Can you tar and chip over an existing driveway?
Short answer: often yes. Tar and chip is a surface dressing, so if your existing driveway is structurally sound it can usually be laid straight over the top. That's exactly what makes it such good value for resurfacing a tired drive.
When it works
If your current tarmac or concrete is solid, level and free of major cracks or potholes, it makes an ideal base. The bitumen bonds to it and the chippings lock in, giving a fresh finish without the cost of digging everything out.
When it doesn't
If the existing surface is crumbling, badly cracked, sinking, or sitting on a failed base, laying over the top just hides the problem, and it comes back. A good installer will tell you honestly whether yours needs repair or a new sub-base first.
The honest rule
Resurfacing saves money only when the foundation is sound. Anyone who offers to "spray over" a failing drive without looking underneath is exactly the sort to avoid. See how to choose a good installer.
Not sure what shape your base is in? Get a free assessment.