Ontario · Reference · O. Reg. 668
Every rule your insurer uses to decide who was at fault, in plain English, with the split and a diagram. Link directly to any rule to cite it.
This is a plain-English restatement of R.R.O. 1990, Regulation 668 (Fault Determination Rules) under Ontario’s Insurance Act, last amended by O. Reg. 445/18. Every rule number and fault split here has been checked against the regulation. The wording is ours; the official text governs and is published free on Ontario’s e-Laws site.
This is general information, not legal advice. If a determination matters to you, raise the rule number with your adjuster or speak to a lawyer or paralegal.
Rules 1–5 are the framework. Rules 6–20 are the collision scenarios.
The centre line is whatever line is painted down the middle — single, double, solid or broken. If there is no painted line, it is the middle of the usable roadway, ignoring the parts blocked by parked cars, a snowbank or anything else obstructing traffic.
Your insurer is required to assess your degree of fault using this regulation. The diagrams published with it are illustrations only — they do not add to or limit what the written rules say.
Fault is decided without reference to the circumstances of the incident — weather, road conditions, visibility, or what pedestrians did — and without reference to where on your vehicle the contact happened. This is the rule people find hardest to accept: “it was icy” and “they hit me on the side” do not change the determination.
If more than one rule fits, the one assigning you the least fault is treated as the only rule that applies. The exception: in a two-vehicle incident, if one rule makes you 100% at fault and another makes you 0%, you are deemed 50% at fault.
If the incident is not described anywhere in the regulation, or there is not enough information to apply a rule, fault is determined under the ordinary rules of law instead.
This section covers a vehicle (A) being struck from behind by another (B) when both are travelling the same direction in the same lane.
If the front vehicle was stopped or moving forward normally, the front driver is not at fault and the rear driver is entirely at fault.
If the front vehicle was turning right or left to enter a side road, private road or driveway, the front driver is still not at fault. The rear driver carries all of it.
If the front vehicle was moving forward into a parking place on either side of the road, the front driver is not at fault and the rear driver is fully at fault.
This section covers a collision where one vehicle (B) is entering the road from a parking place, private road or driveway.
If B was leaving a parking place while A was passing it, B is entirely at fault.
If B was entering the road from a private road or driveway with no traffic signals or signs present, and A was passing, B is entirely at fault.
On a controlled-access road, if B is entering from an entrance lane and collides with A already on the road, B is entirely at fault.
This section covers three or more vehicles travelling the same direction in the same lane — a chain reaction.
Every collision between two vehicles in the chain is assessed on its own, without reference to the other impacts. This is why one driver can be not at fault for the car in front and fully at fault for the car behind.
With A leading, B second and C third and all in motion: between A and B, A is not at fault and B is 50% at fault. Between B and C, B is not at fault and C is entirely at fault.
If only C is in motion: neither A nor B is at fault for the A–B collision, and for the B–C collision B is not at fault while C is entirely at fault.
This section covers two vehicles travelling the same direction in adjacent lanes.
If neither vehicle changed lanes and both were on or over the centre line when they sideswiped, each driver is 50% at fault.
If it cannot be determined where each vehicle was on the road when the sideswipe happened, each driver is 50% at fault.
If the collision happened while B was changing lanes, B is entirely at fault.
If A was turning left at an intersection and B was overtaking to pass, A is 25% at fault and B is 75% at fault. This is one of only two places the regulation uses a 25/75 split.
If A was turning left into a private road or driveway and B was overtaking to pass, each driver is 50% at fault.
If A was turning left into a private road or driveway and B was passing one or more vehicles stopped behind A, B is entirely at fault.
This section covers three or more vehicles travelling the same direction in adjacent lanes — a pile-up.
For each collision between two vehicles in the pile-up, each driver is 50% at fault.
This section covers two vehicles travelling in opposite directions in adjacent lanes.
If neither changed lanes and both were on or over the centre line at the moment of the sideswipe, each driver is 50% at fault.
If the positions of the two vehicles cannot be determined, each driver is 50% at fault.
If B was over the centre line when the collision happened, B is entirely at fault.
If B turned left into A’s path, B is entirely at fault. This is the classic left-turn collision.
If B was leaving a parking place or entering from a private road or driveway while A was overtaking another vehicle, B is entirely at fault.
This section covers intersections with no traffic signals and no traffic signs.
If A entered the intersection before B, B is entirely at fault.
If both entered at the same time and A was to the right of B, B is entirely at fault. The vehicle on the right has the right of way.
If it cannot be established which vehicle entered first, each driver is deemed 50% at fault.
This section covers intersections controlled by traffic signs rather than signals.
If B failed to obey a stop sign, yield sign, similar sign, or flares or signals on the ground, B is entirely at fault.
If both failed to obey a stop sign, each driver is 50% at fault.
If it cannot be established who failed to obey the stop sign, each driver is deemed 50% at fault.
At an all-way stop, if A arrived first and stopped, B is entirely at fault.
At an all-way stop, if both arrived and stopped at the same time and A was to the right of B, B is entirely at fault.
If it cannot be established who reached the all-way stop first, each driver is deemed 50% at fault.
This section covers intersections controlled by traffic lights.
If B failed to obey a traffic signal, B is entirely at fault.
If it cannot be established whether either driver disobeyed the signal, each driver is deemed 50% at fault.
If the traffic signals were inoperative, fault is determined as though the intersection were an all-way stop.
This section covers incidents in parking lots.
A collision on a parking lot thoroughfare — a main route into, through or out of the lot — is assessed using the rest of this regulation as though the thoroughfare were a road.
If A leaves a feeder lane and fails to yield to B on a thoroughfare, A is entirely at fault. A feeder lane is any parking lot road that is not a thoroughfare.
If A leaves a parking space and fails to yield to B on a feeder lane or thoroughfare, A is entirely at fault.
If A is parked when struck by B, A is not at fault and B is entirely at fault.
If A was illegally parked, stopped or standing when struck, and the incident happened outside a city, town or village, A is entirely at fault and B is not. Note the geographic limit — this reversal does not apply within a municipality.
A driver is entirely at fault if the collision happens while they fail to obey a police officer’s direction, a do-not-enter sign, a prohibited passing sign or a prohibited turn sign.
A driver is entirely at fault for a collision that happens while backing up, while making a U-turn, or when the driver or a passenger opens a door or leaves one open. This last one covers dooring a cyclist or a passing vehicle.
For this regulation a driver is considered charged with a driving offence if, as a result of the incident, they are charged with impaired operation by alcohol or a drug, driving over the legal blood alcohol limit, an indictable offence related to operating the vehicle, failing or refusing to provide a breath sample, or exceeding the speed limit by 16 km/h or more.
If the driver of A is charged with one of those offences and the driver of B is wholly or partly at fault under these rules, fault is determined under the ordinary rules of law instead of this regulation.
Your insurer matches the facts of your collision to a scenario in this regulation and assigns the resulting percentage. It is a matching exercise, not a judgement call, which is why two adjusters should reach the same answer on the same facts.
Fault is recorded in your claims history and, at 25% or more, can affect your premium. Some insurers rate from 25%; the Financial Services Regulatory Authority treats 50% or more as chargeable. If you disagree, ask which rule number was applied — that turns a vague disagreement into a checkable one.
The full route is in how to dispute a fault determination.
The fault calculator takes a description of what happened and matches it to a scenario, then estimates what the resulting fault percentage does to your renewal.
The authoritative version is R.R.O. 1990, Regulation 668 under the Insurance Act, published on Ontario's e-Laws website. This page sets out every rule in plain English with the rule number and the fault split so you can find and cite the one that applies, but the official wording governs. The regulation was last amended by O. Reg. 445/18, effective October 2018.
Yes, that is what this page is for. Every rule and subsection has its own permanent anchor, and the 'Link to this rule' button copies a URL that opens the page scrolled to that exact rule with it highlighted. That makes it straightforward to reference a specific rule in a forum reply, a letter to an adjuster or an article.
No, and this is the provision people find hardest to accept. Rule 3 states that the degree of fault is determined without reference to the circumstances in which the incident occurred, including weather conditions, road conditions, visibility or the actions of pedestrians, and without reference to where on your vehicle the contact happened. Ice, fog and a blind corner do not change the rule that applies.
Rule 4 handles this. Where more than one rule applies, the rule that attributes the least degree of fault to you is treated as the only rule that applies. There is one exception: in a two-vehicle incident, if one rule would make you entirely at fault and another would make you not at fault, you are deemed 50 per cent at fault.
Rule 5 covers it. If the incident is not described anywhere in the regulation, the degree of fault is determined in accordance with the ordinary rules of law. The same applies where there is insufficient information about the incident to apply a rule. In practice this is why unusual collisions take longer to resolve.