how far ahead should drivers look while driving?
One good rule for how much space you should keep in front of you is at least 1 second for each 10 feet of vehicle length at speeds below 40 mph. At greater speeds, you must add 1 second for safety. For example, if you are driving a 40-foot vehicle, you should leave 4 seconds between you and the vehicle ahead. In a 60-foot rig, you will need 6 seconds. Over 40 mph, you would need 5 seconds for a 40-foot vehicle and 7 seconds for a 60-foot vehicle.
To help you become better at scanning for hazards, here is a good routine to develop. Look up to 12 seconds ahead. In a 60km/hour zone this means looking up to 200 metres ahead; on a freeway at 90km/hour it is up to 300 metres. The next picture shows what this looks like at 50km/hour.