In most traffic situations, there is at least one line of traffic in each direction permitted. Therefore, drivers are unprepared when they encounter single-line situations -- there is room for only one line of traffic to pass on a two-way road. What you do depends on which of the following three conditions you encounter:

  1. Supervised control of single-line traffic
  2. One short single-line section (neck-down, or single stopped vehicle)
  3. Long or multiple single-line sections (excessive parking or one-lane bridge)

single-line diagrams The key requirement in single-line driving is to not be greedy. Whenever a greedy driver enters a single-line section before it is his turn, he delays not only himself, but all other vehicles on the road, by creating a blockage. It can take a quarter of an hour or more to clear up a single-line blockage, especially if a driver who does not understand single-line driving is present. When in doubt, yield.

Here are the various methods to use when faced with a single-line situation in traffic. Some of them have been resurrected from the horse-and-buggy days, when single-line roadways were more common. Each case is different, so each case has a different set of rules:


    Supervised control is the easiest form of single-line traffic for the motorist to drive through, because traffic control devices are in place. Traffic lights, flagmen, workers with paddles, or pilot vehicles, determine when traffic is permitted to enter the single-line section. The timing of the releases of traffic are determined by the length and number of single line sections, the amount of traffic on the road, and the length of any passing loops between single-line sections. The driver needs to do nothing but obey the traffic controls present. This is the only single-line method that allows cars to group into platoons. It is usually used in construction zones or at one-lane bridges.

    There is one case that needs to be clarified under supervised control. If a driveway exits into the single-line section, and no flagman or signal is present at the driveway, then the driver must follow these rules:


    The main idea here is to alternate traffic direction car-by-car. Here are the rules:


    Here is absolutely essential that only one vehicle is in this kind of single-line section at any time. Failure to obey these rules will lock up the section, or a passing loop, with vehicles intending to go in both directions blocking each other's paths:

The SAW-BY* maneuver

The saw-by* is a maneuver which is used to avoid a blockage in a single-line passing loop. It is much better to avoid locking up a passing loop than using a time-consuming double-saw* to unlock it. The saw-by is simple to perform:

  1. Any vehicles waiting to proceed in the opposite direction must wait in their passing loops until the offending vehicles have passed.
  2. If any driver gets greedy and does not wait in the passing loop until the offending vehicles have passed, a double-saw will be needed.

single-line diagrams The DOUBLE-SAW* maneuver

The double-saw is a maneuver to be avoided, unless a passing loop locks up. It is much better to avoid locking up a passing loop, but if it happens, the double-saw is the only way to unlock it.

  1. If any cars can alleviate the situation by temporarily turning into driveways, they must do so.
  2. The shorter line of cars occupying a single-line section must back up enough for the longer line to pass forward enough to free the exit of the passing loop. If some of them enter another passing loop in the process, those cars must stay there until the blockage clears, unless the passing loop is too short to hold all of them (step 1 of figure).
  3. The entire longer line must move forward until it clears the exit of the passing loop. If some of them enter another passing loop, the entire long line must proceed forward, one at a time, until the blockage clears (step 1 of figure).
  4. The cars still in the passing loop are now freed, they must leave, one at a time, until the passing loop is empty (step 1 of figure).
  5. The longer line (if it hasn't cleared) must back up until it allows more of the shorter line to enter the passing loop (step 2 of figure).
  6. As many of the cars in the shorter line that will fit in the passing loop must move forward and enter it. The remainder (if any) should stay where they are instead of moving forward (step 2 of figure).
  7. The longer line (if it still exists) must move forward again until it clears the exit of the passing loop (step 3 of figure). If nothing is blocking their way, they must proceed to the next passing loop.
  8. The cars from the short line which are now in the passing loop must proceed forward, one at a time, until the passing loop is empty (step 3 of figure).
  9. If the blockage has not cleared, repeat steps 3 through 8 until it clears out.

* These names came from the terms used by railroads for the same maneuvers.

Single-line driving is an unusual situation that can trap the unwary. Be prepared for it, so you don't get trapped.