ryanov wrote:What kind of accident, for example, could result from this particular violation? Are there any previous examples?
When a train is delayed in the block, the protection provided by the signal displayed upon entering that block is compromised. In other words, conditions may have changed during that period -- such as a switch has been opened, and/or a train has occupied or fouled that track.
(Note: in-cab signals that continuously display the condition of track ahead are the best way to avoid the need for restricted speed when "delayed in the block.")
That's where the "track is known to be clear" portion comes in. If one can visually observe the entire length of track up to the next signal displaying a signal to proceed, then it's safe to increase above that speed requiring the ablity to stop within half the range of vision, etc..
I can't cite specific accidents from this violation, but I'm certain there have been many.
The only "banners" I've ever seen were large, bright orange objects that couldn't be missed if the crew were to be vigilant ahead as required by the rule. FRA initiated this test after determining that there were inadequate methods in place. Previously, officers would simply shoot radar and confirm that speed was below 15 mph -- not a true test of being able to stop short!
All of this is similar, but not the same as speed limts on roads for automobiles. Keeping trains from colliding with each other (which has happened far too often over the years, and continues to happen!) is the main point of these procedures. Stopping quickly is impossible at normal speeds, and there is no steering mechanism for avoiding an object on the track ahead.