Thanks for the input Hubeeo and Jim.
Indeed, I don't want the scenario to be to much of a railroaded affair. For the moment I'm going to let the bridges be destroyed from the start of the scenario. I am however still putting in some defend objectives (with occupation points) at the bridges that end at the time they would have normally been destroyed. This way I'm still putting in some kind of incentive to go there and clear out the area of any troops, while still being rewarded for doing so.
Indeed, I don't want the scenario to be to much of a railroaded affair. For the moment I'm going to let the bridges be destroyed from the start of the scenario. I am however still putting in some defend objectives (with occupation points) at the bridges that end at the time they would have normally been destroyed. This way I'm still putting in some kind of incentive to go there and clear out the area of any troops, while still being rewarded for doing so.