In the United States, the vast majority of heavy trucks use air brakes. These brakes are far more effective than hydraulic brakes at slowing and stopping a heavy truck. There are several reasons for this:
Air brakes are much stronger than hydraulic brakes. This is because they use compressed air to push against the brake pads, rather than hydraulic fluid. Therefore, they can generate a much greater force, which is necessary for slowing down or stopping a large, heavy truck.
Air brakes are also more reliable than hydraulic brakes. This is because they have fewer moving parts and are less likely to leak or fail. Additionally, if one air brake chamber fails, the other chambers will still work, whereas if one hydraulic brake chamber fails, the entire system will fail.
Finally, air brakes are easier to maintain than hydraulic brakes. This is because they have fewer moving parts and require less frequent servicing.