Avoid forcing users’ browsers to open links in new tabs/window.
As a rule of thumb, it is best to give site users as much control as possible over their experiences of your website. The default user experience with links is that users can open a link in a new tab manually if they desire. Forcing links to open in new tabs through HTML code takes control of the site experience out of your users’ hands. This is one reason that the Washington University web standard is not to force links to open in new tabs.
The definitive reason not to force users’ browsers to open links in new tabs/windows is that it creates an accessibility issue. For users accessing your website via assistive devices such as screen readers, a link that opens in a new tab can cause confusion. Because users with low sight or cognitive disabilities may not be able to identify when a new tab opens, opening in a new tab “breaks” their back buttons and disrupts their experience of your site. If links open in new tabs, it is necessary to alert users. Current browsers do not perform this function. It is possible to force links to open in new tabs if you provide a notification method in addition to visual cues, such as typing inside the link text a cue like, “(opens in new tab).”
Additional Perspectives on Opening Links in New Tabs
http://www.nngroup.com/articles/multi-tab-page-parking/ (See end of article.)
http://www.nngroup.com/articles/top-10-mistakes-web-design/ (See #9.)