I ran a Tobit regression model looking at the effect of temperature, phosphorus and nitrogen and location on algae units (upper limit of 85 units).

Code: 
library(VGAM)

summary(m <- vglm(algae ~ tn + tp + temperature, tobit(Upper = 85), data = tob))
Estimate Std. Error z value
(Intercept):1 -41.5109 14.63183 -2.83703
(Intercept):2 3.1699 0.13048 24.29450
tn 31.8145 17.04272 1.86675
tp 161.5168 192.94689 0.83711
temperature 4.1693 0.61760 6.75072
locationdownstream 29.8545 9.26552 3.22211
locationupstream 3.5800 9.09454 0.39364




Can some please explain what intercept 2 is?

I have seen it described as an ancillary statistic, but I am not entirely sure
what that means.