Why do trucks stop at weigh stations?
To weigh in to make sure that they are not overloaded (because they causes more stress on the roads sometimes in towns at stop lights and stuff you can see the grooves in the tarmack were the trucks come through alot)
Yes, all commercial trucks must enter all weigh stations. Execpt most newer scale houses are all electronic, so if your weight is ok you might get the by pass light and just keep going. If your weight is close to the limit, they will have you pull on the scale to check your weight. Being overweight can be very expencive.
Official weigh stations are operated by the highway department for the enforcement of laws relating to maximum load limits and have no services available to the general public. (It's a bit like asking if you can buy donuts at a police station.) However, it's not uncommon for "truck stop" type service stations to have unofficial scales for drivers to check their load to make sure they're within the legal load limit.
A semi-truck driver can only drive for 11 hours per day. Their total day is allowed to be 14 hours, however 3 of those are waiting to be loaded or unloaded, getting gas, or getting food. Log book are to be kept up to date and completely accurate at all weigh stations, or if an officer asks to see them.