To reduce build queues, you can add build slaves. The master server will send builds to the slaves based on a round-robin scheme or tie specific builds to specific build slaves.
The reason for this is usually that some builds have certain requirements on the host OS.
Build slaves can be used to increase the efficiency of parallel builds. They can also be used to build software on different operating systems. For instance, you can have a Linux Jenkins master server and Windows slaves for components that use Windows build tools. To build software for the Apple Mac, it's useful to have a Mac build slave, especially since Apple has quirky rules regarding the deployment of their OS on virtual servers.
There are several methods to add build slaves to a Jenkins master; see
https://wiki.jenkins-ci.org/display/JENKINS/Distributed+builds.
In essence, there must be a way...