Kind of a shot in the dark here, but here it goes.

Find the initial speed of the train by figuring out what speed the train would need to travel in order to turn that extra 100 miles it gets in the second scenario into 1.5 hours of shorter time,

i.e. how fast must the train travel to go 100 miles in 1.5 hours:

100/1.5 = 66.6667

Initial speed of train = 66 2/3 mph
After Accident speed = 66 2/3 * 3/5 = 40 mph

D=R*T

D= 66 2/3 * 1hour + 40 * 3hours (ignoring the one hour layover) = 186 2/3 miles

Here we have the time difference of 1.5 hours because of difference speed with which the train travels to cover 100 miles.
Let the initial speed of the train is v.
So we get 100/(3v/5) - 100/v = 1.5
this gives v = 400/9. Hence the initial speed of the train is 400/9
Now let the total time taken for the journey (assuming no accident) is t
Equating for distance
400t/9 = 400/9 + 80(t-2+3)/3

This yields t = 4 hours.
Hence the total journey is 400*4/9 = 178 miles approximately.