Why You Can’t Reverse a Route
A question that comes up again and again in our GPS Discussion Forums is Why can’t you reverse a route? A similar question with virtually the same answer is Why does my GPS pick a different route when going back to the original starting point? People often notice that a GPS might pick a different route from point B to point A than it does from A to B. Why is this? There are a few reasons.
The simplest answer is that it is simply a different route. When the GPS calculates a route and computes directions it is doing so only in one direction. So when you get to point B and want to get back to point A it needs to generate a new set of directions. But why does it sometimes take a different route? Here are a few reasons.
One Way Roads
If your original route contains one way streets then it obviously can’t go the same way for the return trip.
Keep in mind too that many Interstate Highways and Freeways are also “one way” streets and thus new directions need to be calculated. Another factor is that with a typical “clover” style exit traveling from the West and headed North you will travel further than you would going the opposite direction coming South and exiting to the West. That extra distance could cause a different route to be more efficient.
Many intersections have turn restrictions where a left turn might not be allowed, but a right turn is permitted. Thus this could cause a different route to be more efficient.
In North America a left turn often takes longer than a right turn because you need to cross more lanes of traffic. On a four lane road when turning left you need to fully cross two lanes and merge into a third lane. While turning right there are no lanes to cross and only a merge into the lane furthest right. So some GPS devices might account for this and take a route that slightly favors a right turn.
Time of Day
Newer GPS devices on the market today build routes based on time of day and predicted (rather than live) traffic. So if you go from A to B during a slow time of day but go back to point A during rush hour the GPS might pick an entirely different route based on predicted traffic patterns.
So each of these factors, and possibly others, account for why a GPS might not take the same way back to the starting point as it did going to your original destination.