Japan's Pavement Inspection Guidelines, and why potholes are left out

Japan's Pavement Inspection Guidelines (MLIT, October 2016) sort roads into classes A to D. Classes A and B are inspected at roughly once every five years or more; classes C and D follow an inspection plan the manager sets (Source: MLIT). Diagnosis has three levels: I Sound, II Surface function maintenance stage, and III Repair stage. Emergency response to sudden damage such as potholes is outside the guidelines and is handled as soon as it is found on patrols and the like.

Flowchart of the pavement maintenance cycle: inspection, diagnosis (I to III), action (minor repair or rehabilitation), then records, which lead back to the next inspection. For classes C and D, information from patrols and resident reports also feeds into diagnosis. Emergency pothole response sits outside the frame as excluded — Fig. 1 The cycle of inspection, diagnosis, action and records. For classes C and D, information from patrols and resident reports is also used in diagnosis

Key points of the guidelines

The guidelines set out the basics of pavement inspection under Article 35-2 of the Road Act Enforcement Order. Bridges and tunnels are covered by separate rules, based on close visual inspection every five years with four diagnosis levels, I to IV, so don't confuse them with pavement's three levels (Sources: Road Act Enforcement Regulations Art. 4-5-6, MLIT notice).

Item	What the guidelines say
Covers	Carriageway pavement (including on bridges and in tunnels)
Excludes	Emergency response to sudden damage such as potholes
Road classes	Four, A to D. The road manager decides which applies
Inspection frequency (A, B)	Set by the manager, roughly once every five years or more
How inspection proceeds (C, D)	The inspection plan sets how many years one full round takes
Management indicators	For A and B, basically crack ratio, rut depth and IRI (roughness). For C and D, set by the manager
Diagnosis	I Sound / II Surface function maintenance stage / III Repair stage
Records	Results of inspection, diagnosis and action are kept for as long as the pavement is in service

The table describes asphalt pavement. Concrete pavement has separate rules in Chapter 7, where level II is called the "minor repair stage".

How are classes A to D decided?

Class	Typical roads	How fast damage progresses
A	High-standard arterial highways and other roads with high service levels such as high-speed travel	Fast
B	Roads with heavy truck traffic, roads where pavement deteriorates quickly, etc.	Fast
C	Roads with light truck traffic, etc.	Gradual
D	Residential streets, etc.	Very slow

Each road manager decides the class. The guidelines note that a municipal road may be put in class B at the manager's discretion, and ask for reviews as traffic changes.

How often are inspections?

For classes A and B, the manager sets the frequency at roughly once every five years or more. A target service life, the period the surface is meant to stay in use without rehabilitation, is also set, and inspections are judged against it. The manager chooses the method, such as visual inspection or equipment.

Classes C and D have no fixed number of years; the inspection plan sets how many years one round takes. Where intervals are long, the guidelines say it is desirable to fill in with information from patrols. For class D, managing by finding damage during patrols, then acting on and recording it, is acceptable.

Roads managed by the state have their own version of the guidelines (March 2017). All state-managed national roads are class B, and the basic rule is to inspect every lane of every route once every five years (Source: MLIT).

Rough thresholds for levels I to III

Diagnosis is made against the management standard the manager has set. The guidelines' appendix gives example judgements for a standard of 40% crack ratio and 40 mm rut depth, stressing that these are only examples. For classes C and D, examples include crack ratios of 20 to 40% and rut depths of 20 to 40 mm.

A band chart with crack ratio on the horizontal axis. About 0 to 20% is I Sound, about 20 to 40% is II Surface function maintenance stage, about 40% or more is III Repair stage. The 40% mark is the management standard line — Fig. 2 Example of crack ratio and diagnosis levels with a 40% management standard

Level	Crack ratio	Rut depth
I Sound	About 0 to 20%	About 0 to 20 mm
II Surface function maintenance stage	About 20 to 40%	About 20 to 40 mm
III Repair stage	About 40% or more	About 40 mm or more

For IRI (International Roughness Index, the longitudinal unevenness of the surface), the appendix gives class A and B examples of up to about 3 mm/m for I, about 3 to 8 mm/m for II, and about 8 mm/m or more for III. In the guidelines, rehabilitation restores the original function, while minor repair keeps the current function while still below the management standard.

At level II, if the pavement looks likely to reach III before its target service life, minor repairs such as sealing cracks are carried out. For classes A and B, level III splits into III-1 (surface rehabilitation) if the surface has been in service longer than its target life, and III-2 (base course replacement, etc.) if not, since damage below the base course is suspected. III-1 is mainly milling and overlay; III-2 involves a detailed survey followed by base course replacement or similar.

Why is pothole response excluded?

The guidelines aim to make pavement last longer by rehabilitating the surface and binder courses early and protecting the layers below the base course. Dealing with sudden, safety-related damage such as potholes is a different kind of task, so the guidelines exclude it as "something to be dealt with as soon as it is found on patrols and the like".

Deciding from patrol information that cracks need sealing, and doing it, is within the guidelines, though. How holes form is explained in Why do potholes form?

How do the guidelines treat resident reports?

I am developing a service that passes residents' reports on to road managers, so I'll also be clear about the limits of reports. The guidelines mention resident reports in two places, and not in the section on asphalt pavement for classes A and B.

In the notes on diagnosis and action for classes C and D: information from patrols and from handling resident reports is also used. On roads where a full inspection round has not yet been completed, damage equivalent to level II or III may be identified from reports and acted on
In the notes on concrete pavement: if there is a report of problems at joints, it is good to check the condition visually case by case

Information the manager needs	Can reports provide it?
Location, date and appearance of damage	Yes. A lead until the inspection round comes around
Crack ratio, rut depth and IRI values	No. They are section-level indicators that one photo can't determine
Surface service years and condition below the base course	No. Registers and detailed surveys are needed

Reports skew towards busy streets, the same damage gets reported several times, and people judge severity differently. Reports are no substitute for periodic inspection; treating them as information that fills the gaps between inspections on roads with long intervals, like classes C and D, matches how the guidelines are written.

How do you check which version is current?

Check the list of inspection guidelines on MLIT's road deterioration countermeasures page (Source: MLIT). As of September 27, 2026 it lists the October 2016 version; the "March 2017" guidelines that come up in searches are the version for state-managed roads.

For road managers I am developing MICHIKARTE, a service that lets road users record damage they find with a smartphone and passes it on to road managers.

Last checked: September 27, 2026

What are Japan's Pavement Inspection Guidelines? And why pothole response is left out