If you want to add bandwidth throttling on any one site, please follow my steps below:
1) Login your control panel of dreamhost. https://panel.dreamhost.com
2) Under main menu on the left side, click status.
3) Then click Bandwidth Usage. There is a list of your site per domain.
4) Click enable to enable bandwidth throttling with your own settings.
I have a 2TB Bandwidth usage capacity.
Currently I have a very small blog for my daughter, Grace. So, I give the limit to 30GB per month.
Dreamhost’s default setting is disable of bandwidth throttling. It will cost you much if you use over the limit. $1 per GB over.