You have a couple of potential problem areas because the best ways to block sound are not necessarily the best way to block light (as you noted when considering shutters)and also, as you mentioned, you still want to be able to operate your windows easily even with a "sound blocking" solution in place. That may be difficult to achieve, unfortunately.
Please bear with me as I offer a few comments on window soundproofing. Hopefully, these comments will help you a bit when researching the best possible solution for your noise issue.
One consideration though. This is a large window and as such it will be a bit harder to quiet than a smaller window...but the information still applies.
Windows are rated as to their ability to deaden or attenuate sound based on something called an STC or Sound Transmission Class (walls and other building components use the same system, but here we are considering windows).
STC is an average of an objects ability to attenuate sound across the entire sound frequency spectrum. STC does not provide specific frequency-deadening information which is really what is needed if you want to block a specific type of unwanted noise; for example traffic noise.
As humans we are born with the ability to hear from approximately 20 to 20,000 hertz. Hertz, or Hz, is how sound frequency is measured - like electricity is measured in volts, for example.
By the time we are teenagers we have generally lost the ability to hear above about 13,000hz which as I remember is something mother always warned us about - going deaf - or was it stop or you'll go blind? I always get those confused.
Anyway, traffic noise is generally a low frequency sound, and unfortunately, low frequencies are much harder to attenuate (opposite of amplify) or block than are higher frequencies...consider how often you hear the bass sounds from the neighborhood kid's car stereo and not the higher pitch tunes when he is coming down the street.
When considering windows, there are generally three options available for maximum possible sound attenuation.
First is laminated glass.
Second is a wider airspace between the lites.
Third is different thickness lites within the IGU or Insulating Glass Unit.
Fourth would be a combination of all three.
Airport windows, for example, will often have laminated glass on both sides of the IGU in an aluminum frame and with a maximum width airspace between the lites. In an airport the primary concern is sound attenuation and energy efficiency is secondary. I mention this because the width of the airspace and the choice of window framing material affects both sound and energy efficiency.
Some folks will suggest triple pane glass for its sound deadening ability. And while triple pane is a slight improvement over standard double pane at lower frequencies due to the additional density of the extra lite, overall there is no difference in STC rating between triple and double pane provided that the overall airspace between the panes is constant between the two constructions. In other words, consider a triple pane with two 1/4" airspaces and a dual pane with a single 1/2" airspace...both using 1/8" glass...the STC will be identical if the IGU's are the same dimensions.
Using one thicker (3/16") and one thinner (1/8") lite in an IG construction will also help deaden sound because each lite is "transparent" to a different frequency and each lite will then attenuate the frequency that the other lite "passed".
Finally, a fixed window, as opposed to an operator, blocks more sound energy. Sound likes to find every little opening that there is in an object and then sneak thru that opening. An operating window has more little "openings" than a fixed window and that allows for greater attenuation of the sound.
Okay, lots of information, but is any of it a help for your issue?
You mentioned that you need an inside solution. An interior "storm" window made with laminated glass is generally the solution most people use. This solution offers a wide airspace between the exisiting window and the new lite, and the laminate also offers additional sound deadening ability. But, on the negative side, this solution does nothing for your light issue and also it is cumbersome to remove and store somewhere when you want to operate the windows.
The only other obvious solution that presents itself is to retrofit the existing windows with laminated glass as one of the panes of a new IGU. This solution may be less costly than you might imagine and it may help with the sound problem. But, the lack of the increased airspace as in the first idea will mean that more sound would get thru the windows than would be with an internal "add-on storm".