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.

> 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.

A lot of that isn't to brake faster but to keep the brakes from overheating from constant high use during a race that can last a couple hours or more. For normal emergency use you can drop a lot of that because they only need to be used extremely hard rarely and they'll have time to cool.

In other words, look at aircraft, not at racecars. What you have described is practically the only mode of operation for wheelbrakes there ("brakes catch fire during emergency braking? No biggie, just keep an eye on them while they cool.").

Brake heating is not a real issue with emergency braking, only with frequent braking which race cars do. That's why "upgrading" to "big brake" systems on passenger cars is usually a waste of money and reduces performance: unless you're driving on a track where you have to brake a lot, and the cumulative braking keeps the brakes hot, you're not helping. Even worse, the brake pad compounds used for race cars are different, and are designed to maintain performance even when very hot, whereas passenger car brakes have to have great performance when cold.

The bottom line is: a single panic stop on the highway isn't limited by your brakes on a passenger car, it's limited by your tires. The more friction your tires have with the road, the faster you'll slow down.

So yes, if you want a 40 ton truck to stop faster, it's completely doable: just increase the amount of rubber in contact with the road. Adding more wheels will do that quickly. However, more tires means more rolling friction which means less fuel economy and fuel economy is critically important to long-haul trucking. Also, adding more axles causes maneuverability problems in the city. Notice that on standard trailers, the rear axle set can be moved forward and back. They set them in the rearward position for long hauls, and in the forward position for shorter hauls.

If there's no driver in the equation (no monthly salary to pay), I guess the the incentive will shift towards having more, smaller trucks.

Not necessarily. More, smaller trucks will mean your transport costs will go up because you get less economy of scale. Eliminating the driver helps mitigate that of course, but going to smaller trucks then eliminates the savings you got by eliminating the driver. Having more, smaller trucks would be more versatile however, if you don't need to transport full truckloads of cargo between certain points.

Also, drivers as I understand it aren't paid monthly salaries, they're paid by the mile.