There is a huge parking and picnic facility about three kilometers (2 miles) from the falls where you can safely leave your car, van, bike, etc. Called: Rapids View Parking Lot. Have a snack or a short picnic and take the shuttle bus down to the falls. The bus price is included in the parking fee.
The cost is about $4- / person. The shuttle bus leaves and arrives every 10, 15 minutes.
This is the most convenient way visiting the falls, the tower, the boat ride and see downtown as well.
On this image you see highway 401 around Toronto as we were going to Niagara. There were about ten lanes all together. Picture is taken from inside the car.

