[1123581321]

If they are replacing bifocals, the wearer needs both a near- and far-sighted prescription. Far-sighted only would never need these.

Either failure mode would be dangerous while driving because you need to be able to read your dash.

[cout]

I don't need to be able to read my dash. I only need to see where the needle is pointing.

[WalterBright]

It's not a crisis if you cannot read your dash. How often do you look at the oil pressure gauge, for example? As for speed, just move with the traffic.

[bluGill]

I had a car with a broken dash. The only thing I missed for the month until I fixed it was the fuel gauge. I probably didn't estimate my speed very accurately but I was close enough to not get a ticket.

[WalterBright]

Yes, with my old cars I've had broken dashes, too. I discovered I maintained speed by the engine pitch - because when I drove a silent car, I couldn't seem to maintain a consistent speed!

As for the gas gauge, the trick is to reset the local odometer at every fillup, and you'll have an indication of the remaining fuel. Some older cars don't even have a fuel gauge, they just have a lamp that glows when it gets low.

[bluGill]

I my case I tore the dash apart because the speedometer wasn't working, and the odometer is connected to that. Only after tearing the dash apart could I see the cable to the transmission wasn't turning. Until I found the real problem there wasn't a hurry as I removed the cable several times before I found what was really broke.

[WalterBright]

On my car the needle fell off the speedo!

[1123581321]

Yes, it is a problem. There should be no controversy about saying that clear vision reduces distractions and confusion when operating something.

If you want to talk specifics, you’re supposed to be able to see your speed and how your car is performing. You should be prepared for contingencies, like your temperature changing or a yellow/red warning on the dash. You may need to deal with a problem in the car, like grabbing something that could slide under the pedals.

The same goes for farsighted driving. Yes, in most cases you could just follow traffic and you wouldn’t need to read street signs or look at traffic a mile ahead. But you need to be prepared for unexpected situations, and you’ll generally do worse just mentally managing your reduced vision.

I’ve driven without my glasses and tested an unexpectedly bad trial prescription in a car, if it matters.