or $3 cost of sharpening it.
But, for a one-time project like this one, my advice to you would be to
buy a titanium nitride coated drill bit of the size you need. Titanium
nitride coated drill bits are the gold coloured ones that look like
Titanium nitride coated drill bits are nothing more than high speed
steel drill bits with a SUPER hard coating on them. The hardness of
that titanium nitride is about Rc = low 80's or so; 81, 82, 83 maybe.
But, that's vastly harder than anything else on the market so titanium
nitride bits will make the fastest progress and get dull the slowest.
For a one time project like this, I'd pay a few dollars for a titanium
nitride bit in the size you need, and just chuck it once it gets dull.
You CAN have titanium nitride bits sharpened, but sharpening them grinds
off the super hard titanium nitride cutting edges at the front of the
bit, so you're effectively left with a sharp high speed steel bit that
will dull just as quickly as any other high speed steel drill bit.
And, as previously suggested, I'd use a cutting oil if you have any. If
not, just stop frequently and use a Q-tip to apply any kinda oil (even
cooking oil or engine oil) onto the hole you're making. That'll help to
keep the drill bit cool.