Users can install runtime whether or not Office or Access are installed.
If a copy of Access is installed, the runtime must be a different version and is a separate download.
Contrary to widely held belief, it is sometimes possible to install both 32-bit and 64-bit Office on the same workstation.
For this to work, install a newer 64-bit version followed by an older 32-bit version (either runtime or full)
For more info, see this lengthy thread where I investigated this in detail
UtterAccess.com.
I changed my long held opinion when I finally did some detailed tests
Based partly on my results, Mike Wolfe has just written about this topic at
Side-by-Side Installs of 32-bit and 64-bit Versions of Access (nolongerset.com).
I'm not suggesting you should install mixed bitnesses...but in certain circumstances you can do so...and it works without any issues.