I saw the Lac-Mégantic derailment disaster on youtube and wikipedia, I thought why are couldn't they have a simple heavy wheel chuck that it capable of totally stopping a train from moving down a slight incline- I don't think any sane engineer would stop a train on a serious incline. Something they bolt together in a few pieces and digs under the rails- sure put on a lots of brakes but this would make it impossible. Something made of steel that you could carry with you. Less risky than relying on many complicated subsystems that could have faults and fail. A quick search only found light weight wheel chucks that can't be relied upon for even one carriage. So why not a simple solution rather than needing 20 brakes to all work and the engineer to apply all of them ?
Several reasons.
1. A chock that is able to withstand the forces required to hold a unit train would simply be too heavy and cumbersome for practical use.
2. The forces required would damage the rail where the chock attaches to the rail.
3. If accidentally left unattended or trackside (as is likely due to the considerable heft) the chock would be an excellent way for vandals to derail trains at speed.
4. A chock would require the train to be backed away from the chock in order to remove it, which creates a serious problem if one man crews are used. (Engineer must back away train, stop it, get off, remove the chock, and get back on.)
5. Bolting on a chock would require more time and effort than applying a proper number of handbrakes.
6. Hazmat trains cannot be left unattended on steep grades anymore, as the rules have been changed.
7. Chocks cost money, and the handbrake system has worked well for more than a century with few runaways. It simply must be done properly.