Latest version of IR, UMC, Track API

This video (with timestamp) shows the previous behavior of speed retarders prior to the latest 1.8.0 release: https://youtu.be/-tj8MqKKVf0?t=139

In the current release version, the train's velocity is not noticeably impacted by the activated speed retarders, and it simply continues past the braking section with only marginal slowdown which can be attributed to the rolling resistance of the consist.

You can replicate this by just setting up a straight rail, with some speed retarders in the middle activated with redstone, and drive the train past this section.