1/2" laminated glass will block a lot of noise but its expensive and dangerously heavy. There is little point in adding that much glass unless you are in an otherwise quiet masonry structure. I would just use acrylic. Its cheaper and lighter and blocks a lot of noise too. You can attach it with a magnetic strip to make it easy to remove.

Your window frame will likely not handle that much weight so you will need to secure it to the studs under the frame. As for caulk, most of the acoustic sealants are nasty. I would just use silicone. The objective is to put as much mass between you and the noise source as possible.

Take a look at the photos on www.soundproofwindows.com that might give you some ideas. Also, there is a lot of useful additional information on www.soundproofing.org.

You may also want to write your congressperson to complain about the ridiculous standards set for vehicle noise. No, trucks do not HAVE to make anywhere near the noise they do.

I agree that 1/2" laminated glass can be very heavy and can be very expensive.

Plastics (acrylics and polycarbonates) have about 1/2 the sound blocking ability of the same thickness of glass but they will affect a different frequency than will glass at the same thickness so that that may be advantageous depending on the frequency of the annoying sounds.
One advantage of adding an interior window will be that it creates an airspace between the added lite (of whatever material) and the original window. If that airspace is tight, then you will gain a good deal of sound attenuation from it.

I am still curious if the homasote (that you mentioned in your previous post) had any effect on the sound coming into your bedroom? I am still wondering if you might have an installation issue with your replacement windows.

I'm considering making interior storms as well by next year primarily to cut down or largely eliminate infiltration and add some more insulation value. The various commercial products are amazingly expensive so was considering making them myself.

Depending on the layout of your residence, you also have to keep emergency egress in mind when designing the interior storm windows. If your counting on a window as one of your two paths of egress, the interior storm has to be fast and simple to remove. Regarding glass, I worry that that the storm unit can end up being fairly heavy for our young kids to handle by themselves so plastic is probably a better choice.

I'm thinking exactly the same solution too. But my problem is slightly different. My house is back to a school's playground. The small kids are all over the place during their breaks. So the noise is mostly higher frequency.

Oberon, you mentioned that acrylics will work well on blocking a different frequency, so would it be a better material for my case? I've sent you a separated email. Thank you in advanced for any help you could provide.

Traffic noise is generally low frequency - human voices are higher frequency.

Plastics can work fine as an interior storm primarily because they will allow you to build an airspace between the exisiting window and the plastic sheet.

The wider this airspace, the better the sound control - provided that the window is the path of the noise and that the interior "storm" window is sealed as tightly as possible when installed.

As gordonr suggested, keep in mind egress when considering any window modification. If you have to get out quickly then sound blocking ability becomes a very unimportant consideration.

Laminated glass can be very difficult for anyone to get thru quickly, and even trained firefighters can have difficulties with it.