The fatal error defence only works if the charge as written on the ticket doesn't match the set fine or total payable written on the ticket. In this case the charge written on the ticket and the fines written on the ticket match so the fatal error defence that rodwarriors.ca is talking about won't work. What you are arguing is that you did not commit the offence you were charged with, speeding in construction zone when workers are present, because there were no workers there at the time. This is a reasonable argument to make, but you are going to have to make it at trial, you can't simply ignore the ticket and wait for it to be thrown out as you would if you were using the fatal error defence. So in order to win you are going to either have to present some evidence that there were no workers there that day or see if you can get the cop to admit it when you cross examine him at trial.
According to section 14.1 of the HTA workers do have to be present in order for the fines to double.
http://www.e-laws.gov.on.ca/html/statut ... 0h08_e.htm Penalty for speeding in construction zones
(14.1) Every person who contravenes this section in a construction zone designated under subsection (8) or (8.1) when there is a worker in the construction zone is liable on conviction, not to the fines set out in subsection (14), but, where the rate of speed at which the motor vehicle was driven,
(a) is less than 20 kilometres per hour over the posted speed limit, to a fine of double the fine set out in clause (14) (a) for each kilometre per hour that the motor vehicle was driven over the speed limit;
(b) is 20 kilometres per hour or more but less than 30 kilometres per hour over the posted speed limit, to a fine of double the fine set out in clause (14) (b) for each kilometre per hour that the motor vehicle was driven over the speed limit;
(c) is 30 kilometres per hour or more but less than 50 kilometres per hour over the posted speed limit, to a fine of double the fine set out in clause (14) (c) for each kilometre per hour that the motor vehicle was driven over the speed limit; and
(d) is 50 kilometres per hour or more over the posted speed limit, to a fine of double the fine set out in clause (14) (d) for each kilometre per hour that the motor vehicle was driven over the speed limit. 2005, c. 26, Sched. A, s. 17 (8).