+before can test
+ commands for speed manager
+ create data files containing some train data
+ write trivial initial settlement to get data array right
+ write out layout data on crash
+ check that everything in Train and Segment is init'd
+
+dunno but maybe before can test
+ train speed curve measurements
+ wiring to gui display
+
things not yet considered at all in safety code
- polarity
+ coming up against points the wrong way
min. curve specifications
+
+initialise safety_state with appropriate stuff