Braking distance is a factor of speed, weight, brakes, tires and road surface. A 40 ton truck can only stop so fast with rubber tires on typical brakes on a typical highway road surface.
Race cars are designed to stop faster than passenger cars. Their brakes are huge, they're designed with exotic components to transfer heat to air faster, designed to take higher heat for longer, the cars are designed to flow air over the brakes, and they cost much more and don't last as long, and have advanced computerized systems to optimize brake utilization. They also have pretty big tires (usually for power transfer, not braking). Their tires are also grippier on a given surface at a higher tire temperature, so they cost more and don't last as long, and work best on dry flat surfaces. They strip all the weight out of the car to decrease the amount of force working against the tires and brakes. Even the suspension and shell is designed to increase tire, and thus brake, traction. They stop really goddamn fast - 93 feet for a Ferrari F430 Scuderia, from 60mph.
Trucks are designed to carry 40 tons up and down hills, survive tire blow-outs, brake system failures, and more miles than 1000 F430s will ever see, on all kinds of road surfaces and temperatures. It is possible to improve the brake time, but it would probably cost so much you might as well ship your produce in a Ferrari. Halve the weight they carry to reduce braking distance and now we have to have twice the trucks to carry the same loads, but you still have a vehicle 10x heavier than other vehicles with dynamics that simply can't move around like the lighter ones. More accidents would be guaranteed.