Interactive tool · October 2026
Mirrors and blind spots
A Toyota Corolla from above, drawn to scale, with what each mirror really shows and the areas no mirror covers. Drag the other cars into the gaps, or watch a car overtake you and disappear from your mirror.
Section 1
What your mirrors show
Our Corolla is in the middle lane of a three-lane motorway, driving up the page. The driver sits on the right, as in Ireland. Blue is what the interior mirror shows through the rear window, green is what the door mirrors show, and red is the blind spots: the area behind your eyes that no mirror shows. Drag the blue and the orange car along their lanes. Press Windscreen pillars to see what the pillars either side of the windscreen hide ahead of you.
Door mirrors set to show
Toyota Corolla Hatchback, three-lane motorway
Door mirrors set to show the edge of your car.
Orange car, left-hand lane
Blue car, right-hand lane
Worked out, not drawn by eye. Each mirror area comes from the law of reflection, ray by ray, from the driver’s eyes to the glass and back, stopped by the car’s own body and, for the interior mirror, by the edges of the rear window. Our measurements and assumptions: the Corolla is 4.37 m long and 1.79 m wide (2.08 m with mirrors); the driver’s eyes are about 2.28 m behind the front bumper and 37 cm right of the centre; each door mirror glass is 17 cm wide and evenly curved with a 1.2 m radius (the tightest curve UN Regulation 46 allows for an evenly curved door mirror; a flatter glass shows less, and a glass with a more sharply curved outer part, marked by a line on the glass, shows more); the interior mirror is flat and 25 cm wide; the rear window is about 1.16 m wide. Everything is drawn at window height, from above. What it cannot show: things low down close behind the car, which hide below the rear window (RotR p. 222: you cannot see a small child behind your vehicle through your mirrors or back window), and the mirror housings, which also hide part of the view ahead. Anything behind the line level with your eyes needs a mirror or a look over your shoulder. Windscreen pillars: drawn where they sit in the Corolla at eye height, taken from the same top view, and 12 cm wide across your line of sight (our assumption). The light shadow is what one eye cannot see past the pillar; the dark shadow is what neither eye can see, with your head facing forward. UN Regulation 125 allows each pillar to hide at most 6°, measured with both eyes and the head turned towards the pillar; in our drawing the right pillar hides about 4.5° and the left one about 3.8°, which at 20 m is about 1.5 m: enough for a cyclist or a pedestrian.
Section 2
A motorbike behind the pillar
Our Corolla comes up to a Yield junction at 35 km/h, ready to turn right, and brakes for the line. A motorbike is coming from the left at about 50 km/h. At these speeds the two are heading for the same spot, so from the driver’s seat the motorbike stays in the same direction all the way in, and that direction is behind the left windscreen pillar. Press play, then try again with your head further forward.
Your head
Yield junction, motorbike from the left
Worked out, not drawn by eye. The motorbike’s speed is chosen so that it stays in one direction from the driver’s eyes, the direction of the left pillar; the drawing then checks, frame by frame, which parts of it each eye can see past the pillar. The pillar is the same as in Section 1: 12 cm wide across the line of sight (our assumption). Our numbers, as an example: 35 km/h on the approach, braking at 2.5 m/s² from about 19 m before the line, positioned about 30 cm left of the centre line to turn right; a motorbike 2.1 m long. A real junction, car and rider will differ, but the effect does not depend on the exact numbers: any road user heading for the same spot as you at a steady speed stays in one direction from your seat, and if that is behind a pillar, it stays there.
Section 3
Door mirrors make cars look further away
A curved door mirror shows more of the road, but it shows everything smaller. A car in it looks as small as it would look much further back in a flat mirror. The interior mirror in our drawing is flat, so it shows a car at its true size. Move the slider to put a car behind you.
Worked out from the mirror geometry in Section 1. A curved mirror makes a smaller image of the car, closer behind the glass. Measured from the mirror, a car at distance D looks as small as it would at D × (1 + 2 × eyes-to-mirror ÷ radius) in a flat mirror. With the glass curved to a 1.2 m radius (the tightest UN Regulation 46 allows for an evenly curved door mirror), 86 cm from your eyes on the right and 1.47 m on the left, that is about 2.4 times on the right and 3.4 times on the left; the left mirror is further from your eyes, so the effect is bigger. A flatter glass makes the difference smaller; the outer, more curved part of an aspherical mirror makes it bigger. The faded car shows where the car would be if it were as far away as it looks; the real car is where it is. These numbers are about size only: drivers also use other clues, and in field tests their mistake was smaller than the size alone predicts. Every car is different: some door mirrors are flat, curved ones differ in radius, and how far the mirror is from your eyes depends on the car and on how you sit.
Section 4
Where this comes from
What the Rules of the Road say, what the mirror standard requires, and what is our own teaching.
- RotR p. 277 (glossary): a blind spot is an area a driver cannot see directly or with their mirrors; they have to turn or look sideways to see other road users there.
- RotR p. 44: your vehicle must have mirrors so that you always know what is behind and to each side; keep them clean, in good condition and correctly positioned. Use them before signalling, moving off, changing lanes, overtaking, slowing down, stopping, turning or opening doors.
- RotR pp. 51–52: before moving off, check the blind spot over your right shoulder if moving off to the right, or over your left shoulder if moving to the left. There are blind spots, so always check over your shoulders as well as in the mirrors.
- RotR p. 55: to check your blind spot when travelling at speed, take a quick sideways glance to check the position of a vehicle that may have disappeared from your view in the mirror.
- RotR pp. 56, 152–153: before overtaking, check your mirror and your blind spots. On a motorway, avoid staying in other drivers’ blind spots, and check your mirrors at least twice before changing lane: it helps you judge how fast traffic behind is approaching and see vehicles travelling in your blind spots.
- RotR p. 128: watch for mopeds and motorcycles emerging from junctions; bicycles, e-scooters, mopeds and motorcycles might be difficult to see because of their small size. p. 126: at a Yield sign or line, slow down and stop if you need to let traffic pass. p. 129: turning right from a minor road, take up a position just left of the middle of the road. p. 74: the Yield line and the Yield triangle on the road.
- Distance in curved mirrors: M. J. Flannagan, M. Sivak et al., Distance perception in driver-side and passenger-side convex rearview mirrors: objects in mirror are more complicated than they appear, University of Michigan Transportation Research Institute, report UMTRI-97-32 (1997), for the US National Highway Traffic Safety Administration. Convex mirrors made drivers overestimate the distance to cars behind; the longer the distance from the eyes to the mirror, the bigger the overestimate; in both mirror positions it was smaller than the size model predicts.
- RotR p. 222: you cannot see a small child behind your vehicle through your mirrors or back window. If in doubt, get out and check.
- UN Regulation No. 46 (devices for indirect vision; EU Official Journal L 237, 8 August 2014). A car needs an interior mirror and a main door mirror on each side (para. 15.2.1.1.1). The interior mirror must show at least a 20 m wide stretch of flat road, centred on the car, from 60 m behind the driver’s eyes to the horizon (15.2.4.1). Each door mirror must show at least a 4 m wide stretch beside the car from 20 m behind the driver’s eyes, plus a 1 m wide strip next to the car from 4 m behind the eyes (15.2.4.3). An evenly curved (spherical) door mirror’s radius must be at least 1,200 mm (6.1.2.2.4); a door mirror may also have an extra, more sharply curved (aspherical) part, and the line where it starts must be marked on the glass (2.1.1.10, 6.1.2.2.1, 6.1.2.2.3). The driver’s eyes are taken as two points 65 mm apart, 635 mm above the seat’s reference point (12.1). Press Legal minimum above to see these areas.
- UN Regulation No. 125 (forward field of vision; EU Official Journal, 31 July 2010, CELEX 42010X0731(03)). The angle each windscreen (‘A’) pillar hides must not be more than 6° (para. 5.1.2), measured with two eye points 65 mm apart, the head turned towards the pillar (5.1.2.1, 5.5). A car may not have more than two A pillars (5.1.2.2). Apart from the A pillars, side window division bars, outside radio aerials, rear-view mirrors and windscreen wipers, nothing should block the driver’s 180° forward view within the band the regulation sets out (5.1.3). The Rules of the Road do not mention the pillars.
- Our own teaching and our own measurements, not RSA figures: the three mirror settings (the Rules of the Road say only that mirrors must be correctly positioned); where the driver’s eyes, the mirrors and the windscreen pillars are, taken from a scaled top view of the Corolla; the size and curve of the mirror glass; how wide the pillars are; moving your head to look around a pillar; the motorway drawing; in Section 2, the speeds, the braking, the 30 cm from the centre line and the junction drawing (laid out as in our T-junction simulator); in Section 3, how much smaller a car looks, worked out from the mirror geometry above with the mirror equation from physics.
UN Regulation No. 46, uniform provisions concerning the approval of devices for indirect vision, OJ L 237, 8.8.2014, paras 2.1.1.10, 6.1.2.2.1–6.1.2.2.4, 12.1, 15.2.1.1.1 and 15.2.4.
M. J. Flannagan, M. Sivak, J. Schumann, S. Kojima, E. C. Traube, UMTRI-97-32 (1997), convex rearview mirrors and distance perception.
UN Regulation No. 125, uniform provisions concerning the approval of motor vehicles with regard to the forward field of vision of the motor vehicle driver, CELEX 42010X0731(03), paras 5.1.2, 5.1.3 and 5.5.
The mirror geometry is Smart Driving Academy's own calculation from the car's size; real mirrors and seating positions differ from car to car. Educational tool only. It does not replace the Rules of the Road or qualified instruction.
See also: Passing a parked car · MSMPSL at a T-junction · MSMPSL at a roundabout