Is Failing to Signal Illegal?
In Ontario, Failing to Signal Is a Traffic Offence With a Penalty of Two Demerit Points (Five CVOR Points For Truckers) and $110 Total Fine Including Costs and Surcharge. Interestingly, Successful Prosecution Requires Proof That Another Vehicle Was Potentially Affected.
A Helpful Guide For How to Understand the Law Regarding Proper Signaling As a Warning For Others Using the Road
When a driver forgets or fails to use a signal to advise other drivers of an intent to change lanes or make a turn, such forgetfulness or failure is both annoying as well as potentially dangerous as other drivers are without a warning and are thereby unable to anticipate what becomes a sudden lane change or turn. Equally frustrating can be the driver that uses a signal; however, the signal is applied only at the last moment in a manner that fails to warn of a forthcoming move and instead becomes simply an indicator of what the driver is doing immediately rather than properly as a proper warning of what the driver is about to do.
142 (1) The driver or operator of a vehicle upon a highway before turning to the left or right at any intersection or into a private road or driveway or from one lane for traffic to another lane for traffic or to leave the roadway shall first see that the movement can be made in safety, and if the operation of any other vehicle may be affected by the movement shall give a signal plainly visible to the driver or operator of the other vehicle of the intention to make the movement.
(2) The driver or operator of a vehicle parked or stopped on the highway before setting the vehicle in motion shall first see that the movement can be made in safety, and, if in turning the vehicle the operation of any other vehicle may be affected by the movement, shall give a signal plainly visible to the driver or operator of the other vehicle of the intention to make the movement.
(3) The signal required in subsections (1) and (2) shall be given either by means of the hand and arm in the manner herein specified or by a mechanical or electrical signal device as described in subsection (6).
(4) When the signal is given by means of the hand and arm, the driver or operator shall indicate his or her intention to turn,
(a) to the left, by extending the hand and arm horizontally and beyond the left side of the vehicle; or
(b) to the right, by extending the hand and arm upward and beyond the left side of the vehicle.
(6) A mechanical or electrical signal device shall clearly indicate the intention to turn, shall be visible and understandable during day-time and night-time from the front and from the rear of the vehicle for a distance of 30 metres, and shall be self-illuminated when used at any time from one-half hour after sunset to one-half hour before sunrise.
(7) No person while operating or in control of a vehicle upon a highway shall actuate the mechanical or electrical device referred to in subsection (6) for any purpose other than to indicate a movement referred to in subsection (1) or (2).
(8) The driver or operator of a vehicle upon a highway before stopping or suddenly decreasing the speed of the vehicle, if the operation of any other vehicle may be affected by such stopping or decreasing of speed, shall give a signal plainly visible to the driver or operator of the other vehicle of the intention to stop or decrease speed,
(a) by means of the hand and arm extended downward beyond the left side of the vehicle; or
(b) by means of a stop lamp or lamps on the rear of the vehicle which shall emit a red or amber light and which shall be actuated upon application of the service or foot brake and which may or may not be incorporated with one or more rear lamps.
“vehicle” includes a street car equipped with turn signals or brake lights, as the case may be.
Accordingly, the law requires that the signal be used to indicate an intention rather than an action. On another note, where the law states that a signal is required to provide indication of intentions where the intention may affect safe "operation of any other vehicle", a failure to signal charge appears to require proof that another vehicle was present and may be affected; accordingly, where another vehicle must be present and thus if another vehicle is absent the mandate to signal is absent. Surprisingly, the mandate to signal intention applies only to, "any other vehicle"; and apparently, without similar mandate to signal intention to pedestrians. It is also necessary to bear in mind that the law requiring signaling where the "operation of any other vehicle may be affected", fails to require the prosecution to prove that another vehicle actually was affected as the condition in law is that the "other vehicle may be" rather than was affected. This nuance was stated within the case of York (Regional Municipality) v. Switzer, 2017 ONCJ 86 where it was said:
 Section 142(1) requires that a driver signal a lane change if “any other vehicle may be affected by the movement”. In R v Clarke 2005 CanLII 15452 (ON CA),  OJ No 1825 the Ontario Court of Appeal held at paragraph 23, “To make out the offence, it is only necessary to show that another vehicle may be affected and proof that another vehicle is actually affected is not required.” The Clarke decision was recently applied in this jurisdiction on the same point – Regional Municipality of York v Conforti  OJ No 6863 (CJ). The Clarke interpretation follows the wording of the section and accords with a purposive reading of the Act which seeks to instruct drivers to make lane changes safely and does not limit the offence to those situations where collisions or near-collisions occur.
A charge of failing to signal may be successful where it is proven that a driver of an automobile failed to signal a warning of intent to change lanes or intent to make a turn if that failure could affect the operation of any other vehicle. The qualifying requirement that the failure to signal must affect another vehicle makes failing to signal and interesting charge within the Highway Traffic Act. Notably, the failing to signal charge applies only where another "vehicle" may be affected; and accordingly, failing to signal when a pedestrian may be affected is irrelevant (albeit it is still smart to signal for the benefit of a pedestrian). Also notable is the requirement that, in addition to proving that the charged person failed to signal, for a successful prosecution there must also be proven that another vehicle was in the vicinity in such a way that the operation of that other vehicle was potentially affected.