The intersection rule

Bruce Nevin offered a rule of thumb for drivers.

It takes about as long for the car in front of you to start moving as it does for the traffic coming the other way to reach you.

The key point here is that disturbances in traffic propagate and you will be able to better ‘go with the flow’ if you anticipate when starting or stopping traffic is going to impact you. You do this by keeping eye on the horizon to detect when a disturbance starts and then estimating when it will impact traffic near you.

Another rule is to keep a 2 second difference between you and the vehicle ahead. For RV’s it might be better to try for 3 or 4 seconds. At 50 mph, that would be about 200 to 300 feet (10 to 15 typical car lengths).

Note: You can do a Google search for 50 mph infeet per second to find out that 50 mph is about 73 feet per second as Google will interpret the query as a request for a calculation. You’ll get an answer plus a number of other interesting related links to peruse.

Using a time delay for vehicle separation is a lot more reliable than trying to use car lengths or such guides. Just note when the bumper of the vehicle in front passes a paint stripe or road marker and then do a slow count – one thousand and one, one thousand and two – to calibrate your eyeball distance estimate.

You need to anticipate disturbances in traffic so you can make adjustments easily and smoothly rather than as an emergency maneuver. It provides time for those behind you to see that something is happening so they too can take action to avoid problems like running into you.

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