Considering the Meaning of the "Horizontal Line" on Supplementary Signs

Supplementary signs installed below main traffic signs play the role of providing detailed information on the application conditions or content of the main sign, conveying additional information to drivers. However, there are some matters among them that are not taught in detail at driving schools. One of these is the "horizontal line" drawn within supplementary signs. This article focuses on the meaning of this horizontal line.

Does the presence or absence of a horizontal line affect the meaning of a supplementary sign?

The horizontal line on a supplementary sign is called a "division line", and it is explained in the Traffic Regulation Standards issued by the National Police Agency. At first glance, it looks like a meaningless design, but the rules for when a division line is drawn are stipulated as follows.

In other words, when attaching two or more conditions to a supplementary sign, normally the supplementary signs would be lined up separately for each condition, but when combining them into one board, a black division line is drawn between the two conditions.

Here, let's pay attention to the phrasing "may be provided" for the division line. This means that (in many cases) it is optional to provide it or not. In fact, even for supplementary signs with the same meaning, the presence or absence of a division line differs depending on the prefecture.

Note that if two conditions of the same type (for example, two time periods) are lined up vertically, no horizontal line is provided.

Classification of Supplementary Sign Content and Horizontal Lines

By the way, what does it mean when two or more supplementary signs are installed on a main sign? Let's think about this.

To consider the meaning, let's first look at the list of "types of supplementary signs." The types are as follows, and they are supposed to be displayed in this order from top to bottom.

Here, since ❹ only states the reason, it does not affect the content of the regulation. Therefore, it can be seen that there are three independent axes for the regulation content: ❶ to ❸ (❶, ❷, and ❸ can each be specified independently). Also, regarding ❷, there are further independent axes for ① to ③ (①, ②, and ③ can each be specified independently).

Depending on the prefecture, a division line may or may not be inserted between ❶, ❷, ❸, and ❹. The same applies between ①, ②, and ③. However, the meaning does not change whether there is a division line or not.

Interpretation using logical expressions for multiple recorded contents

By the way, the information recorded on supplementary signs is sometimes written in Japanese that is quite difficult to understand. Let's try to interpret the content of supplementary signs using "logical expressions" (NOT / AND / OR / XOR operators) that you might have learned when studying high school mathematics or computer science.

The simplest example is the interpunct "・" (or the comma "、").

When multiple conditions of the same type are connected by interpuncts in a single line, the interpunct corresponds to an "OR" operator (logical disjunction) .

Next is the case shown below, where a "negative form" is used within a single line. These all represent a "NOT (XX)" (logical negation operator) .

Also, while it may span two lines, there are cases where two different types of conditions are connected by particles, such as "XX is ✖✖" or "XX's ✖✖".

In these cases, it becomes an "AND" operator (logical conjunction).

Based on this, let's interpret the conditions under which the following "Pedestrian Only (Specific Prohibited Area)" is implemented using a logical expression. In this example, three conditions—day of the week, month, and time—are intertwined with the inclusion of particles like "no" and "wa".

The conditions shown in this example are as follows.

It's quite difficult to decipher 💦

Conditions on different axes are usually connected by an "AND" operator

Regarding the types of supplementary signs ❶, ❷, ❸, and the classifications ①, ②, ③ within ❷, when they are displayed vertically within the same supplementary sign in numerical order (order of display priority), they are connected by an "AND" operator.

This is easy to understand if you imagine a 3D space where ❶, ❷, and ❸ are each an axis. Since each condition is independent, the rectangle (or rectangular parallelepiped) cut out by the conditions on each axis using AND represents the conditions indicated by the entire supplementary sign.

Let's interpret the conditions under which the following "Time-Restricted Parking Zone" is implemented using a logical expression. The conditions separated by horizontal lines are, from top to bottom, the ❷-① condition, the ❷-② condition, and the ❸ condition.

The correct interpretation is as follows.

A horizontal line is often inserted when using the 'OR' operator for compound conditions.

For main signs such as 'No Vehicles,' 'Pedestrians Only,' 'No Entry Except Specified Direction,' 'No Parking,' and 'No Stopping or Parking,' there are cases where content that should originally be divided into two pairs of main and supplementary signs is combined into one pair. In this case, there is a high probability that a horizontal line will be inserted between the contents of the two supplementary signs.

The following is an example of this.

Looking at the supplementary sign, both above and below the horizontal line, 'Vehicle Type' and 'Time' are listed. Since both the top and bottom are the same compound conditions, the meaning of this horizontal line is the 'OR' operator.

If the display priority of the conditions above and below the horizontal line is the same, or if the display priority is reversed across the horizontal line, the meaning of the horizontal line is the 'OR' operator.

The conditions shown in this example are as follows.

Here, the unfamiliar 'XOR' operator (exclusive OR) appears, but this can be expressed as 'XX XOR YY' when written as 'XX (excluding YY)' and the set YY is completely contained within the set XX.

In this way, a sign with a horizontal line represented by an 'OR' operator in the supplementary sign can be broken down into two regulations. Incidentally, the condition 'vehicles other than large vehicles, etc.' has the same meaning even if it is not attached, because the same regulation is included in the 'large vehicles, etc.' side for a longer period of time. (Depending on the prefectural public safety commission, it is intentionally attached because they want to display the conditions so that the ranges of the two similar regulatory signs do not overlap.)

Interpretation with concrete examples

Now, let's look at actual concrete examples and express the content of the supplementary signs in logical formulas. There are often cases where highly difficult and complex supplementary signs are installed for No Parking, No Entry Except Specified Direction, No Vehicles, No Entry, and Pedestrians Only.

No Parking

First, let's look at a case where two supplementary signs are installed: one with three conditions displayed and another one.

Since two different conditions ❷-③ regarding time are set side by side, the correct answer is to connect them with an 'OR' operator. Since two ❸s are also lined up, the space between them is also an 'OR' operator.

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How about the following example? Although this spans multiple lines, the conditional statement itself is one.

Since the particle 'no' was to be connected with an AND operator, the correct answer is

is the result.
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How about the next one?

“Within the parking method marking lines” is a specification of a location meaning “it is the rule to park inside the marking lines,” and it is connected to “start of section” with an “AND” operator. Therefore,

is the correct answer.
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How about the next example?

In this case, considering the order, the display priority is reversed between the first right arrow (start of section) and the second block (complex condition of time and vehicle type), so the horizontal line between them is considered an “OR” operator.

It is easy to understand if you think of the first “start of section” and what follows as being on two separate signs.

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How about the next example?

What is different from before is that in addition to the auxiliary signs, there is also a time regulation at the top of the main sign. The time regulation at the top of the main sign is interpreted by inserting it into the prescribed display priority position of the auxiliary signs.

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How about the next example?

In addition to the time regulation at the top of the main sign, there are conditions for vehicle type, day of the week, and section. You can interpret it if you organize it calmly.

No entry for vehicles except specified direction, no vehicles, no entry for vehicles

How about the following example?

This is a supplementary sign with conditions spanning 7 lines, which is quite complex. A single 'horizontal line' is drawn, and this plays the role of an 'OR' operator. There is a 'No vehicles' regulation on the right-turn side, and the same supplementary sign is installed. The upper half indicates that 'light vehicles other than bicycles' are regulated all day, and it is famous for having a so-called 'No handcart entry' sign installed as a variable sign.

The interpretation is as follows.

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How about the following example?

This is a very vertically elongated supplementary sign spanning 6 lines. In the case of Kanagawa Prefecture, reduced-size supplementary signs have a particularly vertically elongated layout.

Setting that aside, regarding the interpretation, based on the fact that vehicle types and 'day of the week + time' sets are arranged in parallel, it becomes as follows.

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How about the following example?

Combinations of 'No entry for vehicles except specified direction' with 'Excluding bicycles', 'One-way traffic', and 'arrows' can be seen in Tokyo and several other prefectures. 'One-way traffic' and 'arrows' both indicate the reason for the regulation and are a set. No horizontal line is inserted between them.

On the other hand, what is special about this example is that '0-12' is placed below the reason for the regulation. This road is a reversible one-way street, but in other locations with reversible one-way streets, the time display is in the middle, so this is likely a display error at this location.

The regulation content can be interpreted as follows.

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How about the following example?

Because the auxiliary signs are split into two, it might look like they consist of two separate regulations: one where small special vehicles and light vehicles can only go straight, and another where small special vehicles and light vehicles can only go straight from 7-8 and 15-17, excluding Saturdays, Sundays, and holidays, while others can also turn left or right.

To conclude, this is a single regulation, and the two split auxiliary signs represent one regulation. Looking at the left side, since the following regulation (School Zone, pedestrian/light vehicle only during mornings and evenings on school days) is applied, it is clear that the regulation is one.

In this case, it seems the auxiliary sign was split into two because it became too vertically long to fit. It's confusing 💦

Depending on the prefecture and the era of installation, there are cases where conditions for different axes are expressed in one line, or grouped together in parentheses as 'excluding ~'.

Pedestrians only

How about the next example?

It is a vertically long auxiliary sign spanning seven lines. A 'horizontal line' is drawn, with time conditions listed above and a combination of day and time conditions listed below. Since both are time-based conditions, it is reasonable to interpret this horizontal line as an 'OR' operator. In other words, this sign summarizes two different pedestrian-only regulations.

The first regulation is for pedestrian-only access from 15:00 every day until 5:00 the next day. Unusually for a busy district in Tokyo, there is no 'excluding bicycles' clause. This means bicycles are also prohibited during these hours. However, please note that vehicles exempt from the regulation, such as designated vehicles and permitted vehicles, may still enter during these hours.

The second regulation concerns the 'pedestrian paradise' held on Sunday and holiday afternoons. Since this is a 'specific prohibited area', vehicles including bicycles, light vehicles, and even designated or permitted vehicles are prohibited from passing.

The content of the auxiliary sign can be interpreted as follows.

Represented on a timeline, it looks like this.

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How about the next example?

In this example, time-based displays appear on the 2nd, 3rd, and 4th lines. While the 2nd line shows only time, the 3rd-4th lines show days and times, which feels unbalanced. However, since the expression 'every day of the year' does not exist in auxiliary sign terminology, it is written this way.

The interpretation is as follows.

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How about the following example?

This one is longer and more complex than the previous example, but since the "day of the week + time" sets are parallel, it can be interpreted more naturally than the previous example in that sense. Note that looking at this regulation, no pedestrian-only regulation applies on Saturdays.

The interpretation is as follows.

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How about the following example?

This is a very complex example where the supplementary sign has an explanation spanning 9 lines, divided into 4 areas by 3 horizontal lines. However, if you analyze it calmly based on the practice so far, you can understand it.

Of the three horizontal lines, the top one separates "vehicle type" and "day/time," so it acts as an "AND" operator. The second horizontal line acts as an "OR" operator because the content separated above and below is of the same type. Note that while the final fourth area is not parallel, the third horizontal line is also an "OR" operator, and the fourth area is parallel to the second and third areas.

The second and third areas consist of ❷-① day of the week and ❷-③ time (the second area also has "time" in parallel), but the fourth area has ❷-② date added before the ❷-① day of the week and ❷-③ time. To make these parallel, it is necessary to assume that there is an omitted ❷-② date before the second and third areas.

Since the ❷-② date for the fourth area is "4th, 14th, 24th," what is implicitly attached to the second and third areas is "every day of the year." Alternatively, since the regulated time zone for specific days in the fourth area is broader than the regulations in the second and third areas, it is also acceptable to include "except 4th, 14th, 24th." (Tokyo often does not use a method where conditions are set to avoid overlapping. In Kanagawa Prefecture, etc., they are set to avoid overlapping, so "except 4th, 14th, 24th" is included.)

Based on this, the interpretation is as follows.

Summary

How was it? You have to decide in an instant whether to connect different regulatory conditions with an "AND" operator or an "OR" operator, which I think is quite difficult.

In summary, the horizontal line (black dividing line) itself has no meaning; its purpose is simply to provide a division to make things easier to understand, and there is no difference in meaning whether the horizontal line is present or not. However, when different types of conditions are lined up vertically in the order of "vehicle type," "day/time," and "section/area/location," it is an "AND" operator, and when conditions of the same type are lined up vertically or the order of the above conditions is reversed, it is an "OR" operator—you need to keep this in mind to construct and interpret the logical expression.