The edge breaks before the middle does
A slab is stronger in the middle than anywhere else, because concrete in the middle has support all the way around it. Out at the edge there is support on fewer sides and nothing at all beyond the form line, so a wheel load near the edge bends the slab in a way the same load in the middle never would.
That is why the cracking after a delivery day shows up in a predictable place. Along the outside wheel track. At the corner where the drive meets the street. Across the apron. Not down the centre, which is the part everyone watches.
Turning makes it worse than driving does. A loaded truck rolling straight puts its weight down and picks it up again. A loaded truck turning grinds and twists at the same time, and it does that with the steering axle riding wherever the driver has room, which on a residential drive is usually right out at the edge.
What is underneath does most of the deciding
The slab is only half the structure. Compacted crusher run under it spreads a wheel load out across a wide patch of ground, so no one spot has to carry much. Clay does not do that, particularly wet clay, and the native ground in this county is red clay that holds water and moves with the season.
So the same four inch driveway can be two different driveways. Poured on a base that got the stone and the compaction it needed, it usually shrugs off a delivery. Poured straight onto graded clay after a wet week, which is exactly the corner cut that makes a cheap bid cheap, the subgrade under it is soft and a loaded truck finds that out on your behalf. Which of the two you have is often not visible from the surface, and our page on what drives concrete prices covers why that shortcut happens.
Thickness is the other half of it, and it is a smaller factor than most people assume. Going thinner hurts, and a drive sold as four inches that went in at three and a half is meaningfully weaker, but a thin slab on a good base still outperforms a thick one on nothing.
A drive that is already cracked is the one to worry about
Existing cracks change the arithmetic completely, because a cracked slab is not one slab. It is several smaller pieces, each with more free edges than the whole one had, and free edges are where the weight does damage.
Walk it before you decide. Look for cracks with a lip, where one side sits higher than the other, because that is a settlement crack and it means the support under one side has already gone somewhere. Look for panels that rock slightly when you step from one to the next. Tap around with a hammer handle and listen for anything that sounds hollow.
Any of those and the honest answer is that a loaded truck will probably finish what the last ten winters started. That is not a reason to cancel your pour. It is a reason to keep the weight off and place the concrete another way.
The choice on pour day: let it up the drive, or keep it at the road
This is a real fork and both branches are legitimate. Plenty of drives take mixer trucks every day of the week without a mark on them.
Letting the truck come up is reasonable when the drive is sound, the base under it is known to be good, the ground is dry and the geometry lets a driver back straight in and pull straight out. Then you keep it to one truck at a time, keep the wheels off the outer foot of the slab, and nobody turns under load. Done that way it is a small risk taken deliberately.
Keeping the truck at the road is the other branch, and it is what we do on most drives worth protecting. The mixer stays on the pavement, our trailer mounted line pump sets up on solid ground beside it, and the concrete travels up the drive and around the house on 2.5 inch and 3 inch hose instead. A trailer pump is a small machine and it does not have to be anywhere near the forms, only near the truck. Hose lies on top of a slab rather than pressing into it, so the drive carries nothing heavier than two people and a length of line.
A gravel drive is a related question with a different answer, since the failure there is rutting and getting stuck rather than cracking, and there is a separate answer on this site for that one.
Decide it out loud before the truck is halfway up
The worst version of this conversation is the one that happens with a loaded mixer already easing up the drive and everybody looking at each other. Have it on the phone instead, days ahead, when there is nothing on the clock.
Be plain about what you want. If you would rather no loaded truck touched the driveway at all, say that when you book and the whole day gets planned around it, including where the trailer sits and which way the hose runs. If you are content for the truck to come up, say that too, because it is your drive and it is a decision you are entitled to make.
One thing that is not a judgement call. A slab poured in the last month is not ready for a loaded truck under any circumstances, and how long new concrete needs before it takes heavy weight has its own answer on this site. Do not let anyone talk you past that one on a schedule.