I drive up Chilliwack Valley often and pass by that road. There is a sign posted near the gate which reads "Restricted Road, For Emergency Access, Contact ASU Chilliwack, Duty Officer 604-793-8638. For that reason, I don't risk driving up the road when the gate was open. Currently, the road has been gated for a while.
You can't call the number on the sign because there is no cell reception there.
The gate at the main entrance is for the fsr when logging was done but in the early 80's. It was not put there by the military.....they just use that gate. The actual military training area has its own gate about 7km up the road. The entire fsr is crown land and not DND land. They do restrict access when they do training but again, they don't usually just lock people in. If it was an unmarked trail it would be one thing but the Slesse trail is a designated recreation trail and again on Crown Land and it is reasonable to assume that people use this trail. I think if we just don't go on trails when incidents arise it encourages the further restriction of public land. Vancouver island is horrible for this (locked gates everywhere) and it really isn't right (in my own opinion)