Those sensors do fail, however.
http://globalnews.ca/news/2117570/alberta-oil-spill-when-fai... (2015)
Notice how many failure reports are not the sensor, but are due to humans checking up on the pipeline. The conditions these pipelines are installed in can be pretty hostile to equipment and monitoring. Going by those numbers, I'd say sensor systems have a ways to go.
The debate that usually goes around is that pipelines fail less often, but their failures tend to spill more oil, in more sensitive areas.
The other dimension, that isn't often talked about, is which transport system has the best chance to improve. Despite their current shortcomings, I think that a system that is dedicated to one job (moving dangerous fluids) has a better safety ceiling than shared systems, like trains and roads.
