Lightweight bike-transporter bag

Edit: Realised that this might be in the wrong category. Thankful for directions if this is the case!

Hi I'm posting here to see if I'm trying to invent something that allready exists and to have som helpful criticism of my idea.

Basically I want bring my Bianchi pista with me on the commuter train and the subway. For this i need a bag that lives up to the following criterias:

1. Lightweight
   
2. Foldable
   
   

I don't really have any need of padding as there will be rough handling and it's more a way for me avoid the hassle from the MTR. Also the bag itself will only need to carried on the train and of the, so there is little use for good handles and suchlike

After having looked around and realising that the Cinelli bag seems to be discontinued, I have decided to buy some rip-stop nylon ( as per from here per example http://www.profabrics.co.uk/products/crisp-pu-coated-nylon-ripstop?variant=6809886467) and then adding straps to get a kind of big tote-bag(http://www.profabrics.co.uk/collections/nylon-webbing-outdoor-camping/products/traditional-weave-webbing-50mm?variant=5940930883)
. My plan is for them to loop around under the base of the bag to releave some of the weight from the ripstop fabric. To close it all up I intend to use self-adhesive velcro (http://www.profabrics.co.uk/collections/self-adhesive-velcro-outdoor-camping ) .

So the real question(s) is:

1. Does this bag already exist?
   
2. Are there any obvious faults in my?
   
   

Any input appreciated!