How Far Can You See When Driving at Night?
Freeways in British Columbia are governed by posted speed limits of up to 120 km/h and for the most part are only lit by a driver's headlights at night. The opposing lanes are fairly close together and require the use of low beam headlamps when other traffic approaches. When the highway is busy drivers are often forced to travel long distances on low beam. How safe is this at 120 km/h?
The average vehicle takes about 81 meters to slide to a wheels locked panic stop at 120 km/h. Some may stop a bit faster and more than a few will take longer, particularly pickup trucks and other larger vehicles. A driver who is alert and expecting problems will likely have about one second pass between identifying something on the road and actually getting the brakes applied. This means a further 33 meters of travel, bringing our total stopping distance to 114 meters.
Transport Canada says that the low beam lighting system of most vehicles allows a driver to see about 140 meters. It may seem further, but after that point most of the light is on the shoulder and the right ditch rather than on the lane ahead. This applies to both halogen headlights and the new gaseous discharge lamps.
The 26 meter distance between the end of the stopping distance and the end of the sight distance is travelled in less than a second. This is not a lot of time for a driver to react if they are not looking at the part of the roadway the obstruction is in, or are not completely alert and expecting to take action.
The gist of the calculation is that 120 km/h may not be a good night speed for drivers.