The pedal carriage on the Penryn railway had a brake that was a semi-circular metal band that was forced onto the wheel by a lever. The ratio on the lever looks to be about 10:1. Suppose a burly quarry worker could lift 30kg with one hand. That would be a 300N force. The brake would be applied by 3000N. Eight 100kg workers in a heavy car would be at least 1 1/2 tonne. That would mean acceleration of a = F/m = 3000/1500 = 2 m/s/s. That's a fast decrease in speed so is probably unrealistic. The brake is semi-circular to give a large surface area to increase the friction since friction is a contact force.
